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Hello majik755

Have you any update to this problem?

Anyhow, I stumbled across a description of a problem that is similar to yours in that it doesn't set a code, but otherwise it is different:

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No Crank, PRNDL Inoperative
Owners of some 2005 Chevrolet Corvettes and 2004 - 05 Cadillac XLRs may experience a no-crank condition, with no codes in any module. The concern may be followed by an inoperative transmission range indicator (PRNDL). The Tech 2 will show the transmission range circuits are all reading high when any gear is selected.

Check for a loose or broken ground G402 at the right rear suspension cradle. See SI document 1495107.

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Not sure how helpful this can be, but it does highlight a means to have a fault without a fault code.
 

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You are sure that this problem is from within the ECM or BCM ? No small 'split second event' anywhere thruout the 'can network' could effect the ECM in this way ? I'm finding it hard to understand how a BCM internal problem would not 'throw any codes' when the ECM is still operating the car/motor in normal fashion. First of all, it happens "at start up", I read nothing about any other operational activity. Second, the "Service Engine Soon" warning is directed to 'engine only questions' and not 'body' or 'accessory' related. The ECM (as I have quickly read on line) is the 'king' of this vehicle's 'domain' and has 'rule' over the BCM. (right ?) This means that IF the BCM WANTED to DO ANYTHING, the ECM would be required to allow the BCM to do that action. The ECM sends a signal to the BCM, put the "SES lamp" on. The BCM reads that signal, sends a reply 'yes I put on the "SES lamp" (in English or other) right now. The ECM would reply 'OK' handshake. "Signal sent, reply/action, handshake". IF the BCM (were malfunctioning) sent/action "SES lamp", the lamp would come on, the reply back to the ECM would be sent at the same time and the ECM would NOT OK HANDSHAKE, it would throw a code. Because the ECM didn't send any signal for any action/reply to the BCM. IMHO, the ECM can and will operate without the BCM functions operational, but the BCM cannot function without the ECM. Correct ? I offered the above insite because I know that the "GM and Mercury Marine" can systems are almost identical in structure and software. GM designed both/all of these systems. Along with the fact that I have found this problem in the Mercury Marine DTS systems. (fly by wire) It's a long story, but it did take over 75 hours of testing (3 months) of "one change/test" at a time.
I'm very happy to know that someone around here has a factory manual and is able to read it! IMHO the ECM MUST OK all messages/functions or the ECM is at fault. Also, IMHO vehicle movement and control are priority over all 'body and accessory modules'. So the ECM is the KING of the kingdom.
 

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I do not know if you ever solved the problem but I know the solution to your problem if you do still have the car or if they ever fixed it. Msg back here and I will tell you what to do.

Car is back in the shop. Still getting intermittent SVS message in the DIC, but no error codes in any of the computers, none of the history, nowhere.

After raising a stink with the Director of Service, there was miraculous contact made with GM engineers, including the guy (Chris I think?) who was responsible for the XLR line when it was in production. They are running some tests he suggested, and he is on his way to Atlanta where he says he will see and discuss the problem with one of the best XLR techs he worked with. So I am in waiting mode until tomorrow.

Here's the interesting part. He agrees with my local tech that it is a body problem being processed by the BCM or a problem with the BCM. They all agreed that the GM Service manual and other documentation is wrong. The BCM is solely responsible and sets the Service Vehicle Soon message. The ECM sets and controls the Service Engine Soon and Engine light. Who am I to argue?

I'll keep you ll posted. Oh yeah, they said if these tests or worst case replacing the BCM doesn't work, they're at a loss :skep
 

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From his post on the other forum, he recommends disconnecting the transmission solenoid to bypass the safety interlock due to the cost of the new part (~$180.)

Peace of mind . . . priceless.

CC :nono
 
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