AC display went out, Weird coincidence?
Thread Starter
Racer
Joined: Jul 2008
Posts: 306
Likes: 0
From: Riverside CA
AC display went out, Weird coincidence?
I have 2004 C5 that threw the AC belt, ac was working before this, and afterwards the lights still came on and you could hear the compressor trying to work.(clicking)
i found that the AC idler pully gave out, I had heard other squeaking so replaced all the parts, i got new belts, idler pulleys, and the tensioner pulleys for the whole front of engine.
my neighbor and I installed them, and the car runs fine and better, No more squeaks.
then i go to try the AC panel, and nothing, then look and see that it's completely dark, no display at all.
i did check the fuse(*#24), and it was fine, there was a relay also,(*#34) but i don't know how to test it. (*numbers of the fuses under the hood)
it's like the panel isn't getting power. and of course, it happens while the weather is in the 90's
are there any other fuses to check? like in the footwell?
thank you for your help.
i found that the AC idler pully gave out, I had heard other squeaking so replaced all the parts, i got new belts, idler pulleys, and the tensioner pulleys for the whole front of engine.
my neighbor and I installed them, and the car runs fine and better, No more squeaks.
then i go to try the AC panel, and nothing, then look and see that it's completely dark, no display at all.
i did check the fuse(*#24), and it was fine, there was a relay also,(*#34) but i don't know how to test it. (*numbers of the fuses under the hood)
it's like the panel isn't getting power. and of course, it happens while the weather is in the 90's
are there any other fuses to check? like in the footwell?
thank you for your help.
Melting Slicks
Joined: Jul 2004
Posts: 3,294
Likes: 482
From: Brea CA
The HVAC panel has a know issue with a set of resistors that are poorly soldered to the circuit board. These cause the dim display issue/no display.
All HVAC related fuses are in the fuse block in the passenger foot well. Only fuse in the under hood fuse block is for the AC clutch.
You can turn the AC on and it should blow cold out of the vents (turn the drivers temp **** CCW for several turns) and push the fan button up). This will at least tell you it is working.
I have done the repair on many of these units over the years. Easy to do but does require some skill in soldering.
Gary
All HVAC related fuses are in the fuse block in the passenger foot well. Only fuse in the under hood fuse block is for the AC clutch.
You can turn the AC on and it should blow cold out of the vents (turn the drivers temp **** CCW for several turns) and push the fan button up). This will at least tell you it is working.
I have done the repair on many of these units over the years. Easy to do but does require some skill in soldering.
Gary
Thread Starter
Racer
Joined: Jul 2008
Posts: 306
Likes: 0
From: Riverside CA
Hi Gary
I'm Gary too.
i was checking the wrong fuse, DOH!
I'll check the fuse in the foot well on Saturday.
when i bought this c5, it was having the lighting issue,
that was 1 of the first things i fixed.
Thank you
I'm Gary too.
i was checking the wrong fuse, DOH!
I'll check the fuse in the foot well on Saturday.
when i bought this c5, it was having the lighting issue,
that was 1 of the first things i fixed.
Thank you
Thread Starter
Racer
Joined: Jul 2008
Posts: 306
Likes: 0
From: Riverside CA
i checked all the fuses today, and all looked good, and still no power.
i had a job to go to about 15 miles from here, in Moreno Valley,
and at about 10 miles it just comes back on and worked.
when i left the job, it didn't work again, no power.
and about 5 miles later it started again,
then did some grocery shopping on the way home,
got back in the car, and no power again., but while sitting there about a minute, it came on again,
i'm thinking maybe it's a loose connection? but where?
I'm stumped at this point.
i had a job to go to about 15 miles from here, in Moreno Valley,
and at about 10 miles it just comes back on and worked.
when i left the job, it didn't work again, no power.
and about 5 miles later it started again,
then did some grocery shopping on the way home,
got back in the car, and no power again., but while sitting there about a minute, it came on again,
i'm thinking maybe it's a loose connection? but where?
I'm stumped at this point.
Melting Slicks
Joined: Jul 2004
Posts: 3,294
Likes: 482
From: Brea CA
Do you have an issue with Traction Control/Active Handling not turning on when you start the car? I have see the Active Handling/Traction control throwing errors and the HVAC controller dead at startup. Both are on the same switched circuit on the ignition switch.
I would pull the ignition switch and clean the contacts inside of it. This has fixed several cars I have come across.
Gary
I would pull the ignition switch and clean the contacts inside of it. This has fixed several cars I have come across.
Gary
Safety Car
Joined: Mar 2017
Posts: 3,771
Likes: 940
From: Orlando Florida
I’m with SilverC54me, have to wonder if this might not be yet another ignition switch issue. Something happens where current takes some time to get through carbonized contacts.
Last edited by redzg; Jul 13, 2025 at 07:03 AM.
Thread Starter
Racer
Joined: Jul 2008
Posts: 306
Likes: 0
From: Riverside CA
Do you have an issue with Traction Control/Active Handling not turning on when you start the car? I have see the Active Handling/Traction control throwing errors and the HVAC controller dead at startup. Both are on the same switched circuit on the ignition switch.
I would pull the ignition switch and clean the contacts inside of it. This has fixed several cars I have come across.
Gary
I would pull the ignition switch and clean the contacts inside of it. This has fixed several cars I have come across.
Gary
that was next on my list of items to fix.
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Tech Contributor
Joined: Jan 2007
Posts: 19,493
Likes: 1,178
From: Dyer, IN
There should be some other corroborating DTCs.
Melting Slicks
Joined: Jul 2004
Posts: 3,294
Likes: 482
From: Brea CA
Ok, but where are the other symptoms? If that contact was dead for that amount of time rendering the HVAC control and EBCM dead, it would also impact the back up lights, O2 heater circuits, Rear defog, rear view mirror, etc.
There should be some other corroborating DTCs.
There should be some other corroborating DTCs.
Not all lighting circuits do not run through the ignition switch and would not be affected by this.
The EBCM and HVAC pull the most current on this circuit when powered on. You will get No Communication message when checking codes. If your car has F45 or F55 there also should be a No Communication message.
Gary
Tech Contributor
Joined: Jan 2007
Posts: 19,493
Likes: 1,178
From: Dyer, IN
There are 2 circuits coming off the ignition switch. Accessory and ON/Start. The issue experienced with lilmonster's car is on the Accessory side of the switch. It is not that there is no power getting to these devices, it is that there is a large voltage drop across this set of contacts causing these devices not to operate properly. There are some devices that even with a large voltage drop in the circuit will still operate just enough to seem to be working properly.
Not all lighting circuits do not run through the ignition switch and would not be affected by this.
The EBCM and HVAC pull the most current on this circuit when powered on. You will get No Communication message when checking codes. If your car has F45 or F55 there also should be a No Communication message.
Gary
The EBCM and HVAC pull the most current on this circuit when powered on. You will get No Communication message when checking codes. If your car has F45 or F55 there also should be a No Communication message.
Gary
Thread Starter
Racer
Joined: Jul 2008
Posts: 306
Likes: 0
From: Riverside CA
sorry it took me so long to get back here.
I finally got the code list, and it's kinda long.
also i'm thinking the switch too now, because while trying to get the codes,
the key was having issues, then barely touch the key and it all waked up.
here's the code list i got, i also cleared the list to see what comes back .
PCM
P0442 Evaporative Emission (EVAP) System Small Leak Detected
P0856 not found
P1689 Traction Control Delivered Torque Output Circuit
C1277 Requested Torque Signal Circuit Malfunction
BCM
B0432 Rear Defogger Relay Circuit
B2721 PASS-Key Detection Circuit
B2723 PASS-Key Detection Circuit
U1040 Loss of Communications with TCS
B0516 Speedometer Signal Circuit Malfunction
U1040 Loss of Communications with TCS
HVAC
B0361 Left Actuator Feedback Short to GND
B0441 Left Actuator Out of Range
i'll take it for a drive in the next couple days to see what codes come back.
I finally got the code list, and it's kinda long.
also i'm thinking the switch too now, because while trying to get the codes,
the key was having issues, then barely touch the key and it all waked up.
here's the code list i got, i also cleared the list to see what comes back .
PCM
P0442 Evaporative Emission (EVAP) System Small Leak Detected
P0856 not found
P1689 Traction Control Delivered Torque Output Circuit
C1277 Requested Torque Signal Circuit Malfunction
BCM
B0432 Rear Defogger Relay Circuit
B2721 PASS-Key Detection Circuit
B2723 PASS-Key Detection Circuit
U1040 Loss of Communications with TCS
B0516 Speedometer Signal Circuit Malfunction
U1040 Loss of Communications with TCS
HVAC
B0361 Left Actuator Feedback Short to GND
B0441 Left Actuator Out of Range
i'll take it for a drive in the next couple days to see what codes come back.
Melting Slicks
Joined: Jul 2004
Posts: 3,294
Likes: 482
From: Brea CA
Based on the codes listed, I have put suggested solutions next to each.
Gary
Gary
sorry it took me so long to get back here.
I finally got the code list, and it's kinda long.
also i'm thinking the switch too now, because while trying to get the codes,
the key was having issues, then barely touch the key and it all waked up.
here's the code list i got, i also cleared the list to see what comes back .
PCM
P0442 Evaporative Emission (EVAP) System Small Leak Detected - This i probably your gas cap. Clean the sealing surfaces on the cap and filler neck and see what comes back. Worst case you will need to replace the gas cap.
P0856 not found - This is related to the TCS (Traction control/active handling/abs) system.
P1689 Traction Control Delivered Torque Output Circuit - This and C1277 are a pair of codes. They will both come on when there are comm errors between the EBCM and PCM. This can be related to a bad ignition switch.
C1277 Requested Torque Signal Circuit Malfunction - See previous error.
BCM
B0432 Rear Defogger Relay Circuit - Don't worry about this one.
B2721 PASS-Key Detection Circuit - Clean the resistor pellet on your ignition key. This can also be a bad set of contacts in the ignition switch that connect to the resistor pellet.
B2723 PASS-Key Detection Circuit - see above
U1040 Loss of Communications with TCS - This can be caused by the ignition switch contacts being arced up
B0516 Speedometer Signal Circuit Malfunction - This can be anything from bad wiring from the speed sensor in the diff to the PCM to the gauge cluster.
U1040 Loss of Communications with TCS - This can be caused by the ignition switch contacts being arced up
HVAC
B0361 Left Actuator Feedback Short to GND - time to replace the blend door actuators.
B0441 Left Actuator Out of Range - see above
i'll take it for a drive in the next couple days to see what codes come back.
I finally got the code list, and it's kinda long.
also i'm thinking the switch too now, because while trying to get the codes,
the key was having issues, then barely touch the key and it all waked up.
here's the code list i got, i also cleared the list to see what comes back .
PCM
P0442 Evaporative Emission (EVAP) System Small Leak Detected - This i probably your gas cap. Clean the sealing surfaces on the cap and filler neck and see what comes back. Worst case you will need to replace the gas cap.
P0856 not found - This is related to the TCS (Traction control/active handling/abs) system.
P1689 Traction Control Delivered Torque Output Circuit - This and C1277 are a pair of codes. They will both come on when there are comm errors between the EBCM and PCM. This can be related to a bad ignition switch.
C1277 Requested Torque Signal Circuit Malfunction - See previous error.
BCM
B0432 Rear Defogger Relay Circuit - Don't worry about this one.
B2721 PASS-Key Detection Circuit - Clean the resistor pellet on your ignition key. This can also be a bad set of contacts in the ignition switch that connect to the resistor pellet.
B2723 PASS-Key Detection Circuit - see above
U1040 Loss of Communications with TCS - This can be caused by the ignition switch contacts being arced up
B0516 Speedometer Signal Circuit Malfunction - This can be anything from bad wiring from the speed sensor in the diff to the PCM to the gauge cluster.
U1040 Loss of Communications with TCS - This can be caused by the ignition switch contacts being arced up
HVAC
B0361 Left Actuator Feedback Short to GND - time to replace the blend door actuators.
B0441 Left Actuator Out of Range - see above
i'll take it for a drive in the next couple days to see what codes come back.
Tech Contributor
Joined: Jan 2007
Posts: 19,493
Likes: 1,178
From: Dyer, IN
The lock cylinder is the part that reads the key resistance. In this case, the OP may need both.
Thread Starter
Racer
Joined: Jul 2008
Posts: 306
Likes: 0
From: Riverside CA
First, I'd like to apologize the people that were helping me, for disappearing last year.
My sister (70) had stepped off a curb and broke her leg, which left her bedbound for about 4 months.
So I have been down in Vista CA taking care of her, and my 94 year old mom with Alzheimer's.
Corvette repairs kinda got back burnered for a while, but now i need to get things going again.
Now in the time i was down in Vista, it only gave me "key" issues once, i kept flipping the key and eventually it worked.
recently, it did it in my driveway, and i wondered if using another key would work, so i got my spare, and it worked first time.
so it's definitely gotta be a key and cylinder issue.
Has anyone changed there car to push button start? is it possible?
also, i seemed to figure out how to not get codes when starting the car like i use to.
When i just jumped in the car and cranked the car over, i'd get TCM and AH errors, and the A/C issues.
i found that waiting till all the bells stopped, (there are 6 when starting,)
and start the car after that, i don't have any issues and it worked fine.
i'm now also having headlight and AC blend door issues, but that's for another thread.
Thanks again for your help.
My sister (70) had stepped off a curb and broke her leg, which left her bedbound for about 4 months.
So I have been down in Vista CA taking care of her, and my 94 year old mom with Alzheimer's.
Corvette repairs kinda got back burnered for a while, but now i need to get things going again.
Now in the time i was down in Vista, it only gave me "key" issues once, i kept flipping the key and eventually it worked.
recently, it did it in my driveway, and i wondered if using another key would work, so i got my spare, and it worked first time.
so it's definitely gotta be a key and cylinder issue.
Has anyone changed there car to push button start? is it possible?
also, i seemed to figure out how to not get codes when starting the car like i use to.
When i just jumped in the car and cranked the car over, i'd get TCM and AH errors, and the A/C issues.
i found that waiting till all the bells stopped, (there are 6 when starting,)
and start the car after that, i don't have any issues and it worked fine.
i'm now also having headlight and AC blend door issues, but that's for another thread.
Thanks again for your help.
Tech Contributor
Joined: Jan 2007
Posts: 19,493
Likes: 1,178
From: Dyer, IN