2004 Pontiac Montana - Inaccurate Coolant Temperature Gauge

[mikeyd17]

Hello,

I have a 2004 Pontiac Montana with about 107500 kms on it (VIN: 1GMDX03E24D183870) and the coolant temperature gauge is not working properly. Sometimes when I start my van, the temp gauge is pinned at MAX temp and stays there the whole trip...other times it's pinned at MIN temp...and other times it seems to work OK. When it's pinned at MAX temp, I check the actual temp that the on-board computer is seeing, by using my OBDII scan tool...and I get about 87 degrees C when I'm halfway into my trip (i.e. - when the van is at operating temp), which seems OK. All the other analog gauges are working perfectly.

What could be causing this? Any ideas? I read a lot about the issues with "connector C305" on the Internet on the Montana vans...could this be the problem? Any help would be very much appreciated. Thanks very much in advance.

Mike Durocher
Oshawa, ON
Canada

[rockwood84]

i would start by changing the temp sending unit out and see if it makes the temp gauge work right. if the sender is bad it will make the temp gauge read crazy.

[mikeyd17]

Thanks for your reply.

Where is the sending unit for the temp gauge located?

Does this sending unit do "double-duty"...by sending the on-board computer (PCM) with information for emissions control, and also sending the temp gauge with the proper value?

Or, is there one sending unit for the temp gauge and one temp sensor (ECT) for the on-board computer (PCM)?

TIA

Mike D.

[rockwood84]

the ect [engine coolant temp]sensor is below the fuel regulator the book shows it on the left side of the the thermastat .book is only refering to one.

[farmallcub49]

I am having the same problem. I replaced the sending unit and it isn't any better. The gauge stays pegged out at MAX. There is no air in the lines. The thermostat is working fine as the water is circulating. I used a Raytek heat gun and the temps were all normal. The block near the sending unit read 180 F. I hope it isn't the thermostat, it looks like a bear to change, not near as bad as the spark plugs though!!

[rockwood84]

if you replace the t-stat replace it with one made in usa.if you put a cheap one made in mexico ,you'll end up changing it right back out. the ones made in mexico will not open.to get down to the t-stat the throttle hose has to be removed.and its a little bit aggravating to remove and replace.

[vatechguy3]

i am having the same problem, the water temp gauge is pegged high, no SES lights.

When i turn the key to the "On" position, sometimes i can make the gauge return to the minimum postion by rotatign the key between on and off positions a few times, and then starting the car. then the gauge works fine.

any ideas?

thanks
tony

[mrdiy383]

I had this exact problem with my van. I have to replace the stepper motor in the instrument cluster. An updated version is available on ebay and is only about 10 bucks. If you can de-solder and resolder on a circuit board it is easy to do. If you want more info about this just ask me.

[Streatorboy1948]

I just drove from Detroit to Phoenix and had this problem several times. I also had the fuel gauge doing it. It is definitely the gauges. I can hear the stepper motor indexing with each key on and the needle comes to rest at a differnt point each time. I will pursue the fix suggested.

[mrdiy383]

Originally Posted by Streatorboy1948

I just drove from Detroit to Phoenix and had this problem several times. I also had the fuel gauge doing it. It is definitely the gauges. I can hear the stepper motor indexing with each key on and the needle comes to rest at a differnt point each time. I will pursue the fix suggested.

If you do this, make sure to replace all 3 motors, your fuel guage and speedometer are prone to failure as well. They all use the same motor (x25.168). Also be sure to mark the position of the needles before removing them. Good luck.

[Streatorboy1948]

Thanks, I agree since the work is taking it out. I might just look for a reworked assembly. My nephew did that for his GMC Sierra and another did it for his Tahoe. It must be pretty comon.

[mrdiy383]

Originally Posted by Streatorboy1948

Thanks, I agree since the work is taking it out. I might just look for a reworked assembly. My nephew did that for his GMC Sierra and another did it for his Tahoe. It must be pretty comon.

I think if you put a different assembly in, you will lose your correct milage. I bought my stepper motors on ebay.

[Streatorboy1948]

Yep. I thought the same after I posted. Will repair myself or remove the unit and let someone else do it. My nephew used www.autoecu.com for his truck and got a quick turnaround, but I will have to check them out. I have no knowledge of them.

[andypapa]

Hi , I'm new to the forum. I have the same temperature gauge problem on my Montana. I already replaced the sensor and the problem came back. Did replacing the stepper motors fix the problem?
André
Beloeil, Québec

[Streatorboy1948]

It is almost definitely the stepper motor in the instrument cluster. They are very cheap. Since they cycle every time you key on, all four guages wear out at about the same time. I took my 2004 Montana to a speedo shop and he replaced them all in about 1.5 hours. You can also take the cluster out and either unsolder and replace the motors yourself or send it for repair. This is common not only with GM U vans, but also GM trucks and other cars of this vintage.