U0101 GMC - Lost Communication With Transmission Control Module

Repair Importance Level: 3/3
Repair Difficulty Level: 3/3   
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Possible causes

  • Faulty Transmission Control Module (TCM)
  • TCM harness is open or shorted
  • TCM circuit poor electrical connection

Tech notes

Document ID: 2074199
#PIP3605A: CTC U0101
No engine crank and no communication with TCM
Feb. 29,2008

Models affected:
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 U0101 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.

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 O Engine Crankand/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.

Service Bulletin
There is a factory service bulletin for the following GMC models:
2007-2010 GMC Sierra
2007-2010 GMC Yukon Models
2008-2010 GMC Sierra Hybrid
2008-2010 GMC Yukon Hybrid
GMC Factory Service Bulletin OBDII Code U0101

There is a factory service bulletin for some models with U0101 code, the factory recommends that prior to any parts replaced there are several areas that should be inspected:
- One area is the transmission connector pins, for damaged terminals or poor terminal fit.
- Another area is the under hood fuse block for damaged terminals or poor terminal fit and mispositioned fuses in fuse block.
- Another area to inspect would be the TCM ground.
- As always powers and ground should always be load checked to make sure the circuits are able to work properly.
- Another common area would be to check the harness for rubbing through on any sharp objects mainly on top of transmission where harness can contact sharp area on engine block.

Possible symptoms

  • Engine Light ON (or Service Engine Soon Warning Light)

U0101 Gmc Description

Modules connected to the high speed General Motor Local Area Network (GMLAN) serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. The supervision time-out period is 250 ms. Each message contains the identification number of the transmitter module.
OBDII Code U0101 Gmc - Lost Communication With Transmission Control Module  - AutoCodes.com

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