Lost Communication With Transmission Control Module
Table of contents
U0101 CHEVROLET Possible Causes
- Faulty Transmission Control Module (TCM)
- TCM harness is open or shorted
- TCM circuit poor electrical connection
How do I fix code U0101 CHEVROLET?
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins.
Tech Notes
- 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
- Equipped with Allison LCT-1000(RPO-MW7)Automatic Transmissions
- Customer may comment that the vehicle will not crank or start/will not shift after the vehicle has been jump-started due to the battery run down or after installation of aftermarket 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.
- Recommendations/Instructions:
- Take the following steps to check for damaged ground wire bonds if the symptoms for 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 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.
- Service Bulletin
- There is a factory service bulletin for the following Chevrolet models:
- 2007-2010 Chevrolet Avalanche
- 2007-2010 Chevrolet Corvette
- 2007-2010 Chevrolet Silverado
- 2007-2010 Chevrolet Suburban
- 2007-2010 Chevrolet Tahoe
- 2008-2010 Chevrolet Silverado Hybrid
- 2008-2010 Chevrolet Tahoe Hybrid
- Chevrolet 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 underhood fuse block for damaged terminals or the poor terminal fit and mispositioned fuses in the 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 a sharp area on the engine block.
Cost of diagnosing the U0101 CHEVROLET code
The cost of diagnosing the U0101 CHEVROLET code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle’s make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
U0101 CHEVROLET 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.
The serial data circuit is how the devices in the vehicle communicate with each other. Once the scan tool is connected to the serial data circuit through the Data Link Connector (DLC), the scan tool can be used to monitor each device for diagnostic purposes and to check for Diagnostic Trouble Codes (DTC). When the ignition switch is in RUN, each device communicating on the serial data circuit sends a state of health message to ensure that the device is operating correctly. When a device stops communicating on the serial data circuit, for example, if the device loses power or ground, the state of health message, it normally sends on the serial data circuit disappears. Other devices on the serial data circuit, which expect to receive that state of health message, detect its absence; those devices, in turn, set a DTC associated with the loss of the state of health of the non-communicating device. The DTC is unique to the device which is not communicating, and one or more devices may set the same code. A loss of serial data communications DTC does not represent a failure of the devices that contain the stored code.