tdogg

Hello all,

Long time lurker, possibly first time posting.

I have a weird issue with my GMT900 Suburban 2500. The engine temp sensor on the display will fluctuate between 160 (off) and 210 (normal temp) while driving down the road. Literally I can be driving to work or home (~10 miles) and it will go from working to not working several times. When it isn't working, the DIC will give an error Engine Overheated, Shut off A/C or something to that effect. This gets really frustrating as the A/C is not allowed to run, not an issue in the winter but as we move into summer it is an issue. If it stays off for long enough it will throw a code P0128 for the temp sensor.

Weird thing is that I hooked up my BlueDriver scanner tool and it doesn't register any changes to the coolant temp while using the live data monitoring the engine temp? The instrument cluster will read off and the blue driver live data will continue to read the correct engine temp. I initially thought maybe I had a body control module issue but I just found the thread discussing the issues with the instrument cluster soldering the Q16 transistor to fix dim/failed lighting and was wondering if that is my issue? How could the instrument cluster cause it to throw the P0128 code though?

I'm at a loss and don't know where to start with this intermittent failure. I can't replace this vehicle as there isn't anything out there that does what this paddy wagon does, haul people and gear. Any ideas and help is appreciated in advance!

Work done to date:
Replaced temp sensor with OEM
Pulled all ECM connectors, cleaned and dielectric greased.
Took to dealership for airbag recall (finally) and had them scan and diagnose but they didn't listen and wanted to start with the temp sensor harness ($400 + labor, said no thanks)

-Make: Chevrolet
-Model and Year Model: Suburban 2500 LT
-Drivetrain Layout (2WD, 4WD): 4WD
-Engine Size: 6.0L

Cheers,
Toby

Cusser

Make sure ALL the air is bled out of the cooling system. 10 mile drive in Flagstaff weather is short hop.

Silverfox103

Hi Toby

Like Cusser said, make sure the air is out of the system. The front of the Suburban should be elevated. Maybe worth changing the thermostat.

I've never had this problem since I've owned my Yukon XL for 6 years. But I've owned GM LT1 cars for the best part of 30 years. The following may or may not apply, but here goes: with the LT1 based engines there are 2 sensors that are very confusing to people. The temperature gauge sensor is located on the passenger head. The sensor for the PCM is in the water pump area. People assume the sensor that controls the PCM controls the temp gauge, it does not. Like I said it may not apply to your 2009 Suburban.

As Cusser said, start with bleeding the air, then maybe the thermostat.

Tom

tdogg

Coolant level isn't an issue. Just got back from towing the boat to lake Powell. Thankfully the Burban didn't lose the temp reading and we had ac the whole time.

It's weird that when I tow it doesn't seem to flair up as frequent. I also noticed this trip that the ac wasn't moderating the climate control as normal, it was blowing ice cold air even when I turned up the cabin temp set point. It just changed the fan speed and not the air temp. It has done some other weird things like failed to connect Bluetooth to my phone randomly and random lights in the cabin on. That is why I thought it may be a body control module failing?

I should state this is a daily driver and it also has a cold case radiator with a black bear tune. It has been an issue for over a year now.

That's interesting and a thought I had wondered about if there could be a separate sensor that has failed. I replaced the temp sensor on the passenger head originally. I will have a look at the water pump area to see if there is another sensor down there. Thanks!

Toby