Engine Coolant Temperature Signal Out of Range (Isuzu)
What does P1671 mean?
The P1671 code means the vehicle's onboard diagnostic system has detected: Engine Coolant Temperature Signal Out of Range (Isuzu). This is a moderate severity code.
Common Symptoms
- Check Engine Light on
- Temperature gauge reads maximum or minimum
- Cooling fans running constantly
- Poor fuel economy
- Rich running condition on cold starts
Probable Causes (Ranked by Likelihood)
- Faulty engine coolant temperature sensor Very High
- Corroded ECT sensor connector High
- Open or shorted wiring in ECT circuit Moderate
- Low coolant level exposing sensor Low
Step-by-Step Diagnostic Procedure
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Check coolant level. A low coolant level can expose the sensor tip, causing erratic readings.
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Let the engine cool. Measure ECT sensor resistance and compare to temperature/resistance chart.
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Inspect the ECT sensor connector for corrosion, loose pins, or coolant contamination.
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With ignition on, check for 5V reference at the sensor connector. Missing voltage indicates a wiring issue.
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Compare scan tool ECT reading to actual engine temperature using an infrared thermometer.
Frequently Asked Questions
Can a bad ECT sensor affect my fuel economy?
Yes. The ECU uses coolant temperature to adjust fuel mixture. A sensor reading incorrectly cold will cause the engine to run rich, wasting fuel.
Is the ECT sensor the same as the temperature gauge sender?
On some vehicles they are separate sensors, on others a single sensor feeds both. Check your service manual for your specific model.
How often should the ECT sensor be replaced?
ECT sensors do not have a maintenance interval but typically last the life of the vehicle. Replace only when faulty.