What it means
A receiving module detected implausible data from the second engine/powertrain control module (ECM/PCM B — used on V-engines with one ECU per bank or master/slave architectures). Engine torque, RPM or load values fail plausibility checks and are rejected.
At a glance
- Usually lights the warning light of the system that lost communication
- Affects emissions; the car can fail an emissions test
- The engine or gearbox may go into limp mode
How it works
ECM/PCM B is the second engine or powertrain control module where the vehicle uses one, and it shares engine data such as torque, speed, or load with other modules. U0442 sets when a receiving module rejects data from this second controller as implausible; it does not point to ECM/PCM A by itself.
Common causes
Most likely first.
- Module internal fault or sensor input drift
- Software version mismatch after replacement
- Gateway module routing CAN messages incorrectly
Symptoms
- Multiple warning lights may illuminate
- Affected modules may go into limp mode or shut down
- Specific functions inoperative depending on module
- Diagnostic tools may show communication faults
How to diagnose it
- Scan all modules and save freeze-frame data and communication codes, confirming that ECM/PCM B is present and identifying the module that rejected its data.
- Compare live engine speed, load, and torque data reported by ECM/PCM B with ECM/PCM A and other available readings.
- Inspect ECM/PCM B connectors, grounds, power connections, and network wiring for damage, looseness, or corrosion.
- Check for gateway or bus faults that could disrupt messages from the second controller.
- If ECM/PCM B or related modules were replaced or programmed, verify compatible software and configuration, then test the modules and network using the manufacturer's procedure.
Common fixes
- Repair a loose or damaged ECM/PCM B connector, power, ground, or network connection.
- Correct a gateway or bus fault confirmed to affect ECM/PCM B messages.
- Update or configure replacement ECM/PCM B software to match the vehicle's architecture.
- Repair an input or internal fault in ECM/PCM B confirmed by diagnostic testing.
- Replace ECM/PCM B only after wiring, network, and configuration causes are ruled out.
Can I keep driving?
Because the second powertrain controller's data may be rejected, reduced power or other engine warnings can occur; avoid hard acceleration and do not drive if response is erratic or power is severely limited. Arrange prompt diagnosis, especially if additional powertrain warnings appear.
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.