P2CB9: Fan 2 Underspeed

What it means

Cooling fan 2 runs below the calibrated minimum speed for the commanded duty. Mechanical resistance high or motor weakened.

At a glance

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

How it works

Cooling fan 2 helps move air through the radiator and condenser when commanded by the control system. This code sets when fan 2 turns more slowly than expected for its commanded duty, which can reduce cooling especially at idle or low road speed.

Common causes

Most likely first.

1. Fan motor bearing worn
2. Supply voltage low under load

Symptoms

• Check-engine light
• Engine temperature may rise, especially at low speeds or while idling

How to diagnose it

1. Check freeze-frame data and live fan command and reported speed to identify when fan 2 falls below its expected speed.
2. With the engine off and cool, inspect fan 2 blades and shroud for debris, damage or contact that could add resistance.
3. Check fan 2 motor connector, fuse and wiring for corrosion, looseness or heat damage.
4. Measure voltage at fan 2 while commanded on and compare it with the manufacturer's specification.
5. If supply voltage is correct, check the fan motor for bearing drag or a weakened motor.

Common fixes

• Remove debris or correct shroud contact restricting fan 2.
• Repair loose, corroded or damaged fan 2 wiring and connections.
• Replace a failed fan 2 fuse after finding the reason it opened.
• Replace fan 2 motor if it remains slow with correct voltage and free blade movement.

Can I keep driving?

Watch the temperature gauge and avoid prolonged idling, slow traffic and towing if engine temperature starts rising. Stop safely if the engine overheats, since continued driving can cause serious engine damage.