What does P0118 mean?
The coolant temperature sensor signal voltage is too high — usually an open in the signal wire, a disconnected sensor, or a failed sensor reading open internally.
Quick Decision Guide
- Disconnected or damaged ECT connector
- Open in ECT signal wire
- Failed coolant temperature sensor (open internally)
When to stop driving
P0118 is rarely an emergency. Drive cautiously and avoid extended idling, since the engine may run rich. Resolve within a week.
Reviewed by ratchit Automotive Solutions for clarity and inspection-first safety framing. Not a substitute for professional diagnosis.
Repair Decision & Cost Guide
Use this guide to decide what to inspect first, what it may cost, and when to move from DIY checks to professional diagnosis.
P0118 affects warm-up performance — confirm the actual coolant temperature with a scanner before replacing the thermostat or sensor.
DIY vs. Shop
Can you keep driving?
Best first DIY check
Don't replace this first
When to seek a shop
Recommended next action
Estimated Repair Cost
Inspection cost
$0–$25 DIY scanner
Shop diagnostic cost
$80–$150 (typical shop diagnostic fee)
Shop repair cost
$80–$250
Diagnostic uncertainty: This code points to a system or condition, not a guaranteed failed part. Inspect before replacing.
Cost variation: Costs vary by vehicle, location, part quality, labor rate, and the confirmed root cause.
Inspect Before Replacing
These checks are cheap, fast, and rule out the most common causes before spending money on parts.
- 1Inspect the ECT sensor connector — reseat if loose, repair if damaged.
- 2Clear the code and recheck — many P0118 cases are simple connector issues.
Track this cooling issue
Save this issue to My Garage, track what you inspect, and build service history for this vehicle.
V-IQ readiness preview: Medium impact — resolving and tracking this issue may improve your V-IQ readiness. Tracking active codes and resolutions builds a service history we use to estimate V-IQ readiness over time.
Understanding P0118 in detail
P0118 is the inverse of P0117. Because the ECT sensor is an NTC thermistor, a stuck-high voltage corresponds to the ECM seeing an extremely cold reading (often -40 °F). This causes prolonged cold-start enrichment, slow closed-loop entry, and high idle. The most common cause is an open in the signal wire, a disconnected sensor, or a sensor that has failed open internally. Repair priority is connector check, wiring continuity test, then sensor replacement.
Symptoms of P0118
- Check engine light on
- Engine runs rich, especially at startup
- High idle that does not drop
- Cooling fans may not run
- Temperature gauge may read low or pegged cold
Common causes
- Disconnected or damaged ECT connector
- Open in ECT signal wire
- Failed coolant temperature sensor (open internally)
How to diagnose P0118
Steps ordered by urgency — tackle Now items first.
- NowInspect the ECT sensor connector — reseat if loose, repair if damaged.
- NowClear the code and recheck — many P0118 cases are simple connector issues.
- SoonTest signal wire continuity from the sensor connector to the ECM with a multimeter.
- LaterReplace the ECT sensor if wiring checks good.
How to fix P0118
Fixes listed in order of likelihood and cost-efficiency.
- 1Repair ECT connector or wiring
- 2Replace coolant temperature sensor
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Recommended tools & parts
These recommendations appear because this issue commonly requires inspection in this system area. ratchit does not recommend replacing parts until the likely cause is confirmed.
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Estimated Repair Cost — P0118
Ranges vary by vehicle, region, and shop. Use as a ballpark — always get a quote.
DIY estimate
$10 – $40
Shop estimate
$80 – $250
DIY estimate
$15 – $50
Shop estimate
$100 – $250
Cost data is estimated and may not reflect your specific vehicle or location.
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Frequently Asked Questions
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