Temp gauges flat lined
 

I purchased a 2006 4 months ago with 55K miles on it. When I was driving at highway speeds the other day, the check engine light came on and the temp gauge flat lined to zero. I/P diagnostics for engine temp showed 3 flat lines before the F for temperature. When I took it to the local dealer they said it needed a thermostat installed, of which they were more than happy to put one in "after they ordered the 'kit' for $90, and the cost installed would be $390". I told him politely to forget that thought and I would call the selling dealer to see if they would do anything (of which they were quick to say 'the warranty had expired' [3 months/3000 miles]). the next day at the same speeds, it began working as normal. It since has quit twice now and the gauges all go back to normal working condition. I'm a shade-tree mechanic from the 70's and this seems somewhat ridiculous to me. If the temp sending unit would go out, it would stay out wouldn't it? If the thermostat took a s---, wouldn't it stay in that condition as well? Has any other members had this happen?
signed,
Punkin Head-ache

Welcome, sorry that mechanical issue brought you here. But it sounds like your thermostat is stuck open. Check out this post: https://www.chevyhhr.net/forums/problems-service-repairs-42/check-engine-light-came-after-coolant-guage-stop-working-8188/

Looks like you just joined the forum, Welcome. Being a shade tree mechanic from the 60's, a Thermostat could unstick since the coolant is constantly changing from hot to cold or cold to hot but usually they will hang open.

Mine did just that after this happened to me.

After 2 or 3 days everything went back to normal. I do keep a close eye on things though.

Do you get a "normal" amount of heat from your heater when the gauges die ? If you do it is not likely to be your thermostat. Most likely electrical. You could check this with an infared thermometer. Radio Shack or Harbor Frieght. Check engine temp when gauges work and when they die. If temp is the same, not a thermo. problem.

Did first dealer check for "codes"? check eng. light should set codes.
I would stay away from ANY shop that "shots from the hip" and guesses a cause.

Good Luck.

Thank you all for the information and the welcome to the sight. I really don't want to donate nearly $400 to fix a damn thermostat, but I guess that's why we can't work on the cars anymore and they truly do get the 'big bucks'. I will pursue the thermostat change since the temps fell to 30 overnight and the the car barely got warm (showing another flat lined temp gauge). I have to believe the 'stat is locked open (thank God, I smoked a block with one locked closed before, not pretty). I look forward to continued communication with the members of this site, very helpful and informative! BTW - that's a "shade tree mechanic from the 70's" there an08HHR, I was born in 1960 and the ol' man wouldn't let me touch a wrench until I was 10, so I could work on my first car.

[QUOTE= BTW - that's a "shade tree mechanic from the 70's" there an08HHR, I was born in 1960 and the ol' man wouldn't let me touch a wrench until I was 10, so I could work on my first car.[/QUOTE]

I was referring to me when I said 'as shade tree mechanic in the 60's'. Iwas born in the mid 40's

IF you do not go to a dealer the them replacement will be far less, I despise dealer service and look forward to the expiration of the 36/36 warranty.

Sorry an08HHR, I misread the statement. Thank you for your input though.

:thumb:

Mine just did this again, be going in to the dealer this week.

Well, they replaced the thermostat. Hope this does it.

Strange thing is, let me know if this is normal, I've been smelling something like when I had cars in the past overheat. Could this be the result of a sloppy job pouring and the excess is now burnming off?

I know this has been said to be a myth, but have you guys checked to ensure all the relays are pushed in all the way. I didn't have any issues but I did have a couple relays move alot when I checked mine for the first time at about 30,000mi. Just a thought. I really don't think it could be a thermostat, did either of you notice how quickly or slowly the gauge dropped? If it just slowly fell to the bottom it might be the thermostat, but if it just fell like when the car turns off then it has to be electrical.

Ive been lurking around here for some time, sorry for the lack of an introduction post. I'm not a 'real mechanic' but having spent two years in college for an AAS degree (in cars) I believe I know what you're issue is, and your guess was pretty good as well. If it flatlines to zero degrees your issue would not be your thermostat. You can remove your thermostat from the vehicle and will still get a reading above zero.

Zero degrees is (or was on the older gm cars) recognized by the PCM as a zero volt reading. Check the wiring or replace the temp sensing unit. It should be in the block somewhere reading the temp of the coolant. Chances are you'll have to lower the coolant level.

And it will fire off a trouble code as a zero volt reading is read by the engine as -40 degrees (or -70, i cannot remember) but the car compares that reading with the rest of the readings (intake air temp for one) and can determine which sensor is giving the bad readings. I would think that once it goes out its out for good so maybe the wiring is lose, or there is dirt in the connection somewhere. Check that out if you have a voltmeter you'll be in good shape.

Hope this helps.

**Off topic** I do plan on actually posting more and buying a HHR... hopefully a Victory Red SS will be in my driveway next year.

Cheers!

Welcome Shefz28. Anyways, good to receive info and the more we get the more we can help one another with problems, and where to get items also. Since you have been lurking for some time, that much mean you like the site.

ShefZ28....

First welcome to this forum. Your involvement will always be appreciated.:thumb:

Your diagnosis is also in my way of thinking. I have operated vehicles with thermostats removed, and always had SOME indication (movement), of a temperature reading, on an analog gauge. So I am in belief the thermostat is NOT the problem. Still sounds more on the electrical side to me.

For those who have had the analog display zero out, did you check the DIC reading at that time??? Or did "everything" go out??

I don't disagree with what you guys are saying.

All I know is I took it in and that's what they fixed. At least now it's on record as having the problem. didn't cost me anything but some time. if it happens again, I'll go back. If not, even better.

One thing that us "old farts" need to keep in mind is that modern cars don't just have a sending unit connected directly to a gage anymore. The signal goes through the computer now.

The Diagnostic Trouble Code (DTC) for a stuck open thermostat is P0128 for "Engine Coolant Temperature (ECT) Below Thermostat Regulating Temperature". Many auto parts stores will pull codes at no charge (Autozone does it in my area).

A friend and member here just went through this on his HHR. No readings, MIL. The dealer messed up the first visit and reflashed the ECM per a TSB and code update for sensitivity range, but that pertained to the 2.2, not the 2.4, which his was. The second trip, the thermostat was replaced and all is fine now.

I'm in agreement with you Joe.

But I think someone, I believe oneton, mentioned the HHR has 2 sending units. That has me wondering, and why I asked the question, of the possibility of the DIC temperature working correctly at the time the analog gauge is "bottomed out". I would think if that indicator is displaying the normal temperatures usually experienced, the thermostat is not at fault (but, it could be blanked .....- - -... out, as well).

Now, I do admit that I have no idea what the 2 different temp. sensors are for. I'm just trying to use some rationale (effective or not) and try to help resolve somebodys problem.

Wow, I'm thoroughly impressed with the knowledge that abounds these pages! And yes, both gages do go immediately to flatline and the car is heating normally, (saying that from 30 degree mornings here). Mine is still in and out of registering a temperature and the check engine light seems to accompany those spasms. I just can't bring myself to dump nearly 400 clams into the dealer for something so trivial. Where are the 2 sending units mentioned in here? I can assume 1 is block-side, but the other seems like a waste, but that's what keeps us "old farts" from working on the damn things! So for you guys that had the thermostat replaced, is that truely what was done or did the dealer merely check/fix loose relays and send you on your way. Or did they soak you for replacement costs (if out of warranty) and do the relay thing as well? Can't help but wonder............

Analog Temp Gage Flat and engie coolant reading ---F
 

Hi all
I seem to have a similar problem. This happened 2x's in the last 20000 miles.
Driving along at highway speeds and I look down to check the gages and I fing the analog temp gage (likely running through the computer) falls flat - no reading what-so-ever.

Since it was warm out, I was using the AC. I also noticing it was blowing warm air.

Later that evening, while driving home I noticed the analog temp gage working and the temp read 189F. The AC also worked... hmmm...

What's more interesting is: no service or engine lights.

Sounds like an electrical issue to me? Any ideas? Temp sending unit?

Thanks!
Warren

Most people have had the issue traced to a faulty thermostat. Mine did the same as you are describibg and that's what the fix was.

Just ran in to same problem just like to know if there is a thermostat that are made the same as the gm one with out the rubber that cause the problem.. Like any other brand that cost less .. Thanks

The GM part is "competitively" priced.

GM part is only expensive at the dealership not so much online
ZZP for instance has them for $14.99

Thanks old blue .. I seen go for like 34$ just crazy for a stat.. What is the link for zzp thanksACDelco 12T103D Professional 180 Degrees Engine Coolant Thermostat with Gasket is this the one?

Stants go for $30ish.

Yup that's it $14.99

Pumpkin head as a shade tree Mechanic no reason on an HHR that you can't change out the thermostat in 30 minutes.

Pick one up at a local supply or dealer and get r done :)

At least that way you are out less than $30.00 buck and you know you have a good T-Stat in there. then if this continues chase down a sensor or bad connection.

Just an FYI I recently had the interior lights start turning on by themselves with all doors closed!!! Checked all the door switches etc, and nada, as someone mentioned previously, open that fuse/relay box under the hood and reseat every dang relay, fuse etc in there. After doing that I had no further problems.
And 90% of them moved! as in they were not fully seated.

Ahhh, Punkin Heads post was from 2007 - 8 years ago.

Same thing happened to my 1LT last fall. I picked up a new thermostat from NAPA, some new coolant (50/50 dexcool), followed this post below, and had it changed in my driveway in under an hour.

https://www.chevyhhr.net/forums/how-tutorial-library-21/how-save-$350-00-thermostat-replacement-2-4l-p0128-24493/

FYI my LT is a 2.2 and could follow the instructions just fine.