HVAC Control Module (K33) PWM voltage levels

Shingadaddy · July 26

Hi and thanks to and for the forum. 2017 GMC Sierra crew cab 4wd 5.3 SLT. Blower quit. AC compressor not engaging. Blower inspected and has RUST and bad corrosion on PCB.

Maybe moisture or a cap blew and spew. Not sure but pull up voltage on Blower PCB that is usually on the PWM line is not present causing inhibited AC clutch and of course blower does not run. Replaced blower with 4 Season 75039. AC clutch works now and pull up voltage on PWM line from K33 to motor now present but only 2 volts. I can see Varying PWM but it is only 2volts peak. Motor does not run consistent and starts and stops intermittently. Got a second blower motor and same thing. I am scoping the power, ground and the PWM signal RIGHT AT THE MOTOR. Voltage for power 11.98, engine off. A little puzzled and was wondering if anyone had info on how high the PWM line should be?? I also can ground the PWM line (Like the K33 does) and i figure the motor would run on high.Nope.... Motor does not run. Any help would be appreciated.

Thanks!

Edited July 26 by Shingadaddy

Shingadaddy · July 27

I see views piling up by my post has a star instead of a dot and looks pale, almost greyed out. And 0 replies????

Was this question not allowed or what am I doing wrong??

mikeyk101 · July 27

2 hours ago, Shingadaddy said:

I see views piling up by my post has a star instead of a dot and looks pale, almost greyed out. And 0 replies????

When a star appears there, it means you participated in a thread. And if it's grayed out, it means nothing new has been added to the post. If a dot or star is blue, it means there is a new post and if you click on the blue star or dot, it takes you directly to the newest post.

Unfortunately, there have been several members that have viewed the topic but the question is probably above the ability to understand and/or diagnose your issue of most members and that explains the lack of responses.

newdude · July 27

On 7/25/2024 at 11:07 PM, Shingadaddy said:

Hi and thanks to and for the forum. 2017 GMC Sierra crew cab 4wd 5.3 SLT. Blower quit. AC compressor not engaging. Blower inspected and has RUST and bad corrosion on PCB.

Maybe moisture or a cap blew and spew. Not sure but pull up voltage on Blower PCB that is usually on the PWM line is not present causing inhibited AC clutch and of course blower does not run. Replaced blower with 4 Season 75039. AC clutch works now and pull up voltage on PWM line from K33 to motor now present but only 2 volts. I can see Varying PWM but it is only 2volts peak. Motor does not run consistent and starts and stops intermittently. Got a second blower motor and same thing. I am scoping the power, ground and the PWM signal RIGHT AT THE MOTOR. Voltage for power 11.98, engine off. A little puzzled and was wondering if anyone had info on how high the PWM line should be?? I also can ground the PWM line (Like the K33 does) and i figure the motor would run on high.Nope.... Motor does not run. Any help would be appreciated.

Thanks!

Did you scan for codes prior to diagnosing? HVAC system can set multiple codes, one of them being B0193 Front Blower Motor Speed Circuit.

The K33 HVAC Control Module is located on the blower box itself, behind the passenger side of the instrument panel, at the top of the HVAC box. In the catalog its referred to as the Heater and AC Remote Control Module.

DTC B0193

DTC Descriptors

DTC B0193: Front Blower Motor Speed Circuit

For symptom byte information, refer to Symptom Byte List.

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
B+	B0193 06	B0193 06	—	—
Control	B0193 06	B0193 06	B0193 01	1
Ground	—	1	—	—
1. Blower Malfunction

Circuit/System Description: The blower motor speed control signal from the HVAC control module, battery positive and ground circuits enable the blower motor to operate. The blower motor control circuitry is integrated within the blower motor assembly. The HVAC control module provides a ground pulse width modulation (PWM) signal to the blower motor to request a specific motor speed. The blower motor translates the PWM signal and drives the motor accordingly.

Conditions for Running the DTC

Ignition ON.
The HVAC control module is ON.

Conditions for Setting the DTC

B0193 01

The voltage at the HVAC control module output to the blower motor control module is always high.

B0193 06

The voltage at the HVAC control module output to the blower motor control module is always low or fluctuating.

Action Taken When the DTC Sets: The blower motor is inoperative.

Conditions for Clearing the DTC: The condition for setting the DTC is no longer present.

Diagnostic Aids

The design of this motor does not allow for bench testing. The motor will not operate by simply applying power and ground.

Inspect the motor shaft for rust or other foreign material which may prohibit proper motor operation.

Check for Preliminary Information or Technical Service Bulletins. Circuit/System Testing

Note: Verify the ignition is OFF before connecting the blower motor or incorrect test results may occur.

Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the M8 Blower Motor. It may take up to 10 min for all vehicle systems to power down.
Test for less than 10 Ω between the ground circuit terminal 6 and ground.
- If 10 Ω or greater
1. Ignition OFF.
2. Test for less than 2 Ω in the ground circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, repair the open/high resistance in the ground connection.
- If less than 10 Ω
Verify a test lamp illuminates between the B+ circuit terminal 1 and ground.
- If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF, remove the test lamp.
2. Test for less than 2 Ω in the B+ circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse.
- If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF, remove the test lamp.
2. Test for infinite resistance between the B+ circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - If infinite resistance, replace the M8 Blower Motor.
- If the test lamp illuminates
Remove the test lamp.
Ignition ON. Test for less than 1 V between the control circuit terminal 2 and ground.
- If 1 V or greater
1. Ignition OFF, disconnect the X2 harness connector at the K33 HVAC Control Module. Ignition ON.
2. Test for less than 1 V between the control circuit and ground.
  - If 1 V or greater, repair the short to voltage on the circuit.
  - If less than 1 V, replace the K33 HVAC Control Module
- If less than 1 V
Ignition OFF. It may take up to 10 min for all vehicle systems to power down.
Test for infinite resistance between the control circuit terminal 2 and ground.
- If less than infinite resistance
1. Disconnect the X2 harness connector at the K33 HVAC Control Module.
2. Test for infinite resistance between the control circuit and ground.
  - If less than infinite resistance, repair the short to ground on the circuit.
  - If infinite resistance, replace the K33 HVAC Control Module
- If infinite resistance
Ignition OFF, connect the harness connector at the M8 Blower Motor. Ignition ON.
While backprobing terminal 2 at the M8 Blower Motor, test for greater than 1 V between control circuit and ground.
- If less than 1 V
  Replace the M8 Blower Motor.
- If 1 V or greater
Verify the voltage decreases and increases while using the controls to change the blower speed selection.
- If the voltage does not decrease and increase as the blower speed selection is changed
1. Ignition OFF, disconnect the X2 harness connector at the K33 HVAC Control Module.
2. Test for less than 2 Ω in the control circuit end to end.
  - If 2 Ω or greater, repair the open/high resistance in the circuit.
  - If less than 2 Ω, replace the K33 HVAC Control Module.
- If the voltage decreases and increases as the blower speed selection is changed
Replace the M8 Blower Motor.

Shingadaddy · July 29

mikeyk101

Thanks so much for the reply. At least I now know if it was a legit post or if I goofed something somewhere!

Yes todays vehicles are complex beasts. But it looks like newdude took that as a challenge and threw the book at it!

newdude

I very much appreciate that you took some time to look that one up !

Definately more here than something off the top of ones head.

"Did I read codes"

No scanner to that level yet but thats about to change. No actually I have just completed the AC condenser replacement due to the standard top weld freon leak on the driver side of the condenser. It only took EYEBALLS that worked ( with glasses anyway) to see where the leak was. Lasted 7 years so I guess thats not TERRIBLE according to what i see out here.

THAT went perfect. Replaced it, Vacuumed it enough to leave it overnight to confirm holding vacuum. Vacuumed for 50 minutes and recharge with 1.2 LB of R1234yF. (Weighed in) . Blew NICE COLD AIR that night.Got up next morning and made it half way to work with awesome coolness and BLOWER QUIT (???? This is my typical luck....)

Noticed compressor off also. Freon charge still looked good. Took the most logical first and after fuse checks, removed blower (easy actually) figuring if blower was goofy the K33 would probaly inhibit the compressor. Probably right looks like.

Inspeced blower and REALLY AMAZED at the RUST and corrosion in it. On CIrcuit board. Looks like a cap blew and spewed eletrolye all over and ate it up. I'll check the drain hose too if I can find it but the entire inside of that area is dry and clean.

WIth original motor in - Looked at PWM line with scope and it was always low. BLower not supplying a pull up. (BAD BLOWER FOR SURE) Got a 4 seasons 75039 and put it in. Notice compresor on and tried blower to find it going in fits and start and not running at ALL consistent. Pull up voltage with K33 disconnected is 3VDC from motor. I figure probably a new microprocessor running at 3.3VDC. With K33 in it drops to 2 VDC (?) and I see it being PWM'd at about 30 HZ and only 2 volts peak. PWM duty cycle responding in sync with control panel fan speed knob.

By the looks of the post you supplied - I probably need a new K33. Which means I need to program it. Which means a GM Mongoose is probably in my near future.

If its okay that I ask - is the troubleshooting data in the post from Alldata, Mitchells or the GM SUBSCRIPTION TECH DATA.

Thank you very much !

And any guidance in addition to or other than what I figure is the path forwrd - feel free to toss it in here.

newdude · July 29

11 hours ago, Shingadaddy said:

mikeyk101

Thanks so much for the reply. At least I now know if it was a legit post or if I goofed something somewhere!

Yes todays vehicles are complex beasts. But it looks like newdude took that as a challenge and threw the book at it!

newdude

I very much appreciate that you took some time to look that one up !

Definately more here than something off the top of ones head.

"Did I read codes"

No scanner to that level yet but thats about to change. No actually I have just completed the AC condenser replacement due to the standard top weld freon leak on the driver side of the condenser. It only took EYEBALLS that worked ( with glasses anyway) to see where the leak was. Lasted 7 years so I guess thats not TERRIBLE according to what i see out here.

THAT went perfect. Replaced it, Vacuumed it enough to leave it overnight to confirm holding vacuum. Vacuumed for 50 minutes and recharge with 1.2 LB of R1234yF. (Weighed in) . Blew NICE COLD AIR that night.Got up next morning and made it half way to work with awesome coolness and BLOWER QUIT (???? This is my typical luck....)

Noticed compressor off also. Freon charge still looked good. Took the most logical first and after fuse checks, removed blower (easy actually) figuring if blower was goofy the K33 would probaly inhibit the compressor. Probably right looks like.

Inspeced blower and REALLY AMAZED at the RUST and corrosion in it. On CIrcuit board. Looks like a cap blew and spewed eletrolye all over and ate it up. I'll check the drain hose too if I can find it but the entire inside of that area is dry and clean.

WIth original motor in - Looked at PWM line with scope and it was always low. BLower not supplying a pull up. (BAD BLOWER FOR SURE) Got a 4 seasons 75039 and put it in. Notice compresor on and tried blower to find it going in fits and start and not running at ALL consistent. Pull up voltage with K33 disconnected is 3VDC from motor. I figure probably a new microprocessor running at 3.3VDC. With K33 in it drops to 2 VDC (?) and I see it being PWM'd at about 30 HZ and only 2 volts peak. PWM duty cycle responding in sync with control panel fan speed knob.

By the looks of the post you supplied - I probably need a new K33. Which means I need to program it. Which means a GM Mongoose is probably in my near future.

If its okay that I ask - is the troubleshooting data in the post from Alldata, Mitchells or the GM SUBSCRIPTION TECH DATA.

Thank you very much !

And any guidance in addition to or other than what I figure is the path forwrd - feel free to toss it in here.

GM subscription but Mitchell and Alldata should have this as well. GM also has lots of electrical data in the gmupfitter website too like connector ends and schematics.

I'd verify all the circuits for the HVAC control module.

Shingadaddy · July 29

Thanks again newdude! Yes GMUpfitter is where I got the schematics I am using as a reference actually. I put this NEW Four Seasons blower motor in after not seeing pullup from original motor on pin 2. Before installing it I hooked JUST the power and ground up to it and it pulled pin 2 up to 3v and some change... All powers and grounds to this new motor are clean and solid. I hooked up the control pin 2 to the HVAC module, saw a 1 volt drop in the pull up ( now 2 VDC), Good looking Squared off ,variable duty cycle PWM (I guess) and I got SPASTIC/ start / stop RPM nonsense. But during that *nonsense* I see a good solid power and ground and a 2Volt peak PWM on the control line with NO SPASTICNESS in the signal.... ???????

Perplexed - I went and swapped the blower for a another new one and got the dreaded SAME RESULT thing???

I think I might bench test this Four Seasons blower because I have at my disposal - all sorts of electronic goodies and PWM is something I design in to lots of stuff so that's not a far from reach on my bench... Might be a day or 2 before I get to it but I'll report what I find. Reading the diag data again that you provided seems to suggest anything over 1VDC should be okay on the control line if I read it right. Tis is my daily life. I always seem to fall into the weirdest circumstances.....

Shingadaddy · August 4

Okay well.... 2 volt Peak is apparently on the edge of NOT ENOUGH and My bench tests shows the blower motor responds to a good 3 Volt peak PWM signl completely fine. I thInk the 2 volt signal was near right on the edge of working but not quite enough. Thats why I occasionally saw the motor Jerk around and run for fractions of a second but only while the engine was running. Most likely due to a little bit of signal noise spikes on the power or signal line.

I have a small TEST PCB with an STmicro on it that I can code up any PWM necessary and thats what I used to drive the PWM directly into the motor with the HVAC module unplugged.(Brown connetor J2 I think it was...) The motor harness was still plugged in so the motor got battery power as needed.

This points to a damaged HVAC module or harness wiring. That wiring is pretty simple and mostly in view right in front of you while the glovebox out and the HVAC module hanging loose. I did a video of the signal levels that dont work but its on my phone and I'm lacking the method to post it here. Besides its probably way to big anyway. I'll poke around with the wiring and do the resistance checks just to be more sure but --- probably a HVAC module and some programming path I have yet decided to take. Thank you folks for the help!

Shingadaddy · August 23

Well.... This has been QUITE the circle. So with 7 or 8 GM vehicals in the fam, and me being the one who trys to support all those, I was perfectly willing to accept that I was going to get a module programming solution to use for this task. I Popped for a Mongoose Plus GM. Story goes that they are Fully GM approved and dealers are using them as well as the MDI/MDI2 Bosch units. So far - that has been smooth sailing.I got a new GM K33 HVAC control module from GM GMPartsOutlet.net. Got that and 2 variable valve timing control solenoids for a 2013 Malibu 2.0 turbo. in about 4 or 5 days at normal shipping costs. (Not accelerated) . Used the Mongoose Flawlessly after a GM SPS subsciption and POOF!

Yep! SAME ISSUE WITH THE SECOND 4 SEASONS 75039 BLOWER MOTOR AND THE NEW K33! Oddball fits and starts and goofy operation. This is the motor blower motor I tested on the bench with a good 3 volt peak amplitude PWM signal. And THERE - IT WORKED.

Out comes the O scope again. I see a 3Volt solid signal being pulled up by the blower motor on the PWM line.

UNTIL I PUT THE KEY IN THE IGNITION!

Then I see it DROP to 2 volts. (?) AFter about 20 seconds or so - IT GOES BACK UP TO 3 VOLTS! I start the truck and it goes BACK to 2 volts.... ????? THAT is not some oddball bad connection as far as I can tell. Something somewhere is programatically driving the output of the K33 to do that. And ALL PWM settings show variable pulse width but only 2 volts peak!

Okay so THAT BLOWER MOTOR works with 3v but NOT WITH 2v. Just to make sure i 'm not a D/A, I have the original blower and repower it and there is NO PULL UP VOLTAGE coming from it on the PWM line like it should. SO I KNOW THE ORIGINAL BLOWER IS BAD. So The SECOND 4 seasons blower goes back and I get a refund!

I then orderd a OEM HVAC blower from the GMPartsOutlet.net folks and it arrives. I put it in and it works ---------- PERFECT.

BEWARE - The 4 Seasons blower 75039 that claims to be compatible with 2017 GMC Sierra Crew cab 4WD 5.3 trucks ---- and is prolificlly listed by many suppliers as compatible -

APPARENTLY DOES NOT WORK WITH THEM ALL! I've tried 2.

I have been fiddling with this new OEM blower all evening and it works consistently in all settings. The dash is about 75 % back together but the mosquitoes starting winning that battle before I got done.

Pretty sure at LEAST the 2016 would be the same situation.

Thats what I have as first hand experience so --- just be aware.

Edited August 23 by Shingadaddy
Clarity

Shingadaddy · August 25

Well the truck was left at the 75% complete level and we took about a 120 mile round trip. That included some mild off road activity back in the woods to a cold clear creek for all 9 grandkids (Well 1 rented so to speak) to swim in and cool off.

Zero issues

No Bisbehaving

COLD AC..

So the truck is now - this morning - back 100% together including the one extremely hard to get to screw in the very front right corner of the lower cover. Hot glue to the rescue to hold the screw in the socket to get it started.

2 things that bother me along this whole blower K33 journey.

1. I left no fewer that 2 web inquiries and 2 phone messages with 4 Season - which has a couple of different names associated with it. I NEVER GOT A REPLY! I called a different number that showed up on some related web page for 4 Seasons and talked to a guy named Keith I believe. He was not technical and what I told him seemed to perplex him but at least he answered the phone. NOT GOOD CUSTOMER SERVICE. Not his fault.

2. At the time - This 75039 is/was advertised by multiple outlets - including 4 seasons - as the 4 season blower for 2017 GMC Sierra replacements.

The 2 I tried DO NOT WORK CORRECTLY . An OEM replacement works as expected without issue.

Thanks for the interaction folks.

mikeyk101 · August 25

Not trying to rap you but I am assuming you picked a Four Seasons because it was cheaper than OEM? If that's the case, from personal experience, I have found that many parts on these truly need to be replaced with OEM parts. Not all but many mechanical or electronic parts. They just tend to work the first time and end up being less headaches. Cosmetic stuff is usually no big deal but stuff like a blower, I no longer even try to find cheaper aftermarket stuff. Now, I will search for the best price I can for OEM parts because they are sometimes all over the place for pricing.

Shingadaddy · August 26

Certainly not bad advice. It was about $10.00 cheaper and the reason I tried it was I could get it THAT DAY!.

At the time that mattered but it was a bust due to the blower. Use another vehicle for that trip.

BLower came from Autozone. THEY were pleasant and unarguementative about the hassle it caused and refunded me no quesions. They DID have one (DURALAST GOLD) that was about 40 cheaper than OEM but when the box was opened - the fan inside didn't even resemble the one pictured on the BOX! That spooked me so I thought I bought UP from there. The Autozone blower might work fine. THAT WOULD BE MY LUCK for sure.

I've found that over the years - ONLINE GM prices from various sources are usually anywhere from about 25 - 60% cheaper and many can be had within 3 to 5 days. They wanted $313 for this blower at the dealership. $185 I had it it about 5 days.

Those games haven't change over a lot of years.

AndI wouldn't be a bit surprised that auto makers do this little trick to ensure exact replacement more often