This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.
Definition
U1120 is an OBD-II Code that refers to Lost Wheel Distance Message
Meaning
A U1120 code is a generic communication systems diagnostic trouble code that indicates that there’s a loss of communication the vehicle speed signal over the Controlled Area Network (CAN) C bus from the Anti-Lock Brake System (ABS) Module. When the PCM does not receive a vehicle speed signal from the Anti-Lock Brake System Module over the CAN C bus, it activates an error code.
Causes
Common causes for this code include:
- Communication Issues
- Faulty Controller Area Network (CAN) C Bus Controller Circuit
- Faulty ABS Module
Symptoms
The symptoms of a U1120 code are:
- Engine Light ON (or Service Engine Soon Warning Light)
Diagnosis
To diagnose a U1120 DTC code, a technician would:
- Check for communication issues between modules
- Check battery voltage for proper levels
- Check for communication issues between the PCM and ABS and VSS
- Check DTC's history; see if this is a current or former (resolved) issue
- Check all wiring connections, make sure they’re tight and not corroded.
- Diagnose any other problems found using freeze frame data and check related systems
Common mistakes
The following are some of the most common mistakes that a technician may make when diagnosing a U1120 code:
- Not using the proper diagnostic test equipment
- Not checking freeze frame data and Checking for DTC’s only
- Not following proper repair procedures
- Not using a factory shop manual
How serious is this?
A U1120 code is considered to be an Intermediate level code.
What repairs can fix the code?
The following are solutions that may fix this problem:
- Replace the faulty wire(s)
- Repair any corrosion
- Replace the PCM
- Cleaning and correction of Battery Terminals
- Clearing the code
Related codes
A U1120 is related to and may be accompanied by the following codes:
U1000 – Lost Communication with ECM/PCM
U1010-Lost Communication with Transmission Control Module (TCM)
U1020-Lost Communication With Fuel Pump Control Module
Conclusion
In conclusion, the U1120 code is a communication error between the Powertrain Control Module (PCM) and the ABS Module. The ABS Module is responsible for providing wheel speed information over the Controller Area Network (CAN) C bus, so when it cannot communicate with the PCM, it produces error codes to notify technicians of a loss in communication. The most common causes are corrosion on battery terminals and wiring faults.