solenoid short/PCM may cause shift problems

[AHar_94XLT]

I ran accross an interesting A4LD article out on the web. Evidently if the solenoid or solenoid connector shorts it will take out 3 transistors in the PCM computer. This will cause no shift (hot and cold alike). This guy changed the PCM without checking the solenoid and blew the new PCM as well - he figured it had to be the tranny, dropped and rebuilt his tranny and still had the problem. A simple check of the connector and solenoid with an ohm meter would have saved alot of cuss words.

I hope this helps someone out there....

 

[Glacier991]

Wow interesting find, can you post a link? Thank you very much for sharing that info !

 

[BrooklynBay]

The output of the PCM is a ground signal. If the solenoid's harness were shorted to 12 volts positive, then it should have blown a fuse. The transistors are similar to diodes that only let voltage travel in one direction, but are sensitive to voltage spikes. There is a clamping diode located within the A4LD's harness, but if there is a short, it will still damage the PCM's transistors. It looks like it would be a good idea to check the internal harness whenever there is a solenoid, or PCM failure. PCM's usually come with a paper explaining to check the reason for the previous failure (solenoids, shorts, etc.) before connecting a new one.

 

[BrooklynBay]

By the way, there are 2 solenoids in the A4LD, so wouldn't there only be 2 transistors involved?

 

[BrooklynBay]

Here's an artice which discusses reasons why a PCM could fail: http://www.aa1car.com/library/pcm.htm