What this code means

The PCM has activated the Fail-Safe Cooling (FSC) strategy because the Cylinder Head Temperature sensor detected dangerously high engine temperature. The PCM alternately disables fuel injectors to use cylinders as air pumps for cooling. The A/C is disabled, and the engine may enter limp mode or shut down entirely. This is a severe code — continued driving risks catastrophic engine damage including warped cylinder heads and blown head gaskets.

Symptoms

• Severe loss of power
• Engine running extremely rough (cylinders deactivated)
• A/C shuts off
• Temperature gauge pegged high
• Engine may stall and refuse to restart
• Limp mode activated
• Transmission may enter limp mode

Common causes

• Low or no engine coolant
• Failed thermostat stuck closed
• Failed water pump
• Clogged or damaged radiator
• Failed cooling fan or fan relay
• Blown head gasket
• Faulty CHT sensor (false trigger)
• Exceeded towing or load capacity
• Damaged wiring to CHT sensor

Diagnostic steps

1. DO NOT continue driving — pull over safely
2. Allow engine to cool completely
3. Check coolant level (do NOT open cap when hot)
4. Check for visible coolant leaks
5. Verify cooling fans operate when engine is hot
6. Test thermostat operation
7. Pressure test cooling system
8. Test CHT sensor resistance vs temperature chart
9. Check for head gasket failure (exhaust gases in coolant)

Repair notes

STOP DRIVING IMMEDIATELY. Allow engine to cool. Top off coolant if low. Diagnose and repair cooling system failure. If head gasket is blown, engine rebuild or replacement may be necessary. If CHT sensor is faulty, replace sensor.

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