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Hi all,

Today went to take the GXP out and noticed the Climate Control had 3 dashed lines on the display and all of the buttons and functions are unresponsive. There is air blowing out of the defrost and floor vents (cold air thankfully). It was working perfect yesterday. I checked the HVAC fuses and those are all good. Not sure if something like this would generate any codes but I did stop at Autozone and they scanned in and of course nothing. From doing searches on the forum the 3 dashed lines means the CC module is not reading the external temp sensor? (Correct me if I'm wrong). Is my dash control unit shot?

UPDATE: O'Reilly's near me happened to have the ambient external temp sensor on hand so I tried the new one and I still have the same problem.

I assume the one you replaced is right near the hood latch mechanism?

I'll bet there is a code stored. Unfortunately, generic scanners frequently don't read proprietary codes from things like body control modules. The outside ambient temperature sensor connects directly to the Instrument Panel Module (IPM). It passes through two connectors between it and the IPM. One under the hood (C102) and one under the steering column (C201).

C102 is located in the right front corner of the engine compartment. It is inline between the main body harness and the forward lamp harness near the filler for the washer fluid. C102 has three cavities. The wire colours passing through that connector are LT GRN/BLK, YEL, BLK. You can always check to ensure the connector is intact and there is no corrosion internally at the terminals.

Does your engine temperature gauge appear to work correctly?

Yes, that is the one I replaced. I did check that C102 connector and did clean the terminals just in case. Car isn't driven in any inclement weather since 2010 and stored inside so my engine bay has remained pretty clean. Yes, the engine temp gauge appears to be normal. Drove it around the highways for about a half hour today just to see if anything would change and everything else electrical is operating normally.

I would check those fuses again with a multimeter and look for power in and out through box and fuse. visual fuse check may not be accurate - wont hurt and wont take very long.

The only fuse I can see affecting this is #33 under the rear seat. It's labeled HVAC and is 10A. Typically, with an HVAC system failure, the system is set to change the air direction to defrost. Of course if there's a catastrophic failure of some type, it may not be able to do this. The intent is that in adverse weather, this will always allow the windshield to remain clear.

The HVAC control module (control head) is obviously getting power since it displays "---". It's only source of power is from IGN-3 voltage. If that wasn't working, there would also be a crazy number of other problems with the car.

The best information will come from having the codes. Since your engine coolant temperature gauge seems to be working (I assume the needle is in the correct position at operating temp), there are not a lot of other "systems" involved that should cause this specific symptom.

This also isn't a fault I recall seeing on the forum very often, if ever from my recollection.

Took it to a shop Monday afternoon after work, and Tuesday morning they called me and said there were no faults. HVAC was operating normally and the display was normal. There were 2 codes stored, B1000 and BO159, which he said was Loss of Communication between the IPM module and the HVAC module. No kidding I drove it the 2 miles to my house and while driving it happened again...3 dashed lines and only air coming out of defrost and floor. Looks like I'm digging in the dash?

Loss of communications errors are far from uncommon with this vintage of vehicle using the Class 2 Serial Data Bus. They almost always have no effect on normal operation of the vehicle since they are typically transient. My guess is a data bus timing conflict of type resulting in one module not seeing another within the designated timeframe. Of the dozens of Class 2 based vehicles I've scanned, this has been a very common DTC. I wouldn't be chasing that at all, at least not now. The B0159 is far more concerning.

B0159 - Outside Air Temperature Circuit Range/Performance.

In my mind, this is undoubtedly the source of your grief. I would re-check the connector at the sensor and in the right front corner of the engine compartment paying extremely close attention to the terminals for any signs of corrosion. These sealed connectors sometimes do leak and can end up causing this type of fault. It definitely seems intermittent, suggestive of a poor connection or short to ground, battery positive voltage or other signal. It could also be a chaffed wire somewhere along the harness. Have there been any aftermarket additions/modifications? Sometimes with these, factory wiring is disturbed and problems develop. This can also be true of aftermarket stereos if the wiring in the dash connecting the sensor to the IPM is bad.

I would suggest replacing the sensor, but since you already have, it's unlikely two of these are faulty (especially since one was new).

I will check out the wiring again this weekend. I have an aftermarket Pioneer navigation unit that I put in way back in 2010. Following your advice, I removed the stereo and cleaned and reseated all the connections, as well as the HVAC controller itself. Unfortunately I'm still in the same boat.

Would that BO159 code be coming up if I turned the key on with the sensor removed?

Yes, that would set the code. Ultimately however, once the sensor was reconnected and the IPM detected its presence, it would become a history code instead of a current code and you would no longer see dashes on your display. A history code would not cause the display to show dashes.

Did you check the non-radio related wiring and instrument panel harness as well? It's fairly tight in there and the aluminum sub-frame of the dash has rough and/or sharp edges and protrusion in places. The IPM is in fairly close proximity to the radio bay so you may want to double check the two large, pink connectors that plug into that as well.

Finally able to get into the dash...all wiring looks good and it was pain but I was able to reseat the pink connectors as well. Prior to that, on a cold morning..about 43 F (car had sat outside) the controls were working fine and I drove it to work..about 25 miles...with no issues. Got in the car after 8 hours and it worked for about 10 minutes and hasn't come back since. I checked the voltage of the external sensor with the key on (not running) and got 5 V. Is that normal?

It ended up being the HVAC controller; bought another one off of Ebay and it works perfect! Thanks for the replies.

Glad to see you got that figured out. You can take the controller apart pretty easily and see the circuit board, it would be interesting to see if there were any bad solder connections on the board. Unfortunately, GM has had a variety of bad cold solder joints in various components over the years...the control board for the wipers that share the same component with my 98 Astro were known to fail due to this.

What is a HVAC controller?