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Discussion Starter #1
Last night the wife called with car trouble. She went in a store and everything was fine. Came back out and started the car and the CEL was on, the TC light was on, and the the display kept flashing something about the power steering. She tried to move it and the car "bug jumped" as it was moving. I drove in to get her and started the car to see what it was doing. The CEL light was on but nothing else. I decided to drive it home. Everything was good for about 5 miles and then the dash lit up like a Christmas tree. All of the above plus ABS and Security lights. One red light was on and off but it was so quick I couldn't tell what it was. Still drove fine though. Then the Speedometer started jumping all over, but the tach was fine. Still drove fine. When I was almost home and had to speed up and slow down a lot, I noticed some weird shifting. Any ideas where to start?
 

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First thing to check is the ECM/TCM fuse in the BCM fuse block for corrosion or pitting.



If everything is okay there and problem persist then check the ground under the driver's seat. You will have to remove the seat and look under carpet for this one. Because water from melting snow tends to creep to this ground and corrode it.

 

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#7 in the picture.
 

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Discussion Starter #5
The fuse looks perfectly fine. I will have to wait till the weekend to look at the ground connection. I pulled the codes from it and got 6.
U0073
P0700
U0101
P0742
P0135 pd
P0700 pd
 

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U codes mean a lost of high speed GMLan. Your P codes are probably bogus because you lost GMlan communication and will probably go away after. If it's not your ground wire under the seat you will find a broken wire somewhere.

DTC U0073
Circuit Description
The GMLAN serial data circuits are controller area network (CAN) high and/or low speed serial data buses used to communicate information between the control modules. Typical data transmission speeds must be high enough to ensure that a required real-time response is maintained. There are two different types of GMLAN serial data circuits, the High speed 2-wire circuit and Low speed single wire circuit. Refer to Data Link References for the complete description of the buses used on this vehicle. The GMLAN serial data circuits also communicate directly to the data link connector (DLC). Messages are interpreted by the externally connected CANdi module which acts as a transceiver for the scan tool.

Modules connected to the GMLAN serial data circuits monitor communications during normal vehicle operation, where operation information is exchanged among the modules. All the modules on the GMLAN networks, maintain a transmit error counter (TEC) and a receive error counter (REC). The counter values increase with detected errors and will decrease with error-free messages. If the TEC value exceeds 255, the controller removes itself from the network and DTC U0073 will result.

U0101 Lost Communication with Transmission Control Module (TCM)

Ica list your P codes if you want but don't think they're important at this time....
 

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Discussion Starter #7
The ground wire and connections under the seat look brand new. No water or snow seepage and corrosion here. I agree on the codes. Is there any way this can be related to the ignition switch recall?
 

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Doubt. I did a 2005 GMC Sierra yesterday that had similar problems turns out it was the radio gmlan pulling down the whole line. I disconnected the radio and everything worked fine. He picked up a radio from the scrapyard and had it unlocked by GM and he's good to go.
 

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Discussion Starter #9
I've been reading lots of forums on this problem. A lot of people throwing time, money, and parts at this same problem since 2007. Everyone posts "fixed" and then comes back and says its back and worse. Why is the radio on the same lan as critical system components?
 

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Low speed GMLan communicates with all CPUs in the car, ECM, TCM, EBCM, BCM,TDM, IP and radio for the chimes. It is usually a dark green wire. For instance "P1" of BCM pin #18 and #36



---------- Post added at 08:21 PM ---------- Previous post was at 08:17 PM ----------

Have you tried pulling the connectors off of your BCM and reconnecting. Sometimes corrosion causes bad contacts, do this a few times to clean them out. Disconnect battery first for safe guard.
 

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Discussion Starter #11
No I have not. Where is the BCM located? It sounds like it could be any dark green wire, connector with that wire, or a malfunctioning module connected by that wire.
 

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Well it's the BCM that has the Low speed GMLan translator, so I would start there.



 

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Discussion Starter #13
Thanks! I thought that was just a fuse box. ;) Is the whole thing the BCM or just one of the connectors?
 

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The 2 blue connectors just come out by pulling the levers (yellow arrow), the pink one has a 7mm nut, I believe.

 

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Discussion Starter #15
I tried the connections above. No change. I then tried this ( http://www.cobalt ss.net/forums/problems-service-maintenance-69/gauge-cluster-power-steering-267588/index2.html ) and the vehicle wouldn't even start. The gauges went crazy when the key was just turned to the on position and lots of clicking sounds from relays. I moved the ground wire back to its original location and sanded all the connections to make sure they were ok. I also found a ground wire to a rusty looking nut on the transmission. I cleaned it and reinstalled it. Then I started the car and no lights were on. Not even the check engine light was on. I took it for a drive and no problems. Monday it drove to town just fine. That afternoon it was right back like it started with lights, messages, and needles all over the place. Looks like I am back to the drawing board.
 
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