Temperature Gauge/Electrical Mystery

[shoto]

Just signed up as a new member and need some advice. I'll try to be succinct with explaining this but you'll need some details (after all it is probably electrical in nature).

I have a 2004 GXP with approx. 34,000 miles.

The temp gauge climbed suddenly (pegged out on max!!) on a recent drive. Pulled it over, engine temp did not seem abnormal but I didn't take any chances. I let it cool and got it home: no coolant leaks, coolant level normal, belts ok, no noise from water pump etc.

I carefully drove it to my mechanic thinking it might be a stuck thermostat or bad coolant temp sending unit. Gauge only went to 200 on the drive over to the shop. Mechanic got normal reading from gauge and actual engine temp (infrared thermometer) while running engine in the shop. He then took it out on the road and temp gauge spiked again. He again checked actual engine temp with his thermometer and engine was normal 190 degrees.

Mechanic said that with the computer analysis he can do with his equipment he was able to determine that the computer was sending the correct data to the instrument cluster since the oil pressure, and whatever else it sends, was correct. He says the same data line is used for that info and the engine temperature therefore the computer is good and the data line is good. So it must be a bad temp gauge. Replacement cost is $440.

It all makes sense so far. I asked if there was any way to determine for sure if the temp gauge is faulty. Who wants to spend $440 on a guess? He said the only way is for a GM dealer who has the specific computer for the diagnosis to do it (more diagnostic $). He said he is 99% sure that the gauge is bad.

Thought about this for awhile and talked to him about the lights going out on the car a couple times over the past few months while it was in park. Once while at a drive thru and once in my driveway. Engine stayed running both times, but all the interior and exterior lights went out. They stayed out for about 2 minutes and came back on. Both times I went on my way puzzled but no other problems.

Is it possible the overheating indication on the gauge and the lights going out are related? I don't want to have a new temp gauge put in if the real issue is some other electrical problem. Mechanic did tighten battery cables but temp gauge still spiked.

I don't have any doubts about the shop owner's honesty as he has never steered me wrong before but I need some more info to be comfortable with this. Does anyone have any ideas?

[00Beast]

Welcome!! Got any pics of your Pontiac stable?

Check your battery cables. That's the first place to start with any electrical problems. The battery is under the backseat, pull up on the front of the seat bottom and it's on the passenger side. Remove the cables, check for corrosion, and snug the bolts back up. I had the VIN run on my dad's GXP, and it had been in multiple times for battery cables and electrical issues before we bought it. When you drive it, the lights flash about 3 minutes in, every time. Not sure why.

Your mechanic is right in that the dealer's scanner, called a Tech II, can scan and cycle the gauge and see if it is properly working. His can't.

I know member *B2* on here is selling a GXP cluster, and i would bet that Morad Parts Co. would have one, or even check http://www.car-part.com. Just remember that your cluster is specific to the GXP.

[J Wikoff]

Maybe it requires a lot of work to get to on a GXP, I don't know, but coolant temp sensors are pretty cheap. No where near that $440 quote for the work. I'm trying to think of why the lights could be connected to the CTS, and I can't think of anything good. I feel pretty sure they are unrelated. The CTS's are unpowered, very simple sensors. They just have a material that changes resistance with temp.

[shoto]

Thanks guys for the replies. What a great site.

I have requests in to *B2* and Morad for an instrument cluster. Thanks again for the tip.

Mechanic did mention that the battery cable could be the problem. He said he cleaned the posts etc. and reconnected but temp gauge still reads hot. Not sure if that corrected the lights issue though.

I too suspected the CTS could be faulty and worth replacing. Part is less than $25. Although I am not sure how difficult the change-out is. I thought it would be a simple unscrew it from the thermostat housing and replace but I don't think it is there and looking around the engine I can't seem to locate the unit. Crowded in there!

Anyone know how to change out the coolant temperature sending unit?

And I'll get some photos posted ASAP.

[CMNTMXR57]

1) Checking the battery cables won't do sh*t! If they were the case, you'd have many other issues too! About the only thing it would do if anything at all, is do an idle reset (which clears all codes and errors), which is akin to re-booting your PC.

2) Coolant temp sensors are a common problem on all GM cars. They get gunked up from the Dexcool.

3) Check the actual electrical pigtail into the weatherpak connector on the coolant temp sensor. You might find that GM, in their infinite wisdom of giving their wiring harnesses absolutely zero slack for movement, may be bending it right as it comes out of the connector, causing the wire to bend and break and/or short out (if it's up against another metal object). It may also be pulling on the actual electrical contacts inside the connector. If either of these are the case, you can buy a new connector and pigtails from Caspers Electronic, and splice it into the wiring. This would definetely cause your gauge to freak out. Although more often than not, the gauge would peg at maximum from infinite resistance in the circuit. I've seen this many times. I even had to do this on my GTO!

4) GM's scan tool is a Tech2, it can do a myraid of things most other scanners cannot. But the only way it would know if the cluster was bad, would be if you (or a technician with a Tech2) did an Instrument Cluster Diagnostic check. This test through the output controls in the Tech2, asks the coolant gauge to move up and down as commanded. If it does so, then check for intermittent/loose connections (see point 3 above). If it doesn't, replace cluster.

There was a GXP cluster in the for sale section for $100 recently. You will still need a dealership, with a Tech2, and GM data center connection, to do the mileage correction on the cluster.

[CMNTMXR57]

Oh, the ECT is on the back cylinder head, driver's side.

[00Beast]

CMNTMXR, all that needs to be done for mileage is to remove the back of the cluster and swap mileage chips. No dealer trip required. I've done it myself.

[CMNTMXR57]

Yes, you can do that! You can do that on a number of other GM vehicles too! You don't think I've come across a few shortcuts in my years working on them?

Normally I'm all about shortcuts as long as the end result is the same, however, messing with mileage on a vehicle is one of the few areas where I keep my morals. Why? Doing what you did *can* be perceived as odometer fraud. Why? Because you've opened, removed, and replaced, a component that tells the PCM any mileage. In this case, that chip solely holds the mileage/trip mileage in storage, I.E. memory. When you shut off the car, that chip you swapped, simply recalls the last place it was at on your previous trip. The PCM actually does all mileage counting, adding it up on each trip, the IPC then stores it, and the process repeats. I'll get to that in a second. Now, I can't confirm this, but usually on GM vehicles, mileage is counted in two places, once in the cluster as mentioned above, and sometimes in the BCM. So as to do any comparison between the two should the need arise. However, I can't find any documentation as to such on our cars.

Any tampering like this is akin to cracking open the odometer and rolling the dials back in the old days. While at the end of the day, you've accomplished what you wanted, and ultimately you just put the correct mileage into the vehicle (not altering it to roll it back), should you sell the vehicle, and some very discerning consumer takes the car to get inspected, they pop out the cluster, dissassemble it, and notice that it looks to have been tampered with, it could open a whole pandora's box that you may not want to go down. They don't know you from Adam, so they're going to assume the worst...

Even when dealerships (GM, Chrysler, ford, honda, toyota...) do any altering of mileage whatsoever, it is documented, and in the case of GM (as I can confirm), a proper authorization/calibration ID is given. This way it IS documented. IN order to do this, it needs three things;

1) A Tech2.
2) A TIS Terminal connected to the GM Tech Center.
3) The vehicle PCM, connected to the vehicle, where it can do an SPS (Service Progamming System).

Where I do stand corrected, is that mileage isn't counted in our IPC. It is merely stored (as mentioned above), any mileage corrections need to be done through the PCM, with a Tech2, through a TIS Terminal in order to be properly authorized and documented, to save any legality issue down the road.

Sorry, not trying to be a nanny on this, but the last thing I want is something to come back to me as a fraudulent seller by simply swapping chips.

[shoto]

Here's an update on the temp gauge issue. I hope it's a tutorial for other members as well.

As noted in previous post: my mechanic believes the instrument cluster is bad but doesn't have a Tech2 to cycle the temp gauge to be positive it's bad. So yesterday I took the Bonnie to a GM dealer (temp gauge didn't go above 200 on the drive over there). Dealer cycled the gauge on their Tech2 and it checked out OK. $45

Service manager told me to bring it in the next time the gauge acts erratic. Drive it right over, don't shut off the engine, and they'll hook it up. They are giving me 30 days to reevaluate it at no additional charge.

So now I'm still in limbo; keeping my eyes glued to my temp gauge as I drive around. I can't stand just waiting for something to happen so I'm going to flush out the Dexcool, replace the CTS (coolant temp sensor) and check the wiring. Mechanic says it's 1.5 hours for him to do it but I know I can do it myself if I can just reach it.

Is the CTS located on the right side (driver side) of the back head just in front of what appears to be an engine mount? It's really hard to see down there to get a good look. I can only see what looks like a weather pak connector but can't see if it's the actual CTS it's connected to (I know, I need a shop manual). I also see 3-4 wires splitting off just before what I think is the CTS, and which are connected to a ground . Am I looking in the correct place? I hate to start moving things to get down there and not even be in the right location.

Now here's another issue regarding the instrument cluster:

I told my mechanic that I've located a used cluster. He says that I can't just buy any 2004 GXP replacement cluster based just on the make, model, year etc. of my car. He says it may not work in my car. He said I have to have the number off the back of the cluster in my vehicle. It somehow has to used to order a replacement. He said that when he orders a remanf. cluster it will come with the mileage matching the mileage on my car - no trip to the dealer required.

What don't I understand here? Why wouldn't a used cluster out of any 2004 GXP work in my Bonnie? I get the mileage issue; I can either go to a dealer to get it set to match my car's mileage and then have the proper documentation or I can swap mileage chips myself and have no documention. My choice. So, how can I buy a used cluster and be sure it will work in my vehicle (of course, assuming the used cluster isn't defective)?

Problem not completely solved yet, but hopeful - thanks guys for all your help!!

[harofreak00]

This is a mechanic that doesn't even work for GM telling you this? Your mechanic isn't God, so don't listen to him like he's preaching the Bible. We live and breathe Bonnevilles for fun, not to get paid. Who are you gonna trust?

You can use any GXP cluster in your car.

I have had at least 6 different clusters hooked up in my 00 SSEi no problem.

[shoto]

Sounds like I'm in good hands here. I know nothing trumps actual experience.

By the way, what antifreeze is a good replacement for the DexCool?

[harofreak00]

Prestone Mixes with Any.

[dpnewfie]

Why replace the Dexcool?

[lewis26]

Because it eats manifold gaskets.
http://www.dex-cool.net/

[dpnewfie]

IIRC its never been an issue in the NorthStar.

[00Beast]

Unless you don't consider the coolant crossover gaskets issues. (AFAIK, they're the same material as the 3800 LIM gaskets, and the replacements are the the same style as the Aluminum gaskets, according to other sources on this site.)

[shoto]

OK, back to the start of this thread:

It's been nice here in CA the last few days so I flushed the DexCool out and since I was messing with the cooling system I also replaced the thermostat and coolant temperature sensor. The thermostat was an easy change-out but the sensor was a bit of a pain to get at. I replaced the DexCool with the suggested Prestone. Found it at WalMart for $9.50 a gallon. Much cheaper than any of the auto stores. The thermostat and sensor were only $26. Total job was about $50. Way less than the shop would have charged.

After finally getting all the air purged I drove it around most of the day and the temp gauge is acting normal. Not sure what to think but at this point I'll just wait and see if it goes crazy.

The original thermostat and sensor were not gunked-up or corroded at all but the steel thermostat housing had a nasty black layer on the inside. It wasn't slimey but appeared to be a layer of lifted flakey black paint barely hanging on. It wiped out easily and was only on the thermostat housing (the piece that connects to the radiator hose). It was not on the inside of any of the aluminum of the water pump etc.

I don't know if the inside of the housing was originally painted and that is what is flaking off but I would not want that stuff circulating in my cooling system. It would be worth the effort to check yours. Besides, it's a good time of the year to get some fresh coolant in and get ready for the summer.

I now know where it is and how to change out the coolant temp sensor if anyone needs to know.

[J Wikoff]

Any chance of a write-up?

[Bigerik]

One thing I have heard recently is that GM used a lousy quality stepper motor on the gauges. Apparently, there are even upgraded motors available. Not that big a deal to replace them, from what I understand.

[ZimGXP]

You can also have the temp gauge rebuilt. If the car actually gets hot, you will get a message in the DIC. I'm having the same issues with mine, but when it wasn't working, the gauge would not cal. when the car was started.