2015 Yukon XL temp gauge at 0 and radiator fan running constantly

[dorlow]

So, we just drove home and I was noticing as we were driving, the radiator fan was really loud. As we got closer to home, I noticed the temp gauge was basically all the way to cold like the car wasn't running. I was told once that the temp of the engine is measured by coolant and, if you don't have coolant, the car will read cold yet overheat. But, I opened the hood. The radiator overfill has plenty of coolant. The engine wasn't hot at all. It wasn't like I opened the hood and tons of heat was present. But, the radiator fan ran for probably 5 minutes after I shut off the truck. I'm thinking maybe the thermostat... but why wasn't the engine burning hot when I opened it if the thermostat was stuck closed? Any ideas what this is?

[Stealthee]

Your thermostat could be stuck open or and probably more likely your coolant temp sensor has failed. When it fails the ecu goes into a protect mode and acts as if the engine is overheating.

[Blue Bowtie]

Originally Posted by Stealthee

... your coolant temp sensor has failed.

That's the first place I would look. Unplug the CTS and measure the resistance to ground. The indication should be reasonably close to this:

[dorlow]

If the temp sensor had failed, shouldn't it have thrown an error on the dashboard?

[dorlow]

Where is the temp sensor?

[Stealthee]

Originally Posted by dorlow

If the temp sensor had failed, shouldn't it have thrown an error on the dashboard?

Not necessarily.

Originally Posted by dorlow

Where is the temp sensor?

It's on the front of the engine. I found a YouTube video of a 16 XL with the 6.2. The guy talks about what happened and his symptoms are exactly the same as yours and he shows where is is and talks about the disconnection process.

https://www.youtube.com/watch?v=LPVYpqSLnn8

[dorlow]

Ok, so I replaced the coolant temperature sensor and the problem is still there. Now my check engine light is on. I plugged my scan tool into the car and I have 4 codes. P0118 Engine Coolant Temperature Sensor Circuit High Voltage PERMINANT P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating P0118 Engine Coolant Temperature Sensor Circuit High Voltage PENDING P0118 Engine Coolant Temperature Sensor Circuit High Voltage CONFIRMED

[dorlow]

Ok, just watched a Youtube video and it says sometimes I need to manually erase the code. So, I'm going to go try that.

[dorlow]

Ok, so for whatever reason, my scan tool could see the code but I kept telling it to erase the codes and it would tell me 2 codes remain or something like that. I think it said 5 and then kept decrementing. It was only deleting one code at a time. But, then it got down to 2 and wouldn't go any lower. Seems like even if the problem was still there, it would delete the code and the next time the car started up, it would then re-fire the code. But, I was thinking maybe I don't have a good enough scanner. So, I was going to drive it to autozone to see if their tool could do it or buy a more expensive scanner. But, on the way there, I noticed the fan turned off and the temp gauge started working. I know cars usually clear codes themselves when the problem is fixed and you drive it for a little bit. So, I guess that worked here. So, I think I'm set. Thanks all!

[Blue Bowtie]

Even with the engine off/ignition on, if the PCM does not detect a correct range signal an error code will be set. If you got it to clear, that is good. If it repeats, check the connections to the CTS and wire harness.

BTW - I saw that your Griffins dropped a 19U Tier II final round game to Boston yesterday. They had a really good run up to that point.

[dorlow]

So, I replaced the coolant temp sensor when I made this post and it fixed the problem. But a half a year later, it's broken again? Coincidence or is something else causing it to fail?

[Blue Bowtie]

You can measure the resistance of the CTS, and while in there inspect the sensor's connector and wire harness.

[dorlow]

Ok, so replaced the coolant temp sensor again and it's back running normal again. Weird it went bad so quickly.

[dorlow]

Originally Posted by dorlow

Ok, so replaced the coolant temp sensor again and it's back running normal again. Weird it went bad so quickly.

So, lasted a few weeks and broke again. ill have to look at the resistance. So, if the resistance is outside normal, how do i fix it? I looked at the harness a few weeks ago and it looked good to me...

Also, how do I read the chart? I'll be working on the car when it's the temp outside, so the engine will be about the temp is outside. So, it's usually around 40-60 degrees everyday. That would put me in the 40 - 70 degree range which would read 7500 - 3400 ohms. That's a pretty big range.

[aleekat]

Originally Posted by dorlow

So, lasted a few weeks and broke again. ill have to look at the resistance. So, if the resistance is outside normal, how do i fix it? I looked at the harness a few weeks ago and it looked good to me...

Also, how do I read the chart? I'll be working on the car when it's the temp outside, so the engine will be about the temp is outside. So, it's usually around 40-60 degrees everyday. That would put me in the 40 - 70 degree range which would read 7500 - 3400 ohms. That's a pretty big range.

You're reading the chart wrong. It's not outside temp, it's the temp of the coolant. Just Google how to test a coolant temp sensor. I use a bowl of water cold, then hot measuring the water temp.