Help Request: P0134 P0154 Fresh Rebuild
July 3rd, 2020, 12:43 PM
#1
Help Request: P0134 P0154 Fresh Rebuild
Ok, so looking for some help on debugging and debugging procedure..keeping in mind..Im not much of a car guy...
History: Acquired vehicle approx Oct 2018, had some rough running at idle, but no codes, no overheating..but coolant seemed to be slowly losing (internally), suspected head gasket, ending up adding Bars HG1 along with other tune-up items: cap, plugs,wires, rotor, fuel filter. Did compression (found low cyl 5), But otherwise working, and yes, the Bars HG1 did seem to help significantly....fast forward to Jan 2020.
Jan 2020, CEL and Flashing CEL, limped it back home about 5 miles....P0300.. no overheating, no external leaks..another round of Bars HG1, .replaced plugs and O2 Sensors front and back...no help.....time for teardown. turns out bad head gasket as well as both heads have crack...time for a rebuild.. replaced heads, full machining, valve job, rebuild kit install.
Jun 2020: Finally get the rebuild done..[resolve a P0300 a few days ago (see my other post- had two plug wires swapped) and now that that is resolved] engine seems to be running smoothly with probably 10 miles on the fresh rebuild now but P0134 and P0154 pops up (takes a while for this code to show) Ok...so I break out the Foxwell N510 Elite for GM..scan tool and do some testing:
I seem to be in open loop all the time according to the scan tool, ( but I do get up to 93C, typically fluctuating from about 90-95C, via scan tool.). For both cold and hot engine..I get the following readings
b) STFT B1/B2, LTFT B1/B2, STFTB1S1, STFTB2S1 all at 0
c) STFT B1S1 and STFT B2S2 both at 99.2%
d) Oxy Sens Output Voltage B1S1, B1S2, B2S1, B2S2 all at 0.445 V
Q1) Can someone tell me the conceptual difference between STFT B1 and STFT B1S1?
Q2) Can someone give me some guidance on how to proceed to fix this issue along with some supporting explanation to the above readings?
History: Acquired vehicle approx Oct 2018, had some rough running at idle, but no codes, no overheating..but coolant seemed to be slowly losing (internally), suspected head gasket, ending up adding Bars HG1 along with other tune-up items: cap, plugs,wires, rotor, fuel filter. Did compression (found low cyl 5), But otherwise working, and yes, the Bars HG1 did seem to help significantly....fast forward to Jan 2020.
Jan 2020, CEL and Flashing CEL, limped it back home about 5 miles....P0300.. no overheating, no external leaks..another round of Bars HG1, .replaced plugs and O2 Sensors front and back...no help.....time for teardown. turns out bad head gasket as well as both heads have crack...time for a rebuild.. replaced heads, full machining, valve job, rebuild kit install.
Jun 2020: Finally get the rebuild done..[resolve a P0300 a few days ago (see my other post- had two plug wires swapped) and now that that is resolved] engine seems to be running smoothly with probably 10 miles on the fresh rebuild now but P0134 and P0154 pops up (takes a while for this code to show) Ok...so I break out the Foxwell N510 Elite for GM..scan tool and do some testing:
I seem to be in open loop all the time according to the scan tool, ( but I do get up to 93C, typically fluctuating from about 90-95C, via scan tool.). For both cold and hot engine..I get the following readings
b) STFT B1/B2, LTFT B1/B2, STFTB1S1, STFTB2S1 all at 0
c) STFT B1S1 and STFT B2S2 both at 99.2%
d) Oxy Sens Output Voltage B1S1, B1S2, B2S1, B2S2 all at 0.445 V
Q1) Can someone tell me the conceptual difference between STFT B1 and STFT B1S1?
Q2) Can someone give me some guidance on how to proceed to fix this issue along with some supporting explanation to the above readings?
Last edited by oldandintheway; July 3rd, 2020 at 10:07 PM.
July 4th, 2020, 12:48 AM
#2
CF Monarch
Ok, so looking for some help on debugging and debugging procedure..keeping in mind..Im not much of a car guy...
Jun 2020: Finally get the rebuild done..[resolve a P0300 a few days ago (see my other post- had two plug wires swapped) and now that that is resolved] engine seems to be running smoothly with probably 10 miles on the fresh rebuild now but P0134 and P0154 pops up (takes a while for this code to show) Ok...so I break out the Foxwell N510 Elite for GM..scan tool and do some testing:
I seem to be in open loop all the time according to the scan tool, ( but I do get up to 93C, typically fluctuating from about 90-95C, via scan tool.). For both cold and hot engine..I get the following readings
b) STFT B1/B2, LTFT B1/B2, STFTB1S1, STFTB2S1 all at 0
c) STFT B1S1 and STFT B2S2 both at 99.2%
d) Oxy Sens Output Voltage B1S1, B1S2, B2S1, B2S2 all at 0.445 V
Q1) Can someone tell me the conceptual difference between STFT B1 and STFT B1S1?
Jun 2020: Finally get the rebuild done..[resolve a P0300 a few days ago (see my other post- had two plug wires swapped) and now that that is resolved] engine seems to be running smoothly with probably 10 miles on the fresh rebuild now but P0134 and P0154 pops up (takes a while for this code to show) Ok...so I break out the Foxwell N510 Elite for GM..scan tool and do some testing:
I seem to be in open loop all the time according to the scan tool, ( but I do get up to 93C, typically fluctuating from about 90-95C, via scan tool.). For both cold and hot engine..I get the following readings
b) STFT B1/B2, LTFT B1/B2, STFTB1S1, STFTB2S1 all at 0
c) STFT B1S1 and STFT B2S2 both at 99.2%
d) Oxy Sens Output Voltage B1S1, B1S2, B2S1, B2S2 all at 0.445 V
Q1) Can someone tell me the conceptual difference between STFT B1 and STFT B1S1?
July 4th, 2020, 4:32 AM
#3
Ok, well, my current focus is to figure out why I am in open loop 'all the time', as it appears that is what the scanner is telling me directly (scanner indicates open loop explicitly), as well as indirectly (all the sensor readings being both fixed/constant and at 0). From my reading, I am under the following impressions
a) once the P0134 or P0154 code is set, you basically have to clear the code and cycle the engine in order to have another shot at seeing if close loop is established. So I will test this aspect after engine is warmed.
b) I was going to check the fuse (which is used for both sensors), but it seems this fuse also controls power to other components, so it would seem it shouldn't be the issue.
c) I have 'some' trouble believing both sensors crapped out, but I suppose this is conceivable from their exposure before the rebuild. But this seems unlikely since they were new as part of the pre-rebuild debug. I could check voltage supply across the heater element (12 v), resistance across the heater element ( approx 3-13 ohm), and voltage supply to the sensor side (0.445 apparently) easily enough.
d) My understanding is closed loop is achieved as a result of the 1) engine runner time out (function of T), 2) coolant temp above 140 F, 3) O2 Sensor actually switching, and 4) O2 sensor above 600 F (this is more of an indirect requirement in order to get the sensor to switch, but would seem to require the heater side to be functional.
e) I can only deduce that the ECT is functioning properly as its making it up to temp and holding. This seems to mean that both the thermostat is functioning as well as the temp sensor and at the right temp (195F).
f) so either the heater sensor simply isnt active/functional, or the sensor side isnt working, but the end result is that the ECM basically times out and throws the codes and puts itself back into open loop, and once it does that, it basically needs to be reset via the code clearing and engine off/on cycling.
g) Im also wondering if its some sort of ECM relearn issue, and that I could/should take the battery out of the loop, short the pos/neg lines to drain off circuit charge to the ECM and basically start anew at some point, especially if I get the codes cleared, sensors functioning and closed loop ability.
Any errors in my logic here?
a) once the P0134 or P0154 code is set, you basically have to clear the code and cycle the engine in order to have another shot at seeing if close loop is established. So I will test this aspect after engine is warmed.
b) I was going to check the fuse (which is used for both sensors), but it seems this fuse also controls power to other components, so it would seem it shouldn't be the issue.
c) I have 'some' trouble believing both sensors crapped out, but I suppose this is conceivable from their exposure before the rebuild. But this seems unlikely since they were new as part of the pre-rebuild debug. I could check voltage supply across the heater element (12 v), resistance across the heater element ( approx 3-13 ohm), and voltage supply to the sensor side (0.445 apparently) easily enough.
d) My understanding is closed loop is achieved as a result of the 1) engine runner time out (function of T), 2) coolant temp above 140 F, 3) O2 Sensor actually switching, and 4) O2 sensor above 600 F (this is more of an indirect requirement in order to get the sensor to switch, but would seem to require the heater side to be functional.
e) I can only deduce that the ECT is functioning properly as its making it up to temp and holding. This seems to mean that both the thermostat is functioning as well as the temp sensor and at the right temp (195F).
f) so either the heater sensor simply isnt active/functional, or the sensor side isnt working, but the end result is that the ECM basically times out and throws the codes and puts itself back into open loop, and once it does that, it basically needs to be reset via the code clearing and engine off/on cycling.
g) Im also wondering if its some sort of ECM relearn issue, and that I could/should take the battery out of the loop, short the pos/neg lines to drain off circuit charge to the ECM and basically start anew at some point, especially if I get the codes cleared, sensors functioning and closed loop ability.
Any errors in my logic here?
Last edited by oldandintheway; July 4th, 2020 at 4:38 AM.
July 4th, 2020, 5:14 AM
#4
CF Monarch
Ok, well, my current focus is to figure out why I am in open loop 'all the time', as it appears that is what the scanner is telling me directly (scanner indicates open loop explicitly), as well as indirectly (all the sensor readings being both fixed/constant and at 0). From my reading, I am under the following impressions
a) once the P0134 or P0154 code is set, you basically have to clear the code and cycle the engine in order to have another shot at seeing if close loop is established. So I will test this aspect after engine is warmed.
b) I was going to check the fuse (which is used for both sensors), but it seems this fuse also controls power to other components, so it would seem it shouldn't be the issue.
c) I have 'some' trouble believing both sensors crapped out, but I suppose this is conceivable from their exposure before the rebuild. But this seems unlikely since they were new as part of the pre-rebuild debug. I could check voltage supply across the heater element (12 v), resistance across the heater element ( approx 3-13 ohm), and voltage supply to the sensor side (0.445 apparently) easily enough.
d) My understanding is closed loop is achieved as a result of the 1) engine runner time out (function of T), 2) coolant temp above 140 F, 3) O2 Sensor actually switching, and 4) O2 sensor above 600 F (this is more of an indirect requirement in order to get the sensor to switch, but would seem to require the heater side to be functional.
e) I can only deduce that the ECT is functioning properly as its making it up to temp and holding. This seems to mean that both the thermostat is functioning as well as the temp sensor and at the right temp (195F).
f) so either the heater sensor simply isnt active/functional, or the sensor side isnt working, but the end result is that the ECM basically times out and throws the codes and puts itself back into open loop, and once it does that, it basically needs to be reset via the code clearing and engine off/on cycling.
g) Im also wondering if its some sort of ECM relearn issue, and that I could/should take the battery out of the loop, short the pos/neg lines to drain off circuit charge to the ECM and basically start anew at some point, especially if I get the codes cleared, sensors functioning and closed loop ability.
Any errors in my logic here?
a) once the P0134 or P0154 code is set, you basically have to clear the code and cycle the engine in order to have another shot at seeing if close loop is established. So I will test this aspect after engine is warmed.
b) I was going to check the fuse (which is used for both sensors), but it seems this fuse also controls power to other components, so it would seem it shouldn't be the issue.
c) I have 'some' trouble believing both sensors crapped out, but I suppose this is conceivable from their exposure before the rebuild. But this seems unlikely since they were new as part of the pre-rebuild debug. I could check voltage supply across the heater element (12 v), resistance across the heater element ( approx 3-13 ohm), and voltage supply to the sensor side (0.445 apparently) easily enough.
d) My understanding is closed loop is achieved as a result of the 1) engine runner time out (function of T), 2) coolant temp above 140 F, 3) O2 Sensor actually switching, and 4) O2 sensor above 600 F (this is more of an indirect requirement in order to get the sensor to switch, but would seem to require the heater side to be functional.
e) I can only deduce that the ECT is functioning properly as its making it up to temp and holding. This seems to mean that both the thermostat is functioning as well as the temp sensor and at the right temp (195F).
f) so either the heater sensor simply isnt active/functional, or the sensor side isnt working, but the end result is that the ECM basically times out and throws the codes and puts itself back into open loop, and once it does that, it basically needs to be reset via the code clearing and engine off/on cycling.
g) Im also wondering if its some sort of ECM relearn issue, and that I could/should take the battery out of the loop, short the pos/neg lines to drain off circuit charge to the ECM and basically start anew at some point, especially if I get the codes cleared, sensors functioning and closed loop ability.
Any errors in my logic here?
When the PCM determines that the time it took for the sensor to warm up is greater than one minute, or that the voltage is inactive, (not reading outside 391-491 mV) it may view the sensors (O2) as inactive or open and sets the P0134 code, thus you can't get a closed-loop mode. You may have an issue with motor oil burning, or your system is not calibrated properly and is running too rich.
July 4th, 2020, 12:20 PM
#5
So I did a little more playing this morning...
a) checked the fuse visually only..no issue of course
b) plugged in the scanner..(codes were already erased from yesterday) but re-erased it ll none the same..and then watched live data as it heated up.. saw a few things of interest
1) always in open loop, scanner also indicates it was never in closed loop since restart
2) was not getting any reading on the MAF (0.01 g/s) .. is this because it was in open loop?? I don't recall this being 0 when I was debugging P0300 a few days ago..
3) initially HO2S b1s1 was showing 'no voltage' where as b1s2, b2s1 and b2 were all showing 447 mV but as it warmed up, eventually b1s1 came in at 447mV also..
4) Pre HO2S and Post HO2S both showed as 'Ready'
5) Rich/Lean Bank 1 and Bank 2 both showed at 'Lean'
otherwise, the data values were the same as yesterday as far as I can tell.. (there are alot of different parameters and I dont know what they all mean and/or whether they are relevant for the auto in its current open loop state.
a) checked the fuse visually only..no issue of course
b) plugged in the scanner..(codes were already erased from yesterday) but re-erased it ll none the same..and then watched live data as it heated up.. saw a few things of interest
1) always in open loop, scanner also indicates it was never in closed loop since restart
2) was not getting any reading on the MAF (0.01 g/s) .. is this because it was in open loop?? I don't recall this being 0 when I was debugging P0300 a few days ago..
3) initially HO2S b1s1 was showing 'no voltage' where as b1s2, b2s1 and b2 were all showing 447 mV but as it warmed up, eventually b1s1 came in at 447mV also..
4) Pre HO2S and Post HO2S both showed as 'Ready'
5) Rich/Lean Bank 1 and Bank 2 both showed at 'Lean'
otherwise, the data values were the same as yesterday as far as I can tell.. (there are alot of different parameters and I dont know what they all mean and/or whether they are relevant for the auto in its current open loop state.
July 5th, 2020, 9:59 PM
#6
CF Monarch
So I did a little more playing this morning...
a) checked the fuse visually only..no issue of course
b) plugged in the scanner..(codes were already erased from yesterday) but re-erased it ll none the same..and then watched live data as it heated up.. saw a few things of interest
1) always in open loop, scanner also indicates it was never in closed loop since restart
2) was not getting any reading on the MAF (0.01 g/s) .. is this because it was in open loop?? I don't recall this being 0 when I was debugging P0300 a few days ago..
3) initially HO2S b1s1 was showing 'no voltage' where as b1s2, b2s1 and b2 were all showing 447 mV but as it warmed up, eventually b1s1 came in at 447mV also..
4) Pre HO2S and Post HO2S both showed as 'Ready'
5) Rich/Lean Bank 1 and Bank 2 both showed at 'Lean'
otherwise, the data values were the same as yesterday as far as I can tell.. (there are alot of different parameters and I dont know what they all mean and/or whether they are relevant for the auto in its current open loop state.
a) checked the fuse visually only..no issue of course
b) plugged in the scanner..(codes were already erased from yesterday) but re-erased it ll none the same..and then watched live data as it heated up.. saw a few things of interest
1) always in open loop, scanner also indicates it was never in closed loop since restart
2) was not getting any reading on the MAF (0.01 g/s) .. is this because it was in open loop?? I don't recall this being 0 when I was debugging P0300 a few days ago..
3) initially HO2S b1s1 was showing 'no voltage' where as b1s2, b2s1 and b2 were all showing 447 mV but as it warmed up, eventually b1s1 came in at 447mV also..
4) Pre HO2S and Post HO2S both showed as 'Ready'
5) Rich/Lean Bank 1 and Bank 2 both showed at 'Lean'
otherwise, the data values were the same as yesterday as far as I can tell.. (there are alot of different parameters and I dont know what they all mean and/or whether they are relevant for the auto in its current open loop state.
July 7th, 2020, 1:13 PM
#7
Well, swapped out the sensors...no change... the old sensors were basically brand new....checked resistance of the heater elements for each, both old and new, came in about 10.4 ohm across the board. And the MAF was fine...I had changed the default unit settings on the scanner so it was driving the value down close to zero, but of course, that was with different units...so nothing wrong with the MAF either. Still open loop..
I also checked the power supply with and without the battery in the loop. I was getting 12.58v direct measurement and about 12.28 when in circuit, supposedly nothing on of which i know.
a) So in order to test the wiring for the heater circuit from the O2 sensor connector back to the PCM..I simply check for 12v across the connector with key on.
b) Similarly, I can check the connector ground (PCM ground for the sensor) here to chassis ground by simply resistance measurement to make sure the local ground is indeed ground (and maybe even by voltage as well, but resistance seems like better approach). This is to check if there is an internal ground issue within the PCM. (and similarly I could conceivably attach a loose O2 sensor and it should start to heat up which I could verify by thermal imaging.)
c) In order to test the wiring for the sensor side, it seems i would simply test the voltage at the connector in both directions. I assume towards the computer, I should get the 0.447 volts...and towards the sensor, something in the 0-1v range ( I assume 0 volts or it would be a permanent battery. I can also check impedance towards the sensor, which should basically be open circuit and this was already done before I installed and was infinite. I should also test the voltage from wiring to chassis here as well.
From a), b) and c) I should know if there is a wiring issue (including any short/ground within the PCM)
d) is it possible that it is not related to the sensors or the sensor wiring? and if so...what could it be?
e) Are my battery supply measurements sufficiently different and indicative of a short or parasitic drain...its hot here and when i was connecting the multimeter, the voltages were sliding up, not down.
I also checked the power supply with and without the battery in the loop. I was getting 12.58v direct measurement and about 12.28 when in circuit, supposedly nothing on of which i know.
a) So in order to test the wiring for the heater circuit from the O2 sensor connector back to the PCM..I simply check for 12v across the connector with key on.
b) Similarly, I can check the connector ground (PCM ground for the sensor) here to chassis ground by simply resistance measurement to make sure the local ground is indeed ground (and maybe even by voltage as well, but resistance seems like better approach). This is to check if there is an internal ground issue within the PCM. (and similarly I could conceivably attach a loose O2 sensor and it should start to heat up which I could verify by thermal imaging.)
c) In order to test the wiring for the sensor side, it seems i would simply test the voltage at the connector in both directions. I assume towards the computer, I should get the 0.447 volts...and towards the sensor, something in the 0-1v range ( I assume 0 volts or it would be a permanent battery. I can also check impedance towards the sensor, which should basically be open circuit and this was already done before I installed and was infinite. I should also test the voltage from wiring to chassis here as well.
From a), b) and c) I should know if there is a wiring issue (including any short/ground within the PCM)
d) is it possible that it is not related to the sensors or the sensor wiring? and if so...what could it be?
e) Are my battery supply measurements sufficiently different and indicative of a short or parasitic drain...its hot here and when i was connecting the multimeter, the voltages were sliding up, not down.
Last edited by oldandintheway; July 7th, 2020 at 5:52 PM.
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July 14th, 2020, 10:30 AM
#8
So I probed all the O2 sensors back towards the PCM with the key on and sensors disconnected... and I measured a nominal 0.37V across the sensor lines and 11.2 volts on the heater supply lines, (the slightly low supply voltage on the heater circuit may be due to a low battery, as I had drained the battery after leaving a door ajar and havent full charged it back). But basically this is telling me there is absolutely nothing wrong with the o2 sensor circuit. So I am really at a loss here now.
Just to summarize current status.. P0134 and P0154. I seem to be Open Loop all the time and have the following I/M not ready signals from the scan tool:
Catalyst Monitor,
Evap System Monitor
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor
All my sensors appear to be responding and in normal ranges, including the MAF, ECT, IAT, Baro (as these seem to be the ones that feed into the I/M readiness).
I'm also a little confused on the voltage readings. The scan tool is showing sensor voltage at 0.445 V, but my direct measurement are at 0.37. I this just resistive drop of the wiring?? Seems quite a bit...
Does any one have any suggestions?? I'm completely stuck and smog is coming up...
Just to summarize current status.. P0134 and P0154. I seem to be Open Loop all the time and have the following I/M not ready signals from the scan tool:
Catalyst Monitor,
Evap System Monitor
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor
All my sensors appear to be responding and in normal ranges, including the MAF, ECT, IAT, Baro (as these seem to be the ones that feed into the I/M readiness).
I'm also a little confused on the voltage readings. The scan tool is showing sensor voltage at 0.445 V, but my direct measurement are at 0.37. I this just resistive drop of the wiring?? Seems quite a bit...
Does any one have any suggestions?? I'm completely stuck and smog is coming up...
Last edited by oldandintheway; July 14th, 2020 at 2:53 PM.
July 19th, 2020, 5:58 PM
#9
CF Monarch
So I probed all the O2 sensors back towards the PCM with the key on and sensors disconnected... and I measured a nominal 0.37V across the sensor lines and 11.2 volts on the heater supply lines, (the slightly low supply voltage on the heater circuit may be due to a low battery, as I had drained the battery after leaving a door ajar and havent full charged it back). But basically this is telling me there is absolutely nothing wrong with the o2 sensor circuit. So I am really at a loss here now.
Just to summarize current status.. P0134 and P0154. I seem to be Open Loop all the time and have the following I/M not ready signals from the scan tool:
Catalyst Monitor,
Evap System Monitor
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor
All my sensors appear to be responding and in normal ranges, including the MAF, ECT, IAT, Baro (as these seem to be the ones that feed into the I/M readiness).
I'm also a little confused on the voltage readings. The scan tool is showing sensor voltage at 0.445 V, but my direct measurement are at 0.37. I this just resistive drop of the wiring?? Seems quite a bit...
Does any one have any suggestions?? I'm completely stuck and smog is coming up...
Just to summarize current status.. P0134 and P0154. I seem to be Open Loop all the time and have the following I/M not ready signals from the scan tool:
Catalyst Monitor,
Evap System Monitor
Oxygen Sensor Monitor
Oxygen Sensor Heater Monitor
All my sensors appear to be responding and in normal ranges, including the MAF, ECT, IAT, Baro (as these seem to be the ones that feed into the I/M readiness).
I'm also a little confused on the voltage readings. The scan tool is showing sensor voltage at 0.445 V, but my direct measurement are at 0.37. I this just resistive drop of the wiring?? Seems quite a bit...
Does any one have any suggestions?? I'm completely stuck and smog is coming up...
Last edited by oilcanhenry; July 19th, 2020 at 6:03 PM.
July 19th, 2020, 8:01 PM
#10
So I've been working on this for a few more days, even had someone else look at it..and this is where Im at:
I think its more important now to focus on the inactivity of the O2 sensors...I simply cant see why the PCM is not able to show any activity from the O2 sensors.
Its flat line 0.445 V on all the sensors, all the time, hot, cold, engine on, engine off. So this morning I did the following:
a) I disconnected the 4 sensors and then jumped the high and low for each sensors signal side down at the connector together and tied them to ground, one by one, each time checking the PCM and it did show a response (0 V)
b) I also isolated the wiring by disconnecting both sides (the sensor itself and C1-blue), so that each sensor's signal wiring should be isolated/floating. I jumped the unconnected C1 side to short the high and low of each signal and then I measured resistance across the other side and got 1-2 Ohm , showing me that there was continuity I also checked the same line to ground and it was open for each one, showing my that I had both continuity and there were no shorts. And I also checked power availability on the heater circuit and it showed 12 voolt nominal for each)
c) and I followed the procedure ( below ) up until step 8/11. At step 8, Im showing an open between the low signal and VCM ground...but to find a suitable VCM ground, I had to use the ground off of C3-white/clear. So then I got to step eleven, but it seems the only real options here are to look at the VCM grounding and the exhaust grounding. The sensor suggestions there seem to have been already checked through b) above. I dont know how to ground the exhaust. There does not appear to be any dedicated ground loop/post here. And with regard to the VCM suggestions, I did check the ground from C3 that I was using and indeed it was a good ground to chassis.
d) I was able to observe by direct probing that my sensors were active as well.
So basically, my interpretation now is that my sensors are ok (from d), the connections and the lines seem ok from (from b) and the VCM seems ok in terms of being able to force a response (from a) other than step 8..but Im sort of stuck now as I dont know what to do for step 11 (assuming I did the correct procedure in step8). If you have the same auto and are able to validate step 8, that would certainly help..or have other suggestions. (Im also wondering if there is some other aspect that may be forcing the O2 sensor response to effectively sit at 0.445V when there is nothing wrong with the O2sensor circuit - is that possible?)
https://www.gmtruckclub.com/threads/...1473186/page-3
I think its more important now to focus on the inactivity of the O2 sensors...I simply cant see why the PCM is not able to show any activity from the O2 sensors.
Its flat line 0.445 V on all the sensors, all the time, hot, cold, engine on, engine off. So this morning I did the following:
a) I disconnected the 4 sensors and then jumped the high and low for each sensors signal side down at the connector together and tied them to ground, one by one, each time checking the PCM and it did show a response (0 V)
b) I also isolated the wiring by disconnecting both sides (the sensor itself and C1-blue), so that each sensor's signal wiring should be isolated/floating. I jumped the unconnected C1 side to short the high and low of each signal and then I measured resistance across the other side and got 1-2 Ohm , showing me that there was continuity I also checked the same line to ground and it was open for each one, showing my that I had both continuity and there were no shorts. And I also checked power availability on the heater circuit and it showed 12 voolt nominal for each)
c) and I followed the procedure ( below ) up until step 8/11. At step 8, Im showing an open between the low signal and VCM ground...but to find a suitable VCM ground, I had to use the ground off of C3-white/clear. So then I got to step eleven, but it seems the only real options here are to look at the VCM grounding and the exhaust grounding. The sensor suggestions there seem to have been already checked through b) above. I dont know how to ground the exhaust. There does not appear to be any dedicated ground loop/post here. And with regard to the VCM suggestions, I did check the ground from C3 that I was using and indeed it was a good ground to chassis.
d) I was able to observe by direct probing that my sensors were active as well.
So basically, my interpretation now is that my sensors are ok (from d), the connections and the lines seem ok from (from b) and the VCM seems ok in terms of being able to force a response (from a) other than step 8..but Im sort of stuck now as I dont know what to do for step 11 (assuming I did the correct procedure in step8). If you have the same auto and are able to validate step 8, that would certainly help..or have other suggestions. (Im also wondering if there is some other aspect that may be forcing the O2 sensor response to effectively sit at 0.445V when there is nothing wrong with the O2sensor circuit - is that possible?)
https://www.gmtruckclub.com/threads/...1473186/page-3