2005 2500 Suburban No Crank
#11
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Ted K (May 27th, 2024)
#12
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so you did. I should read more carefully ![Embarrassment](https://chevroletforum.com/forum/images/smilies/redface.gif)
yeah I was saving the backprobing for last
![Embarrassment](https://chevroletforum.com/forum/images/smilies/redface.gif)
yeah I was saving the backprobing for last
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Ted K (May 27th, 2024)
#13
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The starter relay (under the hood fuse block) should have power on 2 of it's terminals. Sorry this schematic does not show the relay terminal numbers.
There are 3 fuses that are in the starter circuit. IGN E (10A), IGN A (40A), CRANK (10A).
The starter relay coil (85 or 86) gets power from the IGN E fuse via the Park/Natural Safety switch.
One of these terminals should have power all the time.
The relay is energized from the PCM (Powertrain Control Module) by grounding the circuit from the relay.
Check that the CRANK fuse gets power when the ignition switch is in the CRANK position. This fuse provides the PCM with the crank command from the ignition switch.
There are 3 fuses that are in the starter circuit. IGN E (10A), IGN A (40A), CRANK (10A).
The starter relay coil (85 or 86) gets power from the IGN E fuse via the Park/Natural Safety switch.
One of these terminals should have power all the time.
The relay is energized from the PCM (Powertrain Control Module) by grounding the circuit from the relay.
Check that the CRANK fuse gets power when the ignition switch is in the CRANK position. This fuse provides the PCM with the crank command from the ignition switch.
There is obviously something that I don't understand about the start/neutral safety switch powering the ign E switch, since there is power there even when the shifter lever is in drive and reverse. Anyway, I'm ready for that brain meltdown gentlemen!
#14
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Good. So 85 must be the positive side of the coil. It also means IGN E fuse is good, and PNP switch is good.
Now measure resistance between socket #86 and battery ground. Should drop to around zero when key is turned to crank.
If still no luck, we move on to the PCM. Connector end views should be in that same manual. Were you able to find it?
you mean the IGN E fuse? If you look near the top of the schematic it always has power when key is in run or start position.
Last edited by mountainmanjoe; May 27th, 2024 at 6:30 PM.
#15
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First of all, thank you very much for your help! 1. Terminal 85 has power all the time. 2. I don't have any power at #86 3. The crank fuse is getting power in the crank command from the ignition switch and the fuse is good.
There is obviously something that I don't understand about the start/neutral safety switch powering the ign E switch, since there is power there even when the shifter lever is in drive and reverse. Anyway, I'm ready for that brain meltdown gentlemen!
There is obviously something that I don't understand about the start/neutral safety switch powering the ign E switch, since there is power there even when the shifter lever is in drive and reverse. Anyway, I'm ready for that brain meltdown gentlemen!
![Embarrassment](https://chevroletforum.com/forum/images/smilies/redface.gif)
The relay terminal 85 should loose power when the shift lever is moved out of park or neutral.
Don't forget to put the relay back in it's socket.
Did you check the connectors at the PCM? Unplug, check for corrosion, loose pins, chewed wires, etc...
Plug them back in. Try to start one more time. Sometimes unplugging/plugging the connectors will clean the pins/sockets.
PCM Connectors
Using a paper clip from the back side of the connector will permit you to check for proper voltages.
Green connector, terminal 59, purple wire, should get power when the key is turned to START.
Blue connector, terminal 39, yellow / black wire, should have 12v with the key in RUN position. 0 volts when key is at START.
Grounding this terminal should crank the engine.
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mountainmanjoe (May 27th, 2024)
#16
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very good. Ignition switch works. Getting closer.
Good. So 85 must be the positive side of the coil. It also means IGN E fuse is good, and PNP switch is good.
The ohm meter did not even wiggle when I performed this task.
If still no luck, we move on to the PCM. Connector end views should be in that same manual.
Yes, I found it.
you mean the IGN E fuse? If you look near the top of the schematic it always has power when key is in run or start position.
Good. So 85 must be the positive side of the coil. It also means IGN E fuse is good, and PNP switch is good.
Now measure resistance between socket #86 and battery ground. Should drop to around zero when key is turned to crank.
If still no luck, we move on to the PCM. Connector end views should be in that same manual.
Were you able to find it?
you mean the IGN E fuse? If you look near the top of the schematic it always has power when key is in run or start position.
#17
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how much did it read?
perfect. Now follow Bruce's instructions for "PCM Connectors".
Hopefully it's just some corrosion on the PCM pins.
Hopefully it's just some corrosion on the PCM pins.
#18
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My mistake
My post #9 incorrectly said "all the time", the IGN E fuse will have power when the ignition switch is in the run or start position.
The relay terminal 85 should loose power when the shift lever is moved out of park or neutral.
Don't forget to put the relay back in it's socket.
Did you check the connectors at the PCM? Unplug, check for corrosion, loose pins, chewed wires, etc...
Plug them back in. Try to start one more time. Sometimes unplugging/plugging the connectors will clean the pins/sockets.
PCM Connectors
Using a paper clip from the back side of the connector will permit you to check for proper voltages.
Green connector, terminal 59, purple wire, should get power when the key is turned to START.
Blue connector, terminal 39, yellow / black wire, should have 12v with the key in RUN position. 0 volts when key is at START.
Grounding this terminal should crank the engine.
![Embarrassment](https://chevroletforum.com/forum/images/smilies/redface.gif)
The relay terminal 85 should loose power when the shift lever is moved out of park or neutral.
Don't forget to put the relay back in it's socket.
Did you check the connectors at the PCM? Unplug, check for corrosion, loose pins, chewed wires, etc...
Plug them back in. Try to start one more time. Sometimes unplugging/plugging the connectors will clean the pins/sockets.
PCM Connectors
Using a paper clip from the back side of the connector will permit you to check for proper voltages.
Green connector, terminal 59, purple wire, should get power when the key is turned to START.
Blue connector, terminal 39, yellow / black wire, should have 12v with the key in RUN position. 0 volts when key is at START.
Grounding this terminal should crank the engine.
Green connector, terminal 59, purple wire, had no voltage when turned to START.
So correct me if I need to redo the test with the connectors hooked up to the PCM. Thanks, TK.
#19
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Thanks again! I don't think the pins are corroded. The seals were good between the connectors and the PCM and everything looks good with the pins. I just responded to Bruce and I'll see what he says. TK.