Applicable Systems
OBD-II
Symptoms
ECT sensor signal indicates coolant temperature below -40C (open circuit); ECM may run rich continuously.
Possible Causes
- ECT sensor signal wire open
- ECT sensor internal open circuit
- Connector disconnected or corroded
Troubleshooting Steps
- Step 1: Check ECT connector is fully seated
Connector engaged - Step 2: Check signal wire continuity
Wire continuity good - Step 3: Measure sensor resistance
Resistance matches temperature - Step 4: Replace ECT sensor if open circuit
New sensor resistance normal - Step 5: Clear code and verify reading
ECT reads normal operating temp
How to Reset
Clear with OBD-II scanner after repair.
Common Replacement Parts
- ECT Sensor (OEM spec)
Frequently Asked Questions
- Q: Why does engine run rich with P0118?
ECM defaults to cold engine strategy (-40C) and enriches mixture for warm-up. This wastes fuel and may cause rough running.
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Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II
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