What this code means

The PCM has determined the engine is not reaching normal operating temperature within the expected time frame. The coolant temperature is not rising as quickly as it should after a cold start, indicating the thermostat may be stuck open.

Symptoms

• Check Engine Light
• Poor fuel economy
• Heater blows lukewarm air
• Engine runs rich
• Extended warm-up time

Common causes

• Thermostat stuck open (most common)
• Faulty engine coolant temperature sensor
• Cooling fan running continuously
• Low coolant level causing sensor exposure
• Thermostat housing leak

Diagnostic steps

1. Check coolant temperature with scan tool vs infrared thermometer
2. Monitor coolant temp rise over time after cold start
3. Test thermostat operation in hot water
4. Verify cooling fans are not running continuously on cold start
5. Check coolant level

Repair notes

Replace the thermostat if the engine does not reach operating temperature within the expected timeframe.

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