What does it mean?
U1071 is a Network (CAN bus, module communications) fault code. It indicates: Data Circuit Message .
Symptoms
- Check engine light (MIL) on together with warning lamps in other systems
- Gauges fed by engine data, such as coolant temperature, reading incorrectly or not at all
- Cooling fans running constantly or not starting when they should
- Rough running, poor throttle response or reduced power
- Automatic transmission shifting badly because it has no reliable engine load data
- Several sensor related codes stored alongside this communication code
Likely causes
- Fault in one of the engine sensors whose value is shared over the network, so the message contains out-of-range data
- Engine controller unable to build a valid message because of an internal fault or missing sensor reference voltage
- Open circuit, high resistance or short on the data line between the engine controller and the receiving module
- Corroded engine bay connector or a damaged splice on the data circuit
- Poor engine controller ground distorting the transmitted data
- Chafed harness on the engine, allowing intermittent corruption under vibration and heat
- Software or configuration mismatch after a module replacement or an engine repair
How to fix it
- Read codes in all modules and address any stored engine sensor faults first, since they are often the source of the invalid message
- Compare engine sensor values in live data with what the receiving module reports, to see where the data becomes implausible
- Check the sensor reference voltage supplies from the engine controller, as one shorted sensor can pull down a shared reference
- Inspect engine bay connectors and splices for corrosion, heat damage and chafing
- Test the serial data circuit between the modules for continuity, shorts to ground and shorts to battery voltage
- Do voltage drop tests on the engine controller grounds
- Verify module software and configuration after any recent repair or replacement
- Repair the faulty sensor or wiring first, then clear codes and confirm the shared data is now valid