P0118 code: Engine Coolant Temperature (ECT) Sensor Circuit High
P0118 means engine Coolant Temperature (ECT) Sensor Circuit High. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0118 means
The engine coolant temperature (ECT) sensor tells the computer how hot the engine is, which affects fueling, cooling-fan operation, and more. P0118 means that sensor's signal is reading high — which the computer interprets as extremely cold (or an open circuit). Usually it's a failed sensor or a break in its wiring/connector, and occasionally genuinely low coolant. A false "cold" reading makes the engine run rich and may keep the cooling fans from turning on when they should, so it's worth fixing.
P0118 symptoms
- Check-engine light
- Rich running and reduced fuel economy
- Hard starting when warm
- Cooling fans not running or running constantly
- Inaccurate temperature gauge in some cars
What it costs to fix P0118
Typical range: $40–$250 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| ECT sensor | $15–$80 | ~0.3–1 hrs |
| Wiring / connector repair | $10–$120 | ~0.5–1.5 hrs |
| Coolant top-up | $15–$60 | ~0.2–0.5 hrs |
The ECT sensor is inexpensive; cost is mostly access labor, which is low on most engines. Wiring repairs are cheap once the fault is found. A genuinely low coolant level points to a separate leak worth checking.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0118 for my exact vehicle →
How to fix P0118
Easy — basic tools, most owners can do this
- Check the coolant level first
Look at the overflow tank and, on a stone-cold engine only, the radiator. An ECT sensor sitting in an air pocket because coolant is genuinely low can set this code — and low coolant means there's a leak worth finding regardless.
- Sanity-check the live temperature reading
On a cold morning the scan-tool coolant temperature should roughly equal the outside temperature. A reading pegged at the extreme cold end (around -40) while the engine is clearly warmer than that confirms an electrical fault rather than a cooling problem.
- Do the jumper test at the connector
Unplug the sensor and bridge the two connector terminals with a paper clip or jumper wire, key on. If the reading slams to full hot, the wiring and computer are fine and the sensor has failed open — replace it. If nothing changes, the fault is a broken wire or bad connector upstream.
- Repair the wiring or connector if the jumper test failed
Inspect the connector for corroded or backed-out pins and the harness for a break, especially where it flexes or passes near heat. An open circuit here produces the identical false 'extremely cold' reading.
- Fit the new sensor and verify warm-up behavior
Replace the sensor with the engine cool, top up any lost coolant, clear the code, and watch the temperature climb smoothly to operating range. Rich running and hard warm starts should disappear once the computer sees real temperatures again.
DIY or shop? Nearly always a driveway job: the jumper test takes two minutes and tells you definitively whether to buy a sensor or fix a wire, and the sensor itself is inexpensive and accessible on most engines. A shop makes sense mainly if the harness fault can't be found visually, or if the coolant was genuinely low — a hidden leak deserves a proper pressure test.
Tools for the DIY steps: OBD-II scan tool · Jumper wire or paper clip · Socket or wrench for the sensor · Matching coolant for top-up · Wire repair supplies
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0118.
Start a case with P0118 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0118?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0118: common questions
Can I drive with P0118?
Not something a code can answer by itself. A false cold reading can stop the cooling fans from running, raising overheating risk in traffic or heat, so watch the temperature gauge and get it fixed soon rather than letting it ride. If the gauge climbs toward hot, stop driving and shut the engine off.
What does "circuit high" mean for P0118?
The sensor's voltage is at the high end, which the computer reads as extremely cold or disconnected. That points to a failed sensor or an open (broken) wire rather than a real temperature.
Can P0118 cause overheating?
Indirectly — if the computer thinks the engine is cold, it may not switch the cooling fans on when needed. The engine isn't actually cold, so it can overheat. That's why it's worth fixing promptly even though the car runs.
How much does it cost to fix P0118?
Usually inexpensive — the ECT sensor is cheap and easy to reach on most engines, and wiring repairs are modest. Confirm the wiring before replacing the sensor.
Symptoms that trigger P0118
Drivers who get this code often notice one of these. Each has its own causes and cost guide:
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0118 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0118 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.