Can someone help me, PLEASE???

I'm still having issues with the replacement HVAC control unit.

The unit works fine for a few hours then the temp sticks on 90 deg and "cycles" through every mode available - won't turn off.. no buttons work .. display goes almost blank - then returns. I left the fusebox cover off and can hear constant clicking as things activate/turn off.

I've checked the fuses/fuse box and ground (thanks dpd) - all fine. I've removed/replaced the 2 HVAC fuses in the interior fuse box and disconnected/reconnected the battery.

I thought I'd seen something similar in a post when I searched last week but can't seem to find it again. Has anyone had similar issues, know where a similar post is, or other ideas I can try? I'd REALLY appreciate it.


Codes:
TCS C1255 H
BCM B0432 H
RFA U1096 H

Thanks,
Lanna

 

Hello?? Is anyone out there?

 

Hi,

90 degrees is a little too hot for my liking. Can someone please provide me with some suggestions, or the link to a similar problem that someone was able to fix? I'd greatly appreciate it!

Lanna

 

Below is more detail from the Service Manual on the codes you experienced. I would swap out the HVAC controller with one from another car just to test. Would also thoroughly check all grounds. related to the HVAC circuit.

As a precaution, look under the battery. Many 97-2000's I've worked on had prior battery acid damage to the wiring harness and vacuum line inside the engine management harness. Probably not the cause of your problem, but check it anyway if you haven't.

I'd swap out the BCM (and EBTCM) if you were still having problems.

My .02.

---------------------------------

B0432 is the rear defog relay circuit. "When the BCM commands the rear defogger relay ON, the voltage level on the control circuit should be low. When the relay is OFF, the voltage level should be high. If the BCM detects a voltage level other than expected, a malfunction is present and a DTC will set."


C1255 - Malfunction with the EBTCM (Electronc Brake and Traction Control). "When DTC C1255xx is displayed on the Scan Tool, it will be followed by two more numbers which should be noted along with any other DTCs that may be displayed. The additional two numbers displayed with DTC C1255xx are for aiding engineering to determine the cause of the internal malfunction. Make sure the integrity of the connection between the EBTCM and the BPMV is secure, tight, and free from corrosion." May need to be replaced.

U1096 "This is a normal software function as long as the DTCs have a history status upon ignition cycling. No repair attempts should be made. The BCM sends out a State of Health (SOH) message to the Instrument Panel Cluster (IPC), and no SOH message response was sent back. If the problem is an intermittent loss of communications.

However, in your case, I'm not so sure.

Carefully inspect the serial data line and related components for the following intermittent conditions:
There is an intermittent open or short (to ground or voltage) in the serial data line.
Intermittent loss of communication with the IPC.
Damaged or loose star connector terminals.
If the serial data line is shorted to ground or shorted to voltage, all systems connected to the same serial data line will not be able to communicate properly. Systems capable of storing loss of communication DTCs (DTCs with the letter U as a prefix) will have these codes stored in their memory. If a DTC U1096 is stored in the BCM memory, check for the same DTC stored in the Remote Function Actuation (RFA) system. The RFA system also monitors the SOH message from the IPC. If the RFA system has a DTC U1096 stored, check the IPC for an intermittent malfunction. If the RFA system does not have a DTC U1096 stored, check for an open in the serial data line between only the BCM and the IPC. The BCM must also be checked for intermittent operation due to a loss of power or ground to the BCM itself. After repairing a DTC U1096, clear all DTCs from all systems capable of storing this DTC.
Communication DTCs do not necessarily indicate a malfunction. These DTCs are only intended to aid in diagnosing an intermittent communication malfunction that is accompanied by a symptom. If the vehicle does not experience a symptom related to a communication malfunction, these DTCs can be disregarded.
If the DTC is a history DTC, the problem may be intermittent. Perform the tests shown while moving related wiring and connectors. This can often cause the malfunction to occur.

 

Hi 78vette-sa,

Thank you for the response!

The current HVAC control unit is actually a rebuilt unit I bought a couple weeks ago to replace the original HVAC control unit that was doing the same thing. The original one had coffee spilled on it a while back which caused the buttons to stick and no longer light up. I thought that was the reason it started "freaking out" a couple weeks ago so I replaced it. The new one is doing the same thing.

I have the set of service manuals and there is some discussion about the mode actuator - do you think that could be malfunctioning? Is there any way to test it without a scanner?

The weird thing is that it works just fine for a couple hours - then freaks out. If I either remove/replace the fuses or disconnect / reconnect the battery it works fine for a couple hours... This last time I noticed that when I started the car the voltage gauge didn't drop down to 12 then rise to 14 like normal - it went to 14 then slowly dropped to 13..

I'm going to inspect/clean the main groundpoints this week. I'll check under the battery tray while I'm at it. I replaced the old battery last year because it was cracked. It didn't look like it was leaking but ??

Thank you again for your help!

Lanna

 

When you pulled the HVAC fuses (#25 I believe) you did a reset/initialize on the unit and actuators. That should have taken care of any actuator issues. If not, you should see a specific code for left or right out of whack.

I still think there is a comm issue between the BCM and HVAC systems which are interconnected. I would consider checking with someone like Gene's Karshop (forum vendor) for a used one to swap out just to make sure.

Checking and cleaning all the grounds is a good step regardless.

Good luck.

 

Hi 78vette-sa

Well, after some checking it looks like it may be related to the bcm.. so I guess I'll have to get a new one. Can I just replace it or will it need to be "programmed" for my car?

thanks,
Lanna

 

when you installed the new unit,did you start the engine and let it run for a minute or 2 to let the controller recalibrate WITHOUT touching any of the controls????????????? if not,i would take the unit out,unplug it,reinstall it and let it recalibrate.

 

Hmmm .. I don't remember.

Dang.. looks like I'll have to take the console/dash apart again Oh well, at least at this point I can probably take it apart and put it back together blindfolded.

Thank you!!

Lanna

 

I have found that wierd behavior usually indicates a problem in the power and ground circuits. If you have not already done it yet check the ground connection and connector pins for corrosion at G201, G201 and SP201 and SP202. G201 and SP201 are located at the bottom of the left A pillar. G202 and SP202 are located at the bottom of the right A pillar. Make sure you pull the connectors apart and check the pins for white or light green colored corrosion. I would also check for corrosion in the inside air temp sensor connector.

Bill

 

Hi,

Thank you so much for the advice - I'm suffering withdrawls from not driving my car... of course unless it floats, (doubtful), I won't be driving it around here for a while - good old Washington state where the only things on the roads are the rescue boats

Lanna