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Discussion Starter · #1 ·
I've had nothing but blazing hot air coming out of my 2003 Trailblazer Ext. 4.2 for the past 6 months. I've gotten various responses from other forums saying to replace my complete Control Module to my Chevy Dealership finally hooking it up to their computer and it came back with OBD codes of B0414 and B0424 Air Temperature/Mode Door Actuator Malfunction.

They can't tell me exactly what that means or exactlywhat needs to be replaced.

I have the dual manual controls - one temp slider for the drivers side and one for the passenger side.

1) Do I just need to replace the 2 actuators?
2) Is it or could it be the main control module?
3) Does the whole dash need to be removed if the actuators need to be replaced?
4) Is there a special tool required? Or just a short socket?
5) If that's too much, is there any easy way to just disconnect the heat so I can drive it during the summer? (last resort. . .):cry:

They're also telling me it'll be $1000 just to remove the dash in order to get access to the actuators, etc. . .they apparently don't believe that it can be done without removing the entire dashboard!

I told them that the forums I've looked at say that you DON'T need to remove the dashboard in order to replace the actuators. Is that true? Is there a special tool?

So. . .what's my next step? Are there any other things that my need to be replaced to fix my problem other than either the Door Actuators or the complete Control Module? Any tests I can perform to confirm?

Thanks in advance ~ this problem is driving my nuts!
 

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All your questions have been answered in some very recent threads about replacing actuators, and recalibrating the system with a fuse reset trick first. Just run a search.

There's one actuator that the dealer USED to have to remove the dash. Now they have access to a special tool and a TSB telling them how to use it. Your dealer is a goof.

Read up a bit in the archived threads, then come back if you still have any questions.
 

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My step-daughter has a simular problem. When you start the TB does the heater/ac system make about 3-5-8 clicks???
 

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Discussion Starter · #4 ·
Saw the sticky, etc. . .thanks just the same. . .

First THANKS to you both for responding so quickly! :thx. . .like I said. . I've gotten quite a few responses from other forums with really no specific answers. . .

Also, I've read the sticky regarding the HVAC Actuator replacement, etc. . .and it didn't seem to exactly apply to my situation e.g. I have heat coming out exclusively from all vents. . .

I'm happy to just replace everything it could possibly be, but it would be nice to know exactly what those codes indicate needs to be replaced.

ROBERT ~ :hopeless No. . I don't get a clicking sound at all. . . and fan works normally as well (I've replaced the resistor pack before when the fan would only blow on high). No clicking sound from the actuators or doors. . .

:hail: ROADIE ~ I've reset the system, checked all HVAC fuses, etc. . .just want to know if my next step is:

a) replace both actuators, or
b) replace the main control module, or
c) could the doors (both?) be jammed with debris?
d) any other possibilities that I've left out?

I'll continue to search the threads in the mean time . . .:coffee just would love a definitive answer before I just tear in and start replacing things. . .

Oh, and YES. . my Chevy service department is very friendly and they try to help, but I don't think they're operating on the latest info :weird: . . .they actually asked me to give them the part number of the "special tool" that they'd need! I told them that "you're the one's with the shop manual. . I don't have one!". . .and I forwarded them about 5 links to the forum threads that show that you don't have to remove the entire dash to get to the actuators. . .

Thanks again so much for contributing and I REALLY hope to get this thing worked out this week! THANKS!!!!!:crazy:
 

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First THANKS to you both for responding so quickly! :thx. . .like I said. . I've gotten quite a few responses from other forums with really no specific answers. . .
There are other forums? :rolleyes:
Also, I've read the sticky regarding the HVAC Actuator replacement, etc. . .and it didn't seem to exactly apply to my situation e.g. I have heat coming out exclusively from all vents. . .
There are only four actuators. Recirculate, airflow mode, left temp and right temp. Just can you confirm that mode and recirculate work OK?
I'm happy to just replace everything it could possibly be, but it would be nice to know exactly what those codes indicate needs to be replaced.
Malfunction codes just mean that the control module can't confirm proper operation of the actuator. It might be a bad output driver in the control module, bad wiring, or bad actuators. While the dealer had it hooked up, they had the perfect chance to run the specific test you needed done, which was to COMMAND each actuator to move CW or CCW, and then read back the position sensor. That could have shown if you had a problem that was possibly not IN the actuator. But they failed to do that. They just ran a generalized test and reported that it had a fault. Sigh.....
a) replace both actuators, or
b) replace the main control module, or
c) could the doors (both?) be jammed with debris?
d) any other possibilities that I've left out?
It's not at all likely that the temp doors are clogged. One important question is: does your AC compressor really run and make your system cold, as you can tell by touching the dryer/receiver in the engine compartment on the passenger side firewall?

You could replace both actuators, being EXTREMELY careful to match the shaft position with the one you take off. Before doing that, I'd recommend just watching them reset themselves after my pull-the-fuse trick. Can you SEE them move from end to end? After 90 seconds is up, and you move the controls, can you SEE the mode actuator respond to mode commands? Does either one of the temp actuators move in response to a temp command?

Do you have any buddies to swap control modules with?

Do you have a meter and know how to use it if I explain the theory of operation of the actuators for you to monitor the harness voltages while it's recalibrating itself?
 

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Discussion Starter · #6 ·
Working on answers to your questions ~ THANKS!

Hey Roadie! First (again) THANKS so much for your awesomely quick response and detailed answer with specific questions! :hail:

1) Yes, there are other forums, but NONE so far as quick and helpful as this one has been!:woot:

2)
There are only four actuators. Recirculate, airflow mode, left temp and right temp. Just can you confirm that mode and recirculate work OK?
What is "airflow mode" . . .I imagine I can confirm that the "recirculate" works by hitting the button and seeing if the light comes on?

Also, I don't have the vehicle right now (it's still at the dealership while I continue to call them and tell them what to do next. . .pretty disappointing. . .I really just wanted a diagnostic to tell me what parts I needed to replace!) but I plan to go back and pick it up tomorrow morning at which time I'll do my best to get detailed answers to your specific questions.

Maybe I can get them to perform those tests that you recommend e.g. command CW or CCW to the actuators (I'm guessing that's Clockwise and Counter Clockwise?) and if they don't move, then the problem is not in the actuators but most likely in the control module?

It's not at all likely that the temp doors are clogged. One important question is: does your AC compressor really run and make your system cold, as you can tell by touching the dryer/receiver in the engine compartment on the passenger side firewall?
I'm not sure what the dryer/receiver looks like. . .and if I touch it, it should be cold, correct? I've hit the AC button and the light does come on, but it's tough to tell if the AC is actually running or not. . .again, once I get it back, I'll do my best to research and locate the dryer/receiver and touch it (to see if it's cold)

You could replace both actuators, being EXTREMELY careful to match the shaft position with the one you take off. Before doing that, I'd recommend just watching them reset themselves after my pull-the-fuse trick. Can you SEE them move from end to end? After 90 seconds is up, and you move the controls, can you SEE the mode actuator respond to mode commands? Does either one of the temp actuators move in response to a temp command?
Not exactly sure what the "pull-the-fuse trick" is. . .also havn't disassembled enough yet to actually see the door actuators move yet. . .and again, don't know what the "mode actuator" is. As far as temp commands. . .I think you mean when I move the temp controls from hot to cold or vice versa. . .and NO, there is no response on either side, meaning the air continues to blow HOT. .not sure if the actuators move or not cause I can't see them yet. . .just hot air blows from all vents. . .dash vents and feet vents. . .AC has no effect.

I don't have any friends :sadcry: cause I'm too busy trying to fix my heat issue! So, I can't swap out the control module, however, I found some on Ebay for around $90 used at http://cgi.ebay.com/ebaymotors/ws/e...0327605403&sspagename=STRK:MEWAX:IT&viewitem= It looks like mine. . .ought to work, right?

Do you have a meter and know how to use it if I explain the theory of operation of the actuators for you to monitor the harness voltages while it's recalibrating itself?
I DO have a little digital Radio Shack Voltmeter :yes:. . .I can check AC and DC voltage, resistance, continuity, etc. . .not a professional, but I think I can get by. . .checking to see if there's juice going to the actuators and how much juice shouldn't be too much of an issue. . .

Again, I'll get more detailed answers to your questions as soon as I get my vehicle back ~ :hail: THANKS SO MUCH for your detailed reply and help with this problem!!!!! :thx
 

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What is "airflow mode" . . .I imagine I can confirm that the "recirculate" works by hitting the button and seeing if the light comes on?
Airflow mode is the choice of output vents. Floor - Dash - Windshield. Those are the modes. One actuator moves a door to guide the airflow to those three (plus combinations) zones. Never trust a mere light on the control module. It just tells you what was requested, not what the actuators actually did accomplish.
Maybe I can get them to perform those tests that you recommend e.g. command CW or CCW to the actuators (I'm guessing that's Clockwise and Counter Clockwise?) and if they don't move, then the problem is not in the actuators but most likely in the control module?
Not for sure. Let's say you have a remote for your TV. You hit the buttons and nothing changes on the TV. Do you have enough information to conclude the fault is definitely with one OR the other? Statistically, you might conclude it more LIKELY to be dead batteries in the remote, but it might be a failure of the TV, or somebody put a piece of gum over the end of the remote and its signal isn't getting TO the TV. See the issues? You need another tool to look at those invisible signals, or another remote, or another TV, to get a third opinion.
I'm not sure what the dryer/receiver looks like. . .and if I touch it, it should be cold, correct? I've hit the AC button and the light does come on, but it's tough to tell if the AC is actually running or not. . .again, once I get it back, I'll do my best to research and locate the dryer/receiver and touch it (to see if it's cold)
It's the aluminum octagonal thing on the left of this pic.



Not exactly sure what the "pull-the-fuse trick" is. . .also havn't disassembled enough yet to actually see the door actuators move yet. . .and again, don't know what the "mode actuator" is.
The fuse trick is the way to reset the control module and force it into its recalibration process. When you read one of the right archived threads, you'll know it.

There are three actuators on the driver's side of the HVAC plenum unit under the dash, one on the right center, and one far to the right near the blower (I misspoke before about there being 4). The far right is recirculate. The one on the right center is passenger temp. The lowest one on the driver's side is driver's temp. Middle one is mode (floor/dash choice) and the upper one is windshield vent mode.

Start getting used to seeing this drawing. I think I'm about to turn this into an all-purpose tutorial.





As far as temp commands. . .I think you mean when I move the temp controls from hot to cold or vice versa. . .and NO, there is no response on either side, meaning the air continues to blow HOT. .not sure if the actuators move or not cause I can't see them yet. . .just hot air blows from all vents. . .dash vents and feet vents. . .AC has no effect.
OK. You'll get the dash panels off soon enough. I took mine totally apart to put in an offroad grab handle, but you won't have to go this deep. I may use pics from my project to show where the actuators are though:


I don't have any friends :sadcry:
...unfortunately, that's a problem beyond trailvoy's ability to solve. :laugh:
cause I'm too busy trying to fix my heat issue! So, I can't swap out the control module, however, I found some on Ebay for around $90 used at http://cgi.ebay.com/ebaymotors/ws/e...0327605403&sspagename=STRK:MEWAX:IT&viewitem= It looks like mine. . .ought to work, right?
There are no year-to-year changes in the module, so the cheaper the better.
I DO have a little digital Radio Shack Voltmeter :yes:. . .I can check AC and DC voltage, resistance, continuity, etc. . .not a professional, but I think I can get by. . .checking to see if there's juice going to the actuators and how much juice shouldn't be too much of an issue. . .
Great.
 

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My code scanner library reports the B0414 is the "Temperature Control #1(Main/Front) Feedback Circuit Range/Performance" and the B0424 as "Temperature Control #2(Passenger) Feedback Circuit Range/Performance"

Hope this helps some.
 

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Hope this helps some.
Warning - tech talk: The actuators have a failure mode where the motor can rotate past where its supposed to stop. To save money on the design, the feedback circuit (actually a potentiometer like a volume control) is attached to the motor side of the final gear. That final gear is pressed onto a knurled shaft and it may not be pressed down fully on the shaft.

The end result is that the knurled shaft might slip on the final gear, and that can send the potentiometer BEYOND its end point, and then its reported resistance goes beyond its highest value, and starts again at zero. The control module calibration algorithm expects the resistance to always increase (monotonically) with CW rotation (it might be CCW, but that isn't critical).

When the feedback pot resistance goes to zero and then starts increasing again, the control module freaks out (non-technical speak for "the algorithm fails to converge to a solution") and it gives up. A couple of us have repaired failed actuators by disassembling them, analyzing where the knurled shaft SHOULD be on the gear, and then pressing it back together tighter. Saving a few $$ on the actuator. This is not for the average mechanic unless you know electrical systems too.

The good news is that if you have a meter, and just monitor the feedback circuit voltage, it's easy to tell if this is happening.

 

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Discussion Starter · #11 ·
New Info & Pictures

Hey Roadie!

Picked up my TBlazer today from that useless Chevy Dealer :raspberry and couldn't wait to jump in & work on it and get you some answers to your questions to help me get this thing fixed! :thumbsup:

Here's what I've been able to determine so far:

There are only four actuators. Recirculate, airflow mode, left temp and right temp. Just can you confirm that mode and recirculate work OK?
The "Airflow Mode" actuator is working perfectly ~ I was able to watch the actuator turn as I moved the airflow mode switch. The "Recirculate" actuator "seems" to be working ( I hear the difference in "air sound" as usual, but I don't have access to that high in dash on the passenger side as of yet.

I noted the position of the Actuator "spindle", pulled off the 2 screws and gently removed it and unplugged the harness. I then put a piece of Masking Tape by the doors "handle" to indicate the original position it was in, then I turned it Counter Clockwise about 60 degrees and the Heat went off! (on the drivers side, that is. . ) Pretty COOL!



Just for the heck of it, I pulled the actuator apart to see if there were any obvious signs of something wrong. . .gears all look like they have their teeth, no broken parts inside, etc. . .for anyone that cares, here's what it looks like inside:



One important question is: does your AC compressor really run and make your system cold, as you can tell by touching the dryer/receiver in the engine compartment on the passenger side firewall?
The dryer/receiver started off warm, then I hit the AC button and waited about 5 minutes. . .it cooled off a bit, but not too much. . .Compared to my 08 Avalanche ( i did the test on the Avalanche as a comparison) it didn't cool off nearly as much . . .

Do you have a meter and know how to use it if I explain the theory of operation of the actuators for you to monitor the harness voltages while it's recalibrating itself?
I do have my ESV and NOW I also have access to the Harness going to the actuator to check voltages! There are 5 wires going to the harness. .. pictured here:


LtBlue w/blk stripe
LtBlue
Yellow
DrkBlue
Brown

What should the voltages be under what conditions?

I went ahead and ordered the Drivers Side & Passenger Side Actuators today. . won't be here for at least 3 or 4 days. . can I check the voltages in the mean time?

Anything else I can check or should I just chill out and wait until the actuators get here and install them and see if that fixes the problem? They said once they're installed, I can't return 'em so I'd kind of like to confirm that the actuators are the problem. . .

Also, how much of the passenger side to I need to disassemble in order to get the the Temperature Actuator on that side?

:hail: Once again, thanks in advance for all of your help, let me know if you'd like me to take any more pictures while I have it apart for anyone elses reference, thanks, thanks, thanks and look forward to hearing back! :thx
 

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Just for the heck of it, I pulled the actuator apart to see if there were any obvious signs of something wrong. . .gears all look like they have their teeth, no broken parts inside, etc. .
Great work! And thanks for the pic. I failed to do the same when I was inside mine. Anyway, the slippage point was between the metal and plastic at this point.



The problem with fixing this actuator is that the blue gear is the feedback position potentiometer. Once the final gear spins on its knurled part, the relationship is ruined, and you have to rediscover the relative positions of the knurled metal output socket and the potentiometer. If you're off by a tooth or two, the recalibration algorithms fail and the control module just gives up on that actuator.
The dryer/receiver started off warm, then I hit the AC button and waited about 5 minutes. . .it cooled off a bit, but not too much. . .Compared to my 08 Avalanche ( i did the test on the Avalanche as a comparison) it didn't cool off nearly as much . . .
Ick. Bad. You should get it to an AC pro to check the pressures.
LtBlue w/blk stripe
LtBlue
Yellow
DrkBlue
Brown

What should the voltages be under what conditions?
I've never fiddled with the passenger side actuator, but taking pictures of any of them while the dash panels are off would be helpful for the archives.

Anyway - theory of operation:

Pin 5 - Brown is 12V from the ignition switch RUN bus, fused by fuse #39 in the rear.

Pin 6 - Dk Blue (Dk Green for me) is the position feedback signal.

Pin 7 - Yellow is a zero volt reference from the module

Pin 9 - Lt Blue (purple for me in 2004) is the control signal

Pin 10 - Light blue/black stripe is a 5.0 V reference from the HVAC control module


12V, 5V and zero are all constant voltages.

The control signal has only three states. 2.5V commands no movement. Zero volts goes one way (don't know if it's CW or CCW). 5V goes the other way. During recalibration, the control module spins each actuator to the stops, CW and CCW, to discover when the motor stalls out and what the position feedback sensor is reading just as it stalls out and quits moving. Then it remembers this value and makes sure it doesn't hit those stops in future operation because it's potentially damaging to the actuator. If the flap door stops the final output socket (the metal hub in the final gear) but the motor is able to continue to move the gear and it rotates on the knurled part, that's the root cause of many failures.

So pull fuse #36 in the rear to get the control module to lose its memory, and force the recalibration, and you should be able to see Pin 9 cycle among 0, 2.5 and 5V.

The position feedback signal is just the wiper on a potentiometer with 5V reference on one end and zero volts on the other end. So the signal can vary continuously from 0-5V, except the mechanical stops will usually hold it to a narrower range. Never as low as zero and never as high as 5. And if there hasn't been any knurled strippage along the way, it will be a smooth curve, always increasing or decreasing slowly. If the pot is misindexed compared to the final gear, the problem comes when it starts off at 3V, let's say, instead of zero. So when it increases, it goes PAST 5V, and jumps immediately to zero, then increases smoothly to 2V, as the pot wiper spins all the way around. This discontinuity from 5->0V is what confuses the calibration software, and it just gives up.

 

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Anyway - theory of operation:

Pin 5 - Brown is 12V from the ignition switch RUN bus, fused by fuse #39 in the rear.

Pin 6 - Dk Blue (Dk Green for me) is the position feedback signal.

Pin 7 - Yellow is a zero volt reference from the module

Pin 9 - Lt Blue (purple for me in 2004) is the control signal

Pin 10 - Light blue/black stripe is a 5.0 V reference from the HVAC control module
Excelent info. I wanted to point out, however, that the pinout descriptions for Pin 6 and Pin 9 in post #12 are swapped. Pin 6 is actually the control signal and Pin 9 is the position feedback signal...
 
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