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I034 & PCM "squirreled"

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It's been a while since I've posted here, but I'm really, really stumped on this one:

Started getting "I034" (which is "loss of PCM data") and a similar complaint from the TCS. Following troubleshooting tree in the FSM, leads me to replace PCM (car was running awful as well... no idle control, transaxle stuck in 1st (or 2nd?), shifts into gear with a "bang"). The problem is intermittent... most times, disconnecting the battery causes condition to clear... for a day or so. When PCM is in it's "hosed" mode, the IPC can't get data from PCM... resetting power of course automatically clears codes. I disconnected the ACP and ALDP (assembly line diagnostic port--under dash) to break the data bus in two places, thereby isolating the ETBCM, RSS and ACP computers from the IPC and PCM... my theory being that some other box was spewing trash on the data bus, causing the PCM to get hosed... no luck there.

Most interesting is that the PCM is still hosed when only the 2nd (white) connector is connected. Yes, I've checked power feeds and grounds, including crawling under the oily underside, and physically wiggling G102 ground on the back of the engine block to make sure it's secure. Battery terminals are clean and tight, voltages seem normal. Any one seen anything like this? Any suggestions will be welcome...

In case it doesn't show in my profile, this is on a '94 STS that I've known very well for 13 years... :) Thanks!

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I would replace the PCM with a known good PCM and see if it improves. You have done a lot of trouble shooting, my initial guess would be an intermittant connection at the battery or the underhood relay buss. I assume from your note that you checked the PCMs power source, does it originate from a relay? I have to look at my 95 manual.

Explain what you mean by "the PCM is still hosed when only the 2nd (white) connector is connected"

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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