P2C40: Fan 4 Control Circuit High

What it means

The control circuit of cooling fan 4 reports a control circuit high condition. Fan operation cannot be commanded reliably.

At a glance

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

How it works

Cooling fan 4 receives a control signal through a circuit monitored by the vehicle module. This code indicates that circuit is high, which can result from a wire shorted to battery voltage, an open relay coil, or poor connector contact.

Common causes

Most likely first.

1. Control wire shorted to B+
2. Relay coil open
3. Connector pins corroded - high contact resistance

Symptoms

• Check-engine light
• Engine may overheat in traffic or at idle

How to diagnose it

1. Review freeze-frame data and command fan 4 with a scan tool, if supported, to see whether the circuit fault appears during the command.
2. Inspect the fan 4 control wire for damage or contact with a battery-positive supply, and check connectors for corrosion or loose pins.
3. Check the fan 4 relay coil and socket for an open circuit or damaged terminals using the vehicle wiring information.
4. Test the control wire for a short to B+ and for continuity through the relevant connections per the manufacturer's procedure.
5. Test the relay and control circuit against the manufacturer's specification, then confirm fan 4 responds to a command.

Common fixes

• Clean or repair corroded fan 4 connector and relay socket terminals.
• Repair the control wire where it is shorted to battery voltage.
• Replace the fan 4 relay if its coil is open.
• Repair an open or damaged connection in the fan 4 control circuit.

Can I keep driving?

Fan 4 may not respond properly, so the engine can overheat in traffic or at idle. Avoid heavy loads and monitor engine temperature; stop safely if it rises.