What it means
A control module has stopped receiving expected messages from the front differential control module. Front differential functions managed by that module may be limited or unavailable.
How it works
The front differential control module communicates with other vehicle modules over the data network to manage front differential functions. U0135 sets when a module does not receive expected messages from that front module, so its controlled functions may be limited or unavailable.
Common causes
Most likely first.
- Front differential control module power or ground fault
- Damaged network wiring or connector
- Front differential control module failure
- Low system voltage
Symptoms
- Drivetrain or chassis warning
- Front differential functions may be unavailable
- Other communication codes
How to diagnose it
- Scan all modules and review freeze-frame or event data to see whether U0135 appeared with low-voltage or other network faults.
- Check battery condition and charging-system operation because low system voltage can interrupt module communication.
- Inspect the front differential module connector and nearby network wiring for looseness, corrosion, water, or physical damage.
- Use a wiring diagram to check the front differential module's power and ground circuits under load against the manufacturer's specification.
- Check the network wiring to the front differential module for opens, shorts, or poor connections using the manufacturer's diagnostic procedure.
- If power, ground, and network wiring are sound, verify whether the module responds to a scan tool before considering module replacement or programming.
Common fixes
- Restore battery or charging-system performance if voltage is low.
- Reconnect or repair a loose, corroded, or damaged front differential module connector.
- Repair an open, short, or damaged network wire serving the front differential module.
- Repair the module's power or ground fault.
- Replace and configure the front differential control module if it remains unresponsive with sound circuits.
Can I keep driving?
If the front differential warning is on or its functions are unavailable, avoid demanding off-road use, hard acceleration, or slippery conditions that rely on those functions. Have the fault checked soon; driving behavior may change if the front differential is not being controlled as intended.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.