Cooling system issue, 3 Codes

[pL2005]

I have an 05 Envoy XL 4WD 4.2L. Bought it last May (2015) with about 173k on it. I have 184k on it now. In January I was getting P0128 (Failure to reach operating temperature) so I changed the thermostat. No issues for several months.

Maybe 2 months ago (April?) the temperature gauge started jumping all over the place one day. I read that I probably should have replaced temperature sensor/sender when I did the t-stat, but it never did it again so I wasn't too worried about it.

Last month, I noticed the roaring fan noise when I left the driveway and I got another CEL ( P0495 - Fan Speed too high). I reset the code and it didn't come back. The roaring fan seems to have gotten better, but I still hear it occasionally when first starting the truck.

Finally, fast forward to this week. CEL came on again and it was P0480 (Fan 1 Control Circuit). I've also been noticing the temp gauge boucing around a bit between 1/4 and 1/2 (210). Since I replaced the thermostat in Jan, it has always sat just past 210 (but not quite to the next tick mark). I know the gauge is a little bit of PCM smoke and mirrors, but anyway...... I reset the CEL and it came back about 3 days later, but this time was P0128 (Failure to reach operating temp) again. I reset that and today the CEL came back again. This time it's P0480 and P0128.

I've read a ton of threads on each of my codes, but I haven't found anyone with this combination of the 3. If anyone has any diagnostic advice, I'm all ears. I'm tempted to replace the temperature sensor/sender and fan clutch. While I'm in there I will inspect the wiring harness as I've heard it can rub/chafe and cause the P0480. The thermostat in January was from Autozone. Should I have gone Delco? Should I do the water pump if I do the fan clutch? Finally if I do the fan clutch, should I go Dorman or Delco? I'm paranoid on the ACDelco thing since I had to do my engine mounts twice after the cheap aftermarket parts were junk.

Thanks for your advice.

 

[Sparky]

The needle jumping crazy could be either the temp sensor, or the stepper motor losing its mind. One way to tell would be to use a scan tool to get a second opinion on the temperature. If it jumps too, then the sensor is likely. If it behaves while the gauges bounces, then the stepper motor is losing it. I'm leaning towards the sensor just because you've gotten a temp code again.

Fan clutch sounds like a typical wearing down clutch. Mine was doing that sometimes but never actually threw a too fast code, though it threw a too slow code several times. But before you do that, since you did get a control circuit code, I'd check the harness going to it first just in case you have some chafed wiring that is triggering all that. AC Delco is what you'd want, the Dorman unit has been problematic for several people.

Water pump at the same time - hard to say. If there is no play in it with the belt off and no noise I'd be tempted to leave it simply because I had 215k and mine never missed a beat. But at the same time they aren't all that expensive, so it may make sense to replace it.

I used a Stant thermostat in my TB when my stat started acting up.

 

[Mooseman]

It's ACDelco all the way except for the fan clutch, where Hayden is preferred and cheaper. Dorman is a crapshoot.

But, before condemning the clutch, change the sensor first to eliminate that. If the PCM is seeing bad readings, it may be reacting to that by increasing the fan speed but if you got a fan overspeed code, then the PCM is saying that it is going faster than commanded. There have been instances of failed clutches with a circuit code so unless the wiring is at fault, I'd probably change the clutch while I'm there.

 

[pL2005]

Thanks for the insight. Today the CEL went off on its own. My sense is that the temp sender is bad and maybe the fan clutch as well. I will likely replace them both and probably do the water at the same time and check the wiring harness as well.

If for some reason it's a stepper motor, that's in the instrument panel correct? Are they hard to replace? I've also got an intermittent oil pressure gauge going to 0 when driving (which I think is the oil sender but that has stopped recently), and my PRND321 display is so dim it can barely even be read at night, so I'm wondering if replacing the whole panel with something from a junkyard might be the way to go if it turns out I have stepper motor problems.

Thanks again.

 

[mrrsm]

Having done this myself in error when changing out two different Coolant Temp Sensors on my '93 Chevrolet Camaro Z-28... I made the mistake of putting those two in the wrong locations...even though both threaded into either the Water Pump or the Engine Head. Are the connectors unique enough for this not to happen with GMT360s making this even remotely possible?