Expert: Roland Finston - 9/13/2011

Question
QUESTION: This is a follow-up to my previous question. http://www.allexperts.com/user.cgi?m=6&catID=807&expID=63082&qID=4988937

I finally traced the wiring harness from TCM to all connected end points and found no problems. I got the car started today and was able to use my scan tool on it. The codes were P0700 and P1768. Also, when the gearshift is in 3 or L all of the PRND3L lights are lit otherwise it works normally.

In addition I have a new problem in that when the car is idling the speedometer fluctuates like a tach. I had a similar problem in the past and I fixed it by removing the speedometer and cleaning the contacts.

ANSWER: Hi Bob,
I am thinking that the trans control relay contacts are either stuck closed or stuck open (there is conflicting information in my manuals as to which for this code #). It implies the problem has to do with the etax relay or its control circuit. Have you noticed either situation, above, to be the actual situation?
All the light being on at the display sometimes suggest the pci bus connection from the tcm pin 43 to pin 7 of the body control module white plug is not present.
Roland



---------- FOLLOW-UP ----------

QUESTION: Hi Roland,
The ETAX relay is working properly. I tested the relay and also swapped it out with a known good relay. A DVM confirmed that the control circuit is not energizing the relay.

I will check BCM pin 7 to TCM pin 43 and report back.
Bob

Answer
Hi Bob,
Another possibility is that the range sensor contacts are not working properly in 3 and L. Check that in 3 pin 8 (violet) is grounded, while in L 7,8,9 (light green/black, violet, violet/white) are grounded. That is how I 'read' the wiring diagrams. If there were a problem with 8 for example then the tcm would not know what to make of that which can cause all the the lights to illuminate.
Roland