GMC Yukon won't turn over - random indicator lights

nickb2

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being nice here, plz tell us all steps you take in diagnosis of this problem, easier for us to help you. :thx a simple fix is not a oil change, check circuits given in previous post, report back findings. Check for shorts, opens and wiggle test wiring with a dvom. 8)
 

Cassabaum

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The old man said:
How long has this problem been going on? Did it just happen lately? Were you driving it daily? Did it start and run ok in the past week or so? Need to know when this issue started.

Before you start replacing or indexing a switch you need to use the schematic below and check for voltages and continuity at various points. Like check for voltage at the neutral safety switch at the transmission when the key is in the "ON' position, voltages at the starter relay, voltages at the starter coming from the battery etc. and etc.. Have you tried jumping across the starter to see if the starter will actually work?
Thanks for the schematic. We will start checking voltages tomorrow morning and I'll let you know the results.

History of problem:
- Daily driver, no problems
- Drove vehicle to child's school last week to drop off for school, approximately 10 miles round trip, vehicle sat for approximately 5 hours, then got in to start and engine would not crank (no click, nothing) - no gear position indicator, random instrument lights, rear wiper random movement

Again, thanks for your continued patience and suggestions for the next step
 

Cassabaum

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kev2 said:
1st - does this vehicle have a remote starter? that changes the circuits.
2nd- lets work the computer issue next-
you have 12v at terminal #16 and #4 is ground.... then conform YOUR code reader-
>>> suggestion take to autozone, advance, orielys parts stores for a FREE scan - might be nothing there BUT it will confirm and eliminate issues.

3rd- you can use a dvom so we can pick circuits to test for power in different key positions BUT #1 needs ans.
1st response: No, vehicle does not have a remote starter
2nd response: Verified code reader on another vehicle (very similar vehicle: 2004 GMC Denali)
3rd response: We will start checking circuits per schematic from your colleague "the old man" tomorrow

Thanks again for your patience and continued suggestions on "next" steps
 

Cassabaum

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The old man said:
How long has this problem been going on? Did it just happen lately? Were you driving it daily? Did it start and run ok in the past week or so? Need to know when this issue started.

Before you start replacing or indexing a switch you need to use the schematic below and check for voltages and continuity at various points. Like check for voltage at the neutral safety switch at the transmission when the key is in the "ON' position, voltages at the starter relay, voltages at the starter coming from the battery etc. and etc.. Have you tried jumping across the starter to see if the starter will actually work?
*** New trouble shooting information *****
We started measuring voltages using the schematic you sent us.
1) First we verified the starter operation by jumping pins 30 and 87 on the starter relay and the starter engaged.
2) Second we verified the signal from the Park/Neutral position switch on pin 85 of the Starter Relay: We had 12 volts when in Park or Neutral and 0 volts in R, D, 3, 2, and 1
3) When measuring pin 86 on the starter relay, the voltage stayed at 9 volts when the ignition switch was in the "on" position and in the "start" position. I believe the voltage should have gone to 0 volts in the start position. Is that correct?
4) Assuming pin 86 should have gone to 0 volts when the ignition switch was in the start position and did not, we then verified continuity from pin 86 on the starter relay to pin 39 on connector C1 of the PCM.
5) We also verified that pin 59 on connector C2 went to 12 volts when the ignition switch was moved to the "start" position

Given the trouble shooting steps above, it seems that the PCM is not providing 0 volts on pin 39 of C1 when the ignition switch is in the "start" position.

Do you have a schematic for the PCM so I can tell if the PCM is bad or if the PCM is not receiving the correct signals (besides pin C2-59) to create the 0 volts condition for the "start" ignition switch position.
 

The old man

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Pin 39/C1 is the ground connection for the starter relay coil. It is normally open until it gets a signal to close and go to ground. I suppose it is the "Crank Signal" when you turn the key to start. I have a schematic that shows that. Take the starter relay out and put 12v voltage to the coil, ground the other side and see if the starter relay works. With all this backfeeding of voltages, I wonder if your PCM has lost its ground. Anyway you have more testing to do. The car should turn over if you can get a ground to the starter relay. Pin39/C1 should show ground when in the start position.
 

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Cassabaum

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The old man said:
Pin 39/C1 is the ground connection for the starter relay coil. It is normally open until it gets a signal to close and go to ground. I suppose it is the "Crank Signal" when you turn the key to start. I have a schematic that shows that. Take the starter relay out and put 12v voltage to the coil, ground the other side and see if the starter relay works. With all this backfeeding of voltages, I wonder if your PCM has lost its ground. Anyway you have more testing to do. The car should turn over if you can get a ground to the starter relay. Pin39/C1 should show ground when in the start position.

fixed :) ************* PROBLEM FIXED !!!!!!!!!!!!!!! ********************** fixed :)
Thank you to everyone who helped steer us in the right direction!!! The schematics were the "road map" we needed to track down the problem!!!! Here's what we found:
1) PCM pin C1-39 was not providing 0 volts when the ignition switch was moved to the "start" position
2) When we checked the grounds on the PCM, i.e. pins C1-1,24,27,40,64,and 67 they were "floating"
3) We found a grounding diagram on-line on the AutoZone website which led us to check ground at S103 tie point, and we found that was also "floating"
4) We traced the wire from S103 to ground point G103 and we found that pack-rats had chewed through the ground wire to ground point G103!!!!
DIRTY ROTTEN PACK-RATS!!

Repaired the ground wire and now everything works great :ROFL

Thanks again to everyone that helped!! Especially "the old man" who sent us the schematic!!

How can I contribute to this forum to keep it going?
Sincere appreciation - Bill
 

The old man

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That is great. You did a great job of testing and posting the results. It makes it a lot easier for the mechanics on this site to help when the person that posted keeps them up to date as to what was done. Process of elimination. Thanks for posting the fix and how it was done. It helps everybody on this site.

If you want to contribute, go to the top of the page and click on "KEEP BAT ALIVE", and go from there.They do have great mechanics on this site.
 

nickb2

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I would love to know how you did that rolling fixed ting. Look cool. Been here a while, never have seen that. plz tell me how you did that.
 

Cassabaum

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nickb2 said:
I would love to know how you did that rolling fixed ting. Look cool. Been here a while, never have seen that. plz tell me how you did that.
for the rolling "fixed message", I selected the text and then hit the "<-M<-" Marquee button (you will see the rolling "M" on the button when you look at the text options above the box where you are entering text)
 

Cassabaum

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The old man said:
That is great. You did a great job of testing and posting the results. It makes it a lot easier for the mechanics on this site to help when the person that posted keeps them up to date as to what was done. Process of elimination. Thanks for posting the fix and how it was done. It helps everybody on this site.

If you want to contribute, go to the top of the page and click on "KEEP BAT ALIVE", and go from there.They do have great mechanics on this site.
Thanks again for your help!! I will go to the "Keep Bat Alive" and contribute! I am very glad I found this forum!
 

nickb2

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:thxu hope it works this is hilarious, for donation, click on my pay pal button, not one red cent goes in my pocket, just the site :thx
 

Idsalas

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fixed :) ************* PROBLEM FIXED !!!!!!!!!!!!!!! ********************** fixed :)
Thank you to everyone who helped steer us in the right direction!!! The schematics were the "road map" we needed to track down the problem!!!! Here's what we found:
1) PCM pin C1-39 was not providing 0 volts when the ignition switch was moved to the "start" position
2) When we checked the grounds on the PCM, i.e. pins C1-1,24,27,40,64,and 67 they were "floating"
3) We found a grounding diagram on-line on the AutoZone website which led us to check ground at S103 tie point, and we found that was also "floating"
4) We traced the wire from S103 to ground point G103 and we found that pack-rats had chewed through the ground wire to ground point G103!!!!
DIRTY ROTTEN PACK-RATS!!

Repaired the ground wire and now everything works great :ROFL

Thanks again to everyone that helped!! Especially "the old man" who sent us the schematic!!

How can I contribute to this forum to keep it going?
Sincere appreciation - Bill
I'm having trouble identifying which pin is which. Can someone help? I'm having the same issue
 

NickD

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Did you know our wonderful EPA banned electroplating, company I worked for had to ship contacts to Taiwan or Mexico to get this done, GM skips this practice, had several GM ignition switches apart, bare copper, copper oxide, darn good electrical insulators.

Before diodes, we were using copper oxide rectifiers to convert AC into DC, polished the GM contacts with power buffer and coated with, darn, can't remember, but a special anti oxidation paste and lubricant, then they would be good for several more years. Some of the contacts have several inside the switch were rated by GM up to 60 amperes.

No sense in paying a fortune for a new one that sat on a dealers shelve for 17 years, more than likely also oxidized.

You have off, accessories, run, and start in these switches.
 
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