Temperature gauge and A/C stop working

Are those the only items that have a problem? Lights do not dim or the engine stutters, even something minor? Anything that seems to make it happen, like hitting a bump, driving slow/fast, turns?
When you say the AC stops blowing cold, do you mean the blower speed stays the same but the cold air starts to warm up or does it go from cold to hot like you were turning the heater on?

The temperature gauge dropping should not matter to the AC system as it only cares that the coolant temperature is below 253 degrees. However it could be a symptom of the problem.

As you can disconnect the battery and it suddenly resets I suspect there is a code being stored in the HVAC module that is pointing at what is shutting the system down. Those codes can be read using a dealer/good shop scan tool.

Hello,

This problem has been traced back to a faulty cluster. The cluster must be replaced or updated to fix.

Even though this fix is straight from the dealer, I think it might be a gauge stepper motor problem.

Please use 2CarPros anytime, we are here to help and tell a friend.

I had this problem for over a year on my wife’s 2008 Envoy. Sensor ohms tested fine. Plug was fine zero corrosion. Handed the Envoy off to my new driving daughter and was fixing to buy a new ECM for a shot in the dark. Luckily the truck didn’t start dead battery... low and be hold the battery cables were loose. Battery was bad after a good charge. New battery tight cables and haven’t had the issue for over 2 months now. Hope this helps someone. If your battery cables are tight at the battery check the positive at the starter and your ground where it is connected.

I just recently bought the vehicle listed above from a family friend. Everything was working fine until about 4-5 days ago. I left my house in the morning and shortly after leaving the A/C stopped working. Then I noticed that the check gauge light had came on also and the temperature gauge was not working at all, staying all the way down. It has remained this way. It does not fluctuate. It is like this as soon as I start the vehicle every time.

Good afternoon,

Sounds like the coolant temperature sensor has failed.

I attached the location for you of the sensor.

Roy

Engine Coolant Temperature Sensor Replacement

Removal Procedure

Notice: Use care when handling the coolant sensor. Damage to the coolant sensor will affect the operation of the fuel control system.

1. Turn the engine OFF.

Caution: Refer to Battery Disconnect Caution.

2. Disconnect the negative battery terminal.
3. Drain coolant below the level of the engine coolant temperature (ECT) sensor. Refer to Cooling System Draining and Filling (LL8) Cooling System Draining and Filling (LH6, LS2).
4. Disconnect the ECT sensor electrical connector (1).

My question is to Ken the Administrator. In a previous blog about 2008 Trailblazer with a temperature gauge intermittently not working and setting code 128, you stated that it traces back to the BCM. Could you kindly explain how the BCM controls this? Could you also tell me the BCM's location and does a new one need to be reprogrammed by the dealer? My 2008 Trailblazer just developed this problem.

I have never seen a P0128 to be caused by a temperature gauge problem. That codes means that the engine is not reaching sufficient temperate to satisfy what the computer has been programmed to look for.

Yes that is what P0128 means but that does not mean that is the problem. My problem is not a temperature problem. My gauge intermittently goes out like when the ignition is off thus setting the code. in another blog feed here by Ken "Admin" mentioned it traces back to the BCM which obviously controls the gauge and possibly the signal from either the temperature sensor or gauge or both to the PCM. When the signal is interrupted to the PCM it sets the code.

The Body Control Module plays no part in the temperature gauge circuit on this vehicle.

What you need to do is monitor the ECT reading with a scan tool and compare it to the dash reading at the moment this is happening.

Thanks. You are suggesting it is the ECT? Others have replaced the ECT and thermostat and still have the problem. Could a bad stepper motor set the code?

I suggested to compare the dash reading with the data reading in the PCM to see if they match when the problem occurs to help isolate the cause.

Hi,

I must have been mix up on that one I updated the post. They make stepper motors you can buy on Amazon.

https://www.2carpros.com/questions/2008-chevrolet-trailblazer-2008-chevy-trailblazer-coolant-temperature-gauge

Check out.

https://www.amazon.com/gp/product/B01B782Q14/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=2carprcom-20&creative=9325&linkCode=as2&creativeASIN=B01B782Q14&linkId=9dfca5114e8bc433181ee5a8bb28c134

Sorry about that. :)

Please let me know.

Cheers, Ken

Thanks Ken, This should solve my problem.

If in fact you have a gauge issue within the cluster, I do not believe it will set a P0128 code. The PCM sets that using data from the CTS.

Thanks Wrenchtech. So far it seems to be leading toward the stepper motor. I will double check the CTS. The problem is intermittent and I might just change it anyway. If the problem persists then I will rebuild the gauge vluster.

I am not saying the CTS is the problem. It could just as easily be a wiring problem in the circuit or the motor just not getting hot enough. That is what comparing the scan tool data could tell you.This could be as simple as the plug at the CTS being bad.

my engine temperature gauge is not working propaly and the dash board give the there is some malfunction error now it's give a check engine sign what shall I do

P.S: My AC also stopped cooling

If the check engine light is on, have the computer scanned to identify trouble codes.

Here is a guide to help.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down this guide and report back

Cheers

Air conditioning and engine cooling liquid temperature gauge is not working I checked fuses for the air conditioner and found them to be in order

There is no fuse for the temperature gauge. the sender unit may be bad. it is by the thermostat housing. have it checked to verify.

Roy

Engine Cooling problem V8 Two Wheel Drive Automatic 49000 miles

Twice coolant temperature gauge has failed to register pass 100F. After approximately 10 minutes driving time, gauge warning light came on and AC quit working. Engine is not overheating. Dealer replaced thermostat after first occurrence. Problem came back few weeks later but self corrected - gauge started working, warning light went out and AC came back on. Gauge readings are erratic at times - between 165 and 210 ( 1/4 mark to 1/2 mark on scale ). Gauge never reads past 220. I have Chevrolet TrailBlazer LS 2008 ( American Version ) having 65000 miles

I am facing problem of dropping of temperature gauge while driving. It comes automatically down after some time during driving. One of the mechanic has replaced temperature sensor but problem still persists. Moreover, once temperature needle goes down to zero during driving, Air conditioning COOLING system also stops working during that period. Sometimes temperature needle works perfectly fine and sometimes drops automatically during driving. Once mechanic RESET from computer, it becomes ok but again same thing happens after few days. I am really so worried. Please help me to resolve this issue.

the dealer have change the coolant temperature sensor, water pump and also the dealer try to fix wires lose but it does not fix the problem. Could it be because of the battery?

Intermittent temp gauge and of course the AC stop by default when that happens. So, What's the big secret? This thread is listed under. This thread started 6 years ago and there is no answer to this VERY COMMON problem?

Not just here but threads all over the internet with no answer. You can leave off the list Temp sensor / Thermostat / Wiring. It's none of these. LoL!

Hal

Any ideas on problem???

Hello,

This problem has been traced back to a faulty cluster. The cluster must be replaced or updated to fix.

Even though this fix is straight from the dealer, I think it might be a gauge stepper motor problem.

Please use 2CarPros anytime, we are here to help and tell a friend.

Best, Ken

My question is for Ken the Admin. How does the BCM affect the temp gauge? My '08 trailblazer just developed this problem. I cleared the code 128 and the gauge is working fine for now. I expect it to be intermittent.

Today my service engine soon light came on and my engine coolant temperature gauge dropped below normal range. Then it would start fluctuating back up to near normal than back down. Can you please help me? Thank you

since engine light is on you need to have trouble codes pulled, most local auto part stores do this for free. most likely engine coolant temp. sensor has failed but could be other things, trouble code(s) should point out the issue.

Hi there,

First thing to do is get a scan done to check for any unresolved fault codes, the check light is indicating that a code has been set, do this and report any codes here for further assistance.

mark (mhpautos)

im just a shade tree mechanic my gut sais thermostat needs replacing but might as well change temp. sensor also thermostat behind alternator comes as housing my check engine lite was engine not reaching proper temp when i turned on the heater it went to 210 and lite went off so im changing thermostat and antifreeze its usally a good idea to change about every 5 years my experiance.