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6 speed -no start- TCM shorted

34630 Views 5 Replies 4 Participants Last post by  DMAXchris
Be careful when jump starting another vehicle-- can fry the $1,000 TCM.
Document ID: 2074199
#PIP3605A: CTC U0101
No engine crank and no communication with TCM
Feb. 29,2008

Models affected:
2006-2007 Chevrolet Silverado Classic
2007-2008 Chevrolet Silverado
2006-2007 GMC Sierra Classic
2007-2008 GMC Sierra
Equipped with Allison LCT-1000(RPO-MW7)Automatic Transmissions
Customer may comment that the vehicle will not crank or start/will not shift after vehicle has been jump started due to battery run down or after installation of after market equipment.Technicians may find no communication with the TCM and or DTC U101 [my PPE had only a C101,which I know isn't the actual DTC]stored in other modules.
A few TCM's have been returned from the field for analysis because of the above symptoms.The field returned TCM's were analyzed and found to have two battery ground nodes inside the TCM damaged by excessive electrical current passing through the heatsink of the TCM.The nodes affected described as wire bonds are wire tied to pins 9 and 69[battery ground pins] of the TCM.
The TCM is manufactured so that the heatsink of the TCM is isolated from all vehicle electrical systems including vehicle chassis ground.Do not ground welders,battery chargers,electrostatic painters or any other equipment to the heatsink.Disconnect the 80 way connector from the TCM when electrically welding etc. to the vehicle.
To avoid damaging the TCM in this manner,NEVER ALLOW the following:
1. Battery positive wires to touch the heatsink of the TCM[e.g.When jump starting vehicle]
2. Positive battery power chassis harness wire to pin 10 and pin 70 of the TCM to be wired without fuse protection of 10-15 amps.
3. Physical contact between heatsink and vehicle chassis or other ground circuit points.
4. Electrical grounding of devices such as arc welders,battery chargers,and electrostatic painters,or jumper cables to the TCM heatsink.

Recommendations/Instructions: Take the following steps to check for damaged ground wire bondsif the symptoms for a concern are ''No Engine Crank'' and/or ''No Communications'' with Tech II.
1.Switch ignition key off.
2. Disconnect the TCM electrical connector and remove TCM from the vehicle.
3. Test for continuity between pins 9 and 69 at the TCM.If continuity exists between pins 9 and 69,then refer to steps in eSI for ''NO Engine Crank'' and/or ''No Communications''

If the circuit between pins 9 and 69 have no continuity,then the TCM has been damaged/shorted from some sort of external source shorting to the heatsink of the TCM.

1. Inspect for the source that shorted the TCM heatsink.
2. Eliminate or repair the source or condition that caused the damage.
3. Replace damaged TCM after the condition that caused the TCM damage has been corrected.

NOTE: Visual surface pits and carbon deposits are typically found on the TCM heatsink when high energy arcs are generated by shorts between the heatsink and battery power.
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Yes, several did ground the TCM and was able to get it started. They usually replace the TCM for a $$$$ after. I know I would try it.

I don't know how they did it-- maybe someone will post.
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