What this code means

The Engine Coolant Temperature sensor reading is outside the expected range during the KOEO or KOER self-test. The engine may not be at the required operating temperature when the test was run.

Symptoms

• Check Engine Light
• Poor fuel economy
• Running rich when warm
• Fan may run continuously

Common causes

• Engine not fully warmed up during test
• Faulty ECT sensor
• Thermostat stuck open
• Cooling system issue
• Wiring problem

Diagnostic steps

1. Ensure engine reaches full operating temperature before running self-test
2. Compare ECT reading to actual coolant temperature with infrared thermometer
3. Test ECT sensor resistance vs temperature specifications
4. Check thermostat operation
5. Inspect wiring and connector

Repair notes

Warm engine fully before self-test. Replace ECT sensor or thermostat if faulty.

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