Hi all, I have a 2003 Honda Civic which periodically throws the CEL light on with a P0117..

Symptoms:
The engine will be at normal temps, than occasionally jump to HOT very quickly, than jump back down to normal a minute later.

Diagnosis:
-Failing ECT sensor
-Failing water pump
-Possible short between signal and ground in ECT wiring harness

Repairs:
Ive replaced the ECT sensor and the problem persists... could it be the signs of a failing water pump?
I'm not really sure how to go about checking the wiring since it's sporadic, it's hard to say if maybe wires are too close and melting the insulation shorting them. Is there any place I can just buy a new harness for the ECT to PCM?

Thanks all!! I appreciate everyone's help in advance as I'm not the most knowledgeable about this type of stuff!

 

I'm now thinking it could be a thermostat that needs to be replaced that perhaps periodically gets stuck? That would make the most sense to me and for $20 and a pretty simple repair, I guess I'll have to try it... Hope it works!

 

First make sure the radiator is completely full, check that with the engine cold. Don't just look in the plastic tank, it can be full though the radiator and engine aren't.

Replacing the thermostat is then the next thing to do when you have random overheating, because they do sometimes randomly stick closed like you said.

 

Another symptom is that the engine revs higher than usual at idle... maybe because its trying to get more coolant circulating when the thermostat is blocking it?

Going to check radiator fluid MK378, hope its something as easy as that!

 

The reason why I feel it may not be the thermostat is because on a day when it is 30 degrees Fahreneheit, I start the car and sometimes see the temp gauge immediately spike to hot... At this point the engine, coolant etc is not even warm, nevermind being hot... This leads me to it being low coolant in radiator, or a wiring short, but it's rather odd it happens sporadically...

 

Did you replace the right sensor? I think there are two, one on the engine and one on the bottom of the radiator. The one on the radiator only controls the fan.

 

The fans do turn on and off, so I think it may not be the one on the radiator... I did see a sensor located on the thermostat housing? Is this the sensor you are talking about? What is the sensor called?


Oh , btws I have already replaced the Engine Coolant Temperature Sensor (ECT) so I hope this is a different sensor you are talking about on the engine block.

 

So here is the deal:
Replaced timing belt, water pump, ECT Sensor, thermostat and thermostat gasket.

On cold start:
Car showed HOT on temperature gauge
Unplugged ECT Sensor, and car showed middle of gauge.
Plugged ECT sensor back in, car showed low.

I think based on this info it's safe to say I have a wiring issue ...

No idea how to debug these, since its so sporadic and I have no idea how to see the terminations of the two wires. Any advice?