P0117 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 fully before opening the cooling system or touching hot components
2
Free - no tools
Check the coolant level first, because low coolant can distort the sensor reading
3
Basic tool needed
Inspect the ECT connector and harness for corrosion, damage, or a loose fit
4
Basic tool needed
Compare the live coolant reading to the actual engine temperature after warm-up
5
Basic tool needed
If the engine also has thermostat or cooling-system codes, treat those as part of the same fault pattern

If the code returns

-If the reading stays too cold after the engine is fully warm, the sensor or circuit becomes more likely.
-If the code clears when the harness is moved, wiring deserves a closer check.
-If the code returns after topping off coolant and checking the connector, sensor testing comes next.

Background

What this code means

P0117 is a generic OBD-II engine coolant temperature sensor code.

A low ECT signal often means the ECU thinks the engine is colder than it really is, which can change fueling and warm-up behavior.

Hard cold starts, poor fuel economy, or a gauge that seems too cold can appear with this code.

Diagnosis

Common causes

Most common

ECT sensor short

The sensor can report colder than reality if it has failed internally.

Common

Low coolant level

The sensor may not be properly immersed in coolant if the level is low.

Common

Connector or harness issue

A wiring fault can make the signal look too cold.

Possible

Thermostat or warm-up problem

An engine that genuinely warms too slowly can help trigger the code.

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 sensor signal is clearly low and coolant level is normal.

Thermostat$20-$80Worth considering if the engine really is warming too slowly.

Coolant repair or top-upVariesNeeded if low coolant is the actual cause.

Related OBD codes

P0118

P0118 usually means the engine coolant temperature signal is reading too high.

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). P0117 was expanded around common low coolant-temperature signal faults, including shorted sensors, low coolant, and wiring issues.

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

P0117 - P0117 Usually Means the Engine Coolant Temperature Signal Is Reading Too Low