OBD-II Standard U0943: OBD-II Standard OBD-II Universal E...

Symptoms

The engine may not start. Communication with the immobilizer module is lost. DTC U0943 is stored by a control module that lost communication with the Immobilizer module.

Possible Causes

CAN bus wiring to immobilizer fault
Immobilizer power supply fault
Immobilizer internal failure
Key transponder not recognized

Troubleshooting Steps

Step 1: Connect a diagnostic scanner and read all module DTCs to confirm U0943
DTC U0943 is present; note which module logged the code
Step 2: Check CAN bus wiring between the affected modules for continuity, shorts, and termination resistor values
CAN high and low lines intact, 60 ohms across the bus
Step 3: Verify power and ground supplies to the affected module
Battery voltage at module power pin, less than 0.1V drop on ground side
Step 4: If wiring is intact, the affected module may need replacement and programming
Communication restored after module replacement and programming

How to Reset

Clear the DTC after repair using a diagnostic scanner. The code will clear automatically if communication is restored and no fault is detected for 3 consecutive drive cycles.

Common Replacement Parts

varies: Immobilizer module (requires programming) (Confirm part number via VIN before ordering; programming typically required)

Frequently Asked Questions

Q: What does code U0943 mean?
This is a network communication DTC indicating lost communication with the Immobilizer module. The CAN bus wiring, module power supply, and the module itself should be checked.
Q: Can I drive with code U0943?
Driving may be possible but the affected system may not function. If the code relates to ECM, transmission, or brake communication, have it diagnosed promptly for safety.

OBD-II Standard OBD-II Universal Error Code U0943