GMC Sierra: Stuck On Defrost
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Date: 2021-03-15
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Comments and reviews: 9
Nicholas
GM had some absolutely terrible software during this gen 3 time. The PCM in my 2000 Sonoma is absolutely intolerant of any difference in the IAC position counts or else the idle will hang and the spark timing will oscillate between the two different spark tables. The throttle cracker calculates IAC counts based on RPM, not based on TPS input so it can hang at a high idle in some circumstances until you bring the car to a stop and it would then switch modes into PID control. Even after fixing the IAC issue the RPM will still randomly hang from time to time when I clutch in. And solving these problems is next to impossible without forensics I had to use HPTuners and go on the tuning forums to figure out why it was happening.
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GM had some absolutely terrible software during this gen 3 time. The PCM in my 2000 Sonoma is absolutely intolerant of any difference in the IAC position counts or else the idle will hang and the spark timing will oscillate between the two different spark tables. The throttle cracker calculates IAC counts based on RPM, not based on TPS input so it can hang at a high idle in some circumstances until you bring the car to a stop and it would then switch modes into PID control. Even after fixing the IAC issue the RPM will still randomly hang from time to time when I clutch in. And solving these problems is next to impossible without forensics I had to use HPTuners and go on the tuning forums to figure out why it was happening.
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Black3ternity
Great Video.
One thing I observe though:
When you moved it back to panel I can see the slot is stopping before it hits the lever peg.
I have no clue how it's SUPPOSED to look, but I could imagine that the pitentiometer is probably in there with one or two teeth misaligned? Seems to me the whole plate is off so it never reaches the panel end and thus overturns on the other side. Edit says: See 27: 05 for what I mean.
Hope you know what I mean. Not sure if this would be fixable - but I think your hack is proper and helps it. Like others said: When the customer fixes the doors, just unscrew it and you have your full range back. Great job!
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Great Video.
One thing I observe though:
When you moved it back to panel I can see the slot is stopping before it hits the lever peg.
I have no clue how it's SUPPOSED to look, but I could imagine that the pitentiometer is probably in there with one or two teeth misaligned? Seems to me the whole plate is off so it never reaches the panel end and thus overturns on the other side. Edit says: See 27: 05 for what I mean.
Hope you know what I mean. Not sure if this would be fixable - but I think your hack is proper and helps it. Like others said: When the customer fixes the doors, just unscrew it and you have your full range back. Great job!
reply
WreckDiver99
22 Year old Tahoe here. in Michigan. Still running, and unfortunately has lived outside for the past 15 or so years. Having HVAC issues as well. Looks like I'm in for a a new blower (squeals like the guy from Deliverance, and new resistor (I have two speeds, OFF and balls out. I will say that my doors move SUPER slow or get stuck. Once in a while you get THUNK when it figures out to change the door location. This is a good video for future fixes.
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22 Year old Tahoe here. in Michigan. Still running, and unfortunately has lived outside for the past 15 or so years. Having HVAC issues as well. Looks like I'm in for a a new blower (squeals like the guy from Deliverance, and new resistor (I have two speeds, OFF and balls out. I will say that my doors move SUPER slow or get stuck. Once in a while you get THUNK when it figures out to change the door location. This is a good video for future fixes.
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Dillon
I just replaced an HVAC module in mine because it stopped communicating and got stuck on the Face Position. Which it manages to go to by default when I shut it off. The Tech 2 Couldn't talk to it at all. I suspected the fuses but it had power at the HVAC module.
If it stayed on the Defrost/Floor I wouldn't have cared because I don't ever change the mode position even on the hottest or coldest day but the temperature was stuck aswell.
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I just replaced an HVAC module in mine because it stopped communicating and got stuck on the Face Position. Which it manages to go to by default when I shut it off. The Tech 2 Couldn't talk to it at all. I suspected the fuses but it had power at the HVAC module.
If it stayed on the Defrost/Floor I wouldn't have cared because I don't ever change the mode position even on the hottest or coldest day but the temperature was stuck aswell.
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Michael
I have a blend door actuator out in my vehicle right now. Might is the automatic type system. Whenever you start up the vehicle, it sits there making a popping noise. I tried resetting it by pulling the fuse and it just made the problem worse. To make things even more of a pain, there is a dash brace that sits right in front of the actuator which makes replacing it almost impossible without removing the dash.
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I have a blend door actuator out in my vehicle right now. Might is the automatic type system. Whenever you start up the vehicle, it sits there making a popping noise. I tried resetting it by pulling the fuse and it just made the problem worse. To make things even more of a pain, there is a dash brace that sits right in front of the actuator which makes replacing it almost impossible without removing the dash.
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Gplus
Its a massive job (probably easier in that truck than in my Audi) to replace some 2 Armaflex foam on the blend doors. But the result will be night and day.
(in my Audi the heater core is always on and it depends on blend doors sealing properly to mix hot and cold air. Heater core and ac were perfectly fine but it would neither cool nor heat correctly)
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Its a massive job (probably easier in that truck than in my Audi) to replace some 2 Armaflex foam on the blend doors. But the result will be night and day.
(in my Audi the heater core is always on and it depends on blend doors sealing properly to mix hot and cold air. Heater core and ac were perfectly fine but it would neither cool nor heat correctly)
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JK
Someone forgot to program an out of range error function for that A/D conversion in the control head. It does seem they do stop the motor when the get a repeated value. But that out of range for greater than 5v doesn't compute when the controller is called to go back. Of course, the programmers never saw one of the air boxes with degraded foam seals.
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Someone forgot to program an out of range error function for that A/D conversion in the control head. It does seem they do stop the motor when the get a repeated value. But that out of range for greater than 5v doesn't compute when the controller is called to go back. Of course, the programmers never saw one of the air boxes with degraded foam seals.
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Willie
You were right on track (no pun intended) It sure looked like the controller didn t like the signal it was getting from the door sensor (out of range) I wonder if ya were to solder a resistor in the defrost circuit to keep the voltage from going out of range? or a zener diode to bleed off anything over 5 volts?
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You were right on track (no pun intended) It sure looked like the controller didn t like the signal it was getting from the door sensor (out of range) I wonder if ya were to solder a resistor in the defrost circuit to keep the voltage from going out of range? or a zener diode to bleed off anything over 5 volts?
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CarCrankTime
I think that most actuators work the same way, like blend doors on your case.
Iwe saw intake flap motors out of range doing the same thing, Turbo actuators VNT, Tps. Mostly on VW and Mercedes Renaults.
All the best man! You are the right person for young people to learn from! And old: )
Cheers
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I think that most actuators work the same way, like blend doors on your case.
Iwe saw intake flap motors out of range doing the same thing, Turbo actuators VNT, Tps. Mostly on VW and Mercedes Renaults.
All the best man! You are the right person for young people to learn from! And old: )
Cheers
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