Ryans99ls1

iTrader: (16)

Ok so my car threw a P0118 (Engine Coolant Temperature Sensor High Voltage code) this morning. It started just fine, noticed the code, and i drove it to the end of my street and had the code pulled. Bought a new sensor, replaced it and my temp gauge was still at zero after i started it. Figured id try reseting the pcm and now it wont turn over. it cranks, but will not start. Even with the new sensor in the head, i tried plugging in the old sensor and starting it but still no luck.

some background info, the car NEVER did this before i swapped the heads. I put the new heads on and after i bled the system i was driving it and the temp gauge started going crazy and then the gauge would just shut off. I figured i had air in the system, so i bled it a few more times. Drove the car for a few weeks(a 500mi roadtrip too) and it was fine. It started acting up again recently. the temp gauge would fluctuate a lot, the car would sputter and die but it would always start up again. once the temp gauge stopped going nuts, the car ran like a champ. once it finally threw a code, the car ran great but the fans were always on.

i put a tester on it(the pigtail) and its getting ~5v from the pcm. i put the old sensor in hot water and its resistance does change with diff temp water. the wires dont seem to be frayed anywhere either, im lost on this one.

Ryans99ls1

iTrader: (16)

got the car started but still no temp gauge. Check engine light hasnt come back on but im sure it will next time i start it. Fans are both on too

i unplugged the sensor with the car running, put the old sensor in a hot cup of water and plugged it in, no movement on the gauge. wiggled everything, no movement.

1 FMF

iTrader: (1)

since you mentioned you swapped heads it seems logical you pinched a wire, sounds like you have a ECT wire that goes to the pcm pinched somewhere and it's shorting to ground. That would cause the PCM to think the coolant is hot and would trigger the radiator fans to come on and also I think it will prevent you from starting the engine since the PCM thinks there is an overheat condition.

Ryans99ls1

iTrader: (16)

I completely agree with you. But ive checked the back of both heads and there is nothing pinched. ive pulled most of wire loom free and still nothing. The car starts fine now too.

if i rewire the sensor do i have to run the ground from the sensor back to its place in the pcm or can i ground it somewhere else?

1 FMF

iTrader: (1)

i think the ect sensor is 2 wire and the pcm supplies 5v on one wire into the sensor and the return wire goes back to the pcm as a signal. It's not like the old days where the temp sender grounds into the engine block. Shoot me a pm later this evening to remind me and i can look up the wiring in my service manual if someone else doesn't verify that.

1 FMF

iTrader: (1)

the other thing you might consider trying is unplugging the connector to the ect sender and get a resistor of around 80 ohms. I don't remember off hand the resistance range of the sender but the operating range is fairly low. Manually connect that to the connector and see how the temp gauge responds with just turning the ignition key on but not starting the engine. if possible put a scan tool on the obd2 port and monitor ECT temp that the computer thinks it's seeing, this can help rule out whether it's a wiring problem from the sender to the pcm or if it's a gauge problem.

Ryans99ls1

iTrader: (16)

Ok thats what i thought. the last thing i wanna do is re-pin it. Im gonna try a new male pigtail. maybe all the coolant that spilled out corroded the inside of the sensor.

but yeah if you could send me the wiring thatd be awesome.

I reallllly doubt its the gauge. it was working fine before and never showed signs of failing, not ruling it out though. If the car is acting up when the gauge fluctuates, its gotta be the signal wire going back to the pcm.

Thanks for the help so far man.

TA1364

iTrader: (11)

I had a similar problem, the ground wire was the cultprit inside the connector at the temp sensor.

Ryans99ls1

iTrader: (16)

yeah once i replace the male side of the connector ill be able to tell if its actually the wiring behind it, going to the pcm. im going back in a 2 weeks, ill be sure to post the results

TA1364

iTrader: (11)

Something else I did that tested to make sure everything was working correctly is unplug the connector and jump the power and ground, I used a paper clip, and it should throw a p0117 code. If you cant get this code then its a wiring problem.

Ryans99ls1

iTrader: (16)

Just in case anyone else has this problem and stumbles across this thread, i cut the old (male) pigtail out and soldered in a new one(from rockauto) and its fixed.

Im thinking that when i did my head swap, coolant got into the connector and corroded the inside, never checked before i threw it out but its all good now.