pctgreg

In short, too cold too long. Truck warms up to and hangs round the white mark between 160 and 210. I replaced the coolant temp sensor, and the thermostat with oem parts from the Chevy Dealer. No change in needle position. I reset the code and a week later were back again with the same code.

When i beat on the truck 2 different times last weekend after doing the thermo, I got the temp to rise up to 195ish according to my scan tool and gauge. For whatever reason it just hangs low and wont warm all the way up on its own.

Truck was in an accident over the summer, and got the front end replaced. New radiator is all I know. I'm at a loss... All threads point to thermo or temp sensor, and I went with OEM parts so I wouldn't have a problem and I still do. Could it still be the thermo? Could it be the fan clutch? Any help would be appreciated.

wgf

do you have the air temp reading from the last scan?
the way it was explained to me...your control module compares ECT to IAT during warm-up. perhaps it's that side of the logic that's causing you grief?

new radiator.
is coolant resevior filled and system completely purged?
some folks claim that an air-lock can cause either low or high coolant temps depending on the location.

I was one of the folks that survived p0128 with just a new thermostat.
but some think the real problem lies with the ECTS circuit and/or the controlling logic being too fussy.
a bad connector at either end,corroded or frayed wires are still good things to look for.

are you sure you have a 195F thermostat?
it only took a few degrees of xtra temp from my new thermostat to make the error go away.

good luck,
-bill

pctgreg

Bill,

I do not have the air temp reading from the last scan. I remember specifically looking for it twice in the scanner, and I did not see it. I know it shows on my Dodge so I know the scanner is capable of it.

The radiator was put in over the summer after an accident. I don't think it is relevant to the actual problem since this was 6 months ago, but something I just wanted to note of just in case. In my past experience, air pockets cause it to run hotter than cooler, but I guess it is possible. The resivour is filled to the proper line.

I kept the thermostat box, the numbers on it are ...

ACD# 15-11057
GM# 12600172

I didn't see the temperature stamped on the thermostat before I installed it. It could have been on the front of the t-stat, but this one came pre-installed into the water neck and did not check it visually.

Edit

Pulled the old thermostat I saved out and it says 86 celcius = 186f I looked at a few autostores, and it is showing 186 is stock.

wgf

I agree,
low water level will certainly raise the water temp.
my poor writing skills omitted that if the temperature sensor was sitting in a pocket of air it would take longer to detect the true water temps.

assuming all the parts are correct you may want independant confirmation that the coolant temp is the same value logged by your control module and gage.

the temperature sensor is only a variable resistor placed in a simple circuit to measure the voltage drop acorss the resistor.
if the resistance in other parts of the circuit changes, the "measured" voltage drop will indicate the wrong temp.

frayed wires, corrosion, bad connectors could easily do this to you.
the control circuit is probably fine, but if the normal suspects dont resolve your problem you may want to confirm keys values to the rest of the circuit.
i.e.
-the initial voltage supplied to the circuit
- the value of the fixed resistoror
-resistance of the different wires and connectors

do the dash temp gage and control module get their input from the same sensor?
does ECT reading from the scanner match the dash temp gage?
are radiator fans running when the should not?

-bill

pctgreg

Bill,

I appreciate help once again. Tonight I tried to confirm the reported temperature the best I can. The cluster gauge and my scan tool are both reporting the same values. I left the new temp sensor in the block, and pulled the old one I saved back out, and hooked it to the connector. I boiled a cup of water in a coffee mug in the microwave. I did this twice just to confirm it was close to boiling. The gauge moves to the middle white mark where it has been hanging out lately when fully warmed up. So this means that the actual coolant temp is not being reported correctly to the pcm? I still wish there was a way I could verify actual coolant temp when operating just to make sure.

Also fwiw my IAT sensor is off about... 7 degrees + or - when cold.

Does anyone have a .pdf FSM for these trucks that I can dig through the wiring diagrams for. I would assume that these wires probably go directly to the pcm, but what do I need to check for resistance wise, power wise, etc...

Thanks in advance!

wgf

sorry,
it aways sucks when the clues dont get you to the answer fast enough.

you should probably give everyone a few details to get advice more specific to your truck.
year, model, engine etc?

the specifics definitely change from year to year.
if the truck is more then a few years old, i bet a cheap Haynes manual would have the wiring diagram.
local libraries would have Chiltons.
pm an e-mail address to me and i can send anything i may have that fits.
when all else fails, there is always Google
-bill

pctgreg

Bill,

I apologize, I should have known better to provide details from the beginning.

04 silverado 4x4 5.3L Base

I tried google for the past few days and haven't turned up much. Wouldn't you know it I took another minute to search and found this.

pin 74 - signal
pin 80 - reference

It looks like the wires connect directly to the PCM according to the diagram.

Thanks again Bill!