What does it mean?
U1039 is a Network (CAN bus, module communications) fault code. It indicates: Data Circuit Malfunction .
Symptoms
- Speedometer reading zero, sticking or jumping around
- Cruise control unavailable and the transmission shifting harshly
- ABS, stability and traction lamps on
- Power steering assist feeling wrong at speed on systems that use vehicle speed
- Automatic door locking, wipers or audio volume that depend on speed behaving incorrectly
- Odometer not accumulating distance correctly
Likely causes
- Vehicle speed sensor or wheel speed sensor circuit fault at the source of the message
- Break, high resistance or short in the serial data wiring between the sending module and the receiver
- Corroded connector or a damaged splice pack on the data circuit
- Transmitting module without power or ground because of a fuse, relay or corroded earth
- Damaged twisted pair, for example an untwisted repair section that has picked up interference
- Aftermarket accessory such as a tracker or speed limiter spliced into the speed signal circuit
- Failed transmitting module unable to build a valid speed message
How to fix it
- Compare the speed value seen by different modules in live data to find where the signal is lost
- Inspect the speed sensor at its source, along with its connector, air gap and drive gear where fitted
- Check the serial data wiring for continuity, shorts to ground and shorts to battery voltage between sender and receiver
- Inspect any splice pack or connector shared by the circuit for corrosion and spread terminals
- Verify power and ground at the transmitting module, using voltage drop tests rather than continuity alone
- Look for aftermarket devices tapped into the speed circuit and disconnect them for a retest
- Repair damaged wiring keeping the correct twist and shielding, then clear the code and road test
- Replace the failed sensor or transmitting module only after the circuit has been proven sound