P0118 Code Meaning and Next Steps

First checks take 10 to 15 minutes for the first checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The engine starts running much worse, stalls, or the warning light flashes.
!The vehicle begins to overheat or lose power sharply while the code is active.

If the light is steady and the vehicle still drives normally: Often yes for a short time, but it should not be ignored.

What to check first

Step-by-step checks

1
Free - no tools
Let the engine cool before touching coolant or cooling-system parts
2
Free - no tools
Check the coolant level and look for obvious leaks or damage near the sensor
3
Basic tool needed
Inspect the ECT connector and harness for corrosion, loose fit, or heat damage
4
Basic tool needed
Compare the live coolant reading to how the engine actually behaves from cold start to warm-up
5
Basic tool needed
If the temperature reading looks unrealistically hot right away, circuit testing becomes more useful than a guess

If the code returns

-If the reading stays high even when the engine is cold, the sensor or circuit is a strong suspect.
-If moving the harness changes the reading, wiring or connector problems move higher on the list.
-If the code returns after a sensor replacement, check the connector pins and reference circuit again.

Background

What this code means

P0118 is a generic OBD-II engine coolant temperature sensor code.

A high ECT signal often means the ECU thinks the engine is hotter than it really is, which can affect fueling and fan control.

A cold engine that seems to warm incorrectly or a gauge that jumps oddly can fit this code.

Diagnosis

Common causes

Most common

Open ECT circuit

A break in the signal path can make the reading jump high.

Common

Failed ECT sensor

The sensor can drift hot internally even when the engine is cold.

Common

Connector or pin issue

A loose or damaged connector can behave like an open circuit.

Possible

Heat or harness damage

A damaged harness near the engine can produce the same fault.

Avoid these mistakes

What not to do

xDo not replace the sensor first if there is an obvious wiring, connector, or intake issue.
xDo not ignore drivability changes just because the code sounds like a sensor problem.

Parts

Parts that may need replacing

PartTypical costNotes

Coolant temperature sensor$15-$70Relevant when the signal is clearly too high and the connector checks out.

Connector pigtail repair$15-$90Worth checking if the plug or pins are damaged.

Harness repair$20-$150Relevant if a wiring open or heat damage is found.

Related OBD codes

P0117

P0117 usually means the engine coolant temperature signal is reading too low.

P0128

P0128 usually means the engine is not reaching the temperature the ECU expects in time.

P0111

P0111 usually means the intake air temperature signal is out of the expected range.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0118 was expanded around common high coolant-temperature signal faults, including open circuits, sensor failure, and harness damage.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0118 - P0118 Usually Means the Engine Coolant Temperature Signal Is Reading Too High