P2C42: Fan 4 Performance/Stuck Off

What it means

Cooling fan 4 is commanded on but does not produce the expected airflow. Mechanical seizure, broken motor, or relay failure.

At a glance

• Usually lights the check-engine light
• The engine or gearbox may go into limp mode

How it works

Cooling fan 4 moves air through the radiator or another heat exchanger when the control module commands it on. This code means the commanded fan 4 is not producing the expected airflow, pointing to a seized or failed motor, an ineffective relay, or an obstruction.

Common causes

Most likely first.

1. Fan motor seized or burned out
2. Fan relay contacts oxidised
3. Carbon or debris buildup preventing free movement

Symptoms

• Check-engine light
• Engine may overheat in traffic or at idle
• Cooling fan may not run when needed

How to diagnose it

1. Review freeze-frame data and use a scan tool, if supported, to command fan 4 on while checking whether it spins and moves air.
2. With the ignition off and the fan safe to inspect, look for debris or damage that stops fan 4 from turning freely.
3. Inspect fan 4's connector and wiring for loose or corroded contacts and check the relevant fuse and relay.
4. If the fan does not run, test for power and ground at the fan 4 motor during a commanded-on condition using the manufacturer's procedure.
5. If power and ground are present, test the fan motor; if not, check the relay contacts and supply circuit.

Common fixes

• Remove debris that is preventing fan 4 from turning freely.
• Clean or repair oxidised relay or connector contacts.
• Replace the fan 4 relay if its contacts fail testing.
• Replace the fan 4 motor if it is seized or fails its electrical test.

Can I keep driving?

Without fan 4 airflow, the engine may overheat in traffic or at idle, and reduced-power operation may occur. Avoid congestion and heavy loads, watch the temperature gauge, and stop safely if it rises.