Rick's Free Auto Repair Advice

U2107 code — What it means and how to fix the problem

Learn what a U2107 code means and how to fix the problem

Because the 2nd position is a “2” it’s a manufacturer-specific code. GM defines a U2107 as Lost Communications with Body Control System. In other words, the engine control module (ECM) can no longer communicate digitally with the body control module (BCM). This is most likely the result of a problem with the data line between the two or a failure of a module on the data bus that’s injecting voltage onto the bus.

Possible causes of a U2107 code

• Faulty BCM
• Loss of power to the BCM due to an open in the power wiring or a blown fuse
• Ground connection failure to the BCM
• Short or open in the wiring harness on either the power, ground, or data bus between the ECM and BCM
• A failure of any other module on the same data bus that’s causing interference or voltage injection onto the bus.

How the data bus works

Vehicle modules connect to either a high-speed or low-speed Controller Area Network (referred to as a CAN Bus) system. The bus is usually shielded to prevent interference and carmakers often install an end-of-line resistor on each data bus.

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. The modules often send periodic messages that must be confirmed by the receiving module to ensure they are online and receiving and transmitting properly. Each message contains the identification number of the transmitter module.

If a module fails to return a confirmation message, the ECM will set a trouble code and turn on the Check Engine light.

How to diagnose the problem

Since the U2107 code indicates a problem with the BCM, start by checking for good power and ground to the BCM. Get a wiring diagram and use a computer-safe test light or DVOM to check for each.

If the powers and grounds are good, locate the data bus and check for broken or chaffed sections on the wiring harness.

If the wiring harness checks out. Connect your scan tool and try to communicate with the BCM. Then locate each module sharing the data bus and disconnect one module at a time until you see communication return. The module that allows communication is the one causing the data bus to fail. If none of the modules is the problem, then the BCM itself is the likely cause.

Symptoms of a bad BCM and U2107 code

• Check Engine light or the service engine soon warning message showing
• Possible issues with instrument cluster data
• Possible issues with remote keyless entry

© 2012 Rick Muscoplat

U2107 Lost Communications with Body Control System (GM specific code)

This GM specific code means that the PCM cannot send or receive data to the body control module. This is most likely the result of a failure in the data line.

© 2012 Rick Muscoplat

Posted on by Rick Muscoplat



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