P0118 is a common OBDII trouble code. It is a general code, which means that it’s going to have the same meaning for the Chevy Sonic as it would any other vehicle.
P0118: Engine Coolant Temp Sensor Circuit → High Input
This code is thrown when the resistance coming from the coolant temp sensor does not change as the vehicle warms up.
Chevy Sonic P0118 Symptoms
P0118 is sometimes accompanied by noticeable symptoms. These symptoms include failure to start, rough idle, misfiring, decreased fuel economy, and the service engine soon light.
It’s just as likely that the only sign that you’ll get from the Sonic is the check engine light itself.
As P0118 can greatly affect the drivability of your Sonic, we recommend fixing it as soon as possible.
P0118 Causes: Chevy Sonic
Most of the time, the cause of P0118 is going to be related to the wiring or the sensor in some way or another.
Here’s a great video from CarNToys from YouTube on this exact problem.
Wiring Issue
It’s a good idea to start diagnosing P0118 in your Sonic at the wiring harness. It’s often the reason why the code was thrown. It’s also cheap and easy to diagnose.
Start by inspecting where the harness plugs into the Temp Sensor. After that, inspect the harness for wiring problems. Here’s a great guide on inspecting your wiring harness.
The Sensor Itself
After thoroughly evaluating the wiring harness, it would be time to take a look at the sensor itself. It operates by receiving a 5 volt signal from the computer and a ground. It drops voltage as it warms up. If you’re not getting 5 volts, re-inspect the wiring harness.
If you have a volt meter, you could test the signal coming from it as the engine warms up. If it remains the same, than the sensor is not working properly.
Replacing the sensor straight away isn’t much of a gamble. They’re very affordable.
Other Causes
There can be other causes of P0118 in your Sonic. They typically aren’t going to be as prevalent though. A bad PCM can cause the the code to be triggered.
Engine coolant can cause the code to throw if it gets corroded enough. So, if you find yourself in a situation where you can’t remember the last time that the coolant has been changed, it may be worth a shot to just change it and see if you get lucky.
Conclusion
Most of the time, P0118 is going to be caused by a bad temperature sensor. Wiring issues are the next most likely cause. Good luck diagnosing your Sonic!
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