Truck starts then shuts off immediately

Tiny
JOHN THEDE JR.
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 226,833 MILES
So my SUV starts and shuts down after about two seconds. First I thought it was a security issue but after replacing the ignition lock cylinder and the module it still has same issue. But now I noticed there is no security light at all illuminated. And so I hooked my scan tool to take a reading and it says trouble connecting to the computer. Any ideas?
Sunday, July 5th, 2020 AT 5:34 PM

7 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
The scan tool not connecting could be a scan tool issue or a power or ground issue with the DLC. It could also be a problem with the VCM which could be the cause of the start then stall.

I attached the wiring diagram to start testing the DLC for power and ground. You should have power on pin 16 at all times and then ground on 4 and 5. Let's check those and then hook the scan tool to another vehicle and make sure it can connect to another vehicle.

Once we know the results of this we can move onto the next step because depending on the results this may not be related to the stalling issue.

Thanks
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Sunday, July 5th, 2020 AT 7:33 PM
Tiny
JOHN THEDE JR.
  • MEMBER
  • 4 POSTS
Okay, so I have constant power to 16 and grounds 4 and 5 are good and scan tool works on other vehicle.
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Sunday, July 5th, 2020 AT 11:00 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. That means it is either a wiring issue on the class 2 bus system (purple wire) or the VCM has failed.

Test continuity from the DLC to the VCM on that purple wire. Just make sure the wiring is intact from end to end.
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Monday, July 6th, 2020 AT 7:23 PM
Tiny
JOHN THEDE JR.
  • MEMBER
  • 4 POSTS
Okay, my scan tool does connect now but my truck still starts then shuts down immediately. I'm not seeing any theft protection alerts and no security light on, but still shuts down like security would do. Also show no fault codes.
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Monday, July 6th, 2020 AT 10:26 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
That means the most common cause is the idle air control valve. I attached the info on this. I would replace this and then retest. Let us know what you find. Thanks
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Tuesday, July 7th, 2020 AT 7:43 PM
Tiny
JOHN THEDE JR.
  • MEMBER
  • 4 POSTS
Okay, here's an update for you Kenny: so I have pulled the instrument cluster and found out that the light bulb was burned out for the security light, so it is showing a security light. I have replaced the ignition lock cylinder with a brand new one and the security module from under the dash with a used one in fear that the first one might be bad because that'd been taken apart before. Testing my fuel pressure and it tested perfectly. So my pump is good, my regulators good, and all that checks out fine. So here's what I have is in fact a security issue. Where do I go from here?
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Wednesday, July 8th, 2020 AT 1:55 PM
Tiny
4DRTOM
  • MECHANIC
  • 467 POSTS
Hi John,
Are there any codes when you scan the car. There is a TSB for this issue I have attached it for you to review. Hopefully it will help.
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Thursday, July 9th, 2020 AT 2:21 PM

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