Join Now
International Automotive Technicians Network
An Interesting Diagnosis
Posted to Technical Discussion Forum on 6/21/2011 104 Replies

This Vehicle is repaired. This is a case history only.

A 2008 Impala was dropped off today. I was given the R.O. which stated "Vehicle will not crank at times. This only occurs when the PRNDL indicator is not operating. If the PRNDL indicator is functional, the vehicle will crank and start every time. The PRNDL never stops operating when the car is running and the car never shuts off by itself."

There was no other information available as this was a used vehicle from a car lot that was dropped off. It was a V6 automatic with no added on modifications.

I went out to the drive to get the car. When I turned the key, the vehicle would not crank. The PRNDL was lit up but the gear position indicator (a circle around the letter) was not lit. I went back into the shop for the tech 2 and ran a fast module scan. There was no communication with the ECM, TCM, BCM or VCIM. Suddenly, the gear position indicator illuminated and the car started. At that point, I had normal communication with all modules.

I drove the car inside and tried starting and restarting several times with no problem. I let it sit for 15 minutes while I finished another vehicle and when I returned and turned the key to the run position, the indicator did not illuminate. Leaving the key in the on position, and doing nothing to the car, after 30 seconds the indicator illuminated by itself and the car started.

Trying it several more times, I found that if I left the key off for 10 minutes or so, when the key was turned to run, the indicator would not illuminate and the car would not crank. If the key was then left in the run position, after 20 seconds to 45 seconds, the indicator would illuminate and the car would start.

I know how I diagnosed it. How would you?

James from Florida

104 Replies Received (View Replies)