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2001 C5 Z06 M6
HVAC unit is automatic I believe
HVAC unit doesn’t work. Nothing lights up and no buttons work. It seems completely dead.
When I plug/unplug the unit I can hear something actuating in the dashboard
Tested fuse #18 and #27 with the key in the ON position and both read 11.8V
Codes are HVAC NO COMMS and B0090
Whats the next step?
NOT a dumb question and we see a lot of members here on the Forum that hate “electrical” too so you’re not the only one…a lot of pros I’ve seen are weak as well….the ground has to carry the current in that circuit back to the battery so you use a “load” like a 12 volt INCANDESCENT test light or an old headlight bulb to check…if I know the current is 5 amps like on a fuel pump I’ll use a bulb that draws 5 amps…if the bulb is bright the ground is good…so what you can do is remove the HVAC module and remove the connector…take your test light and connect it to power preferably at battery positive…now touch the tip of the test light to the black wire terminal on the connector…if ground is good the light will be bright…pictured is my 1 amp and 5 amp test lights…BTW the black/white wire gets it’s ground from the body ground G202 internally within the HVAC module…the 5 volt reference circuits you see gets pulled to ground through the sensors pictured so it will be less than 5 volts…also check the orange wire terminal for system voltage after you’ve confirmed that you have power to the fuse and the fuse is not blown…if powers and grounds are good it’s most likely a bad HVAC module.
NOT a dumb question and we see a lot of members here on the Forum that hate “electrical” too so you’re not the only one…a lot of pros I’ve seen are weak as well….the ground has to carry the current in that circuit back to the battery so you use a “load” like a 12 volt INCANDESCENT test light or an old headlight bulb to check…if I know the current is 5 amps like on a fuel pump I’ll use a bulb that draws 5 amps…if the bulb is bright the ground is good…so what you can do is remove the HVAC module and remove the connector…take your test light and connect it to power preferably at battery positive…now touch the tip of the test light to the black wire terminal on the connector…if ground is good the light will be bright…pictured is my 1 amp and 5 amp test lights…BTW the black/white wire gets it’s ground from the body ground G202 internally within the HVAC module…the 5 volt reference circuits you see gets pulled to ground through the sensors pictured so it will be less than 5 volts…also check the orange wire terminal for system voltage after you’ve confirmed that you have power to the fuse and the fuse is not blown…if powers and grounds are good it’s most likely a bad HVAC module.
Okay so I’ve done some testing. To start, I used a 6V/12V tester light from a parts store. I tried multiple stores and could not find a 12V only tester. I’m also not entirely sure if it’s LED or incandescent. None had labels and I couldn’t find any on Amazon that were not LED.
To start, the orange wire into the HVAC module is 10.7V compared to the 11.8V at the fuse under the passenger dashboard. I tested the ground by connecting the test light to the car battery and then probing the ground, and the test light was bright. So, what now? Is the 10.7V not enough? If so, how do you fix that?
So you have a 1.1 volt drop from the fuse box to the connector...way to much...looking at the wiring schematic in post #3 there is no connector in between fuse 27 to the harness and it's just a straight shot...what you can and since you don't have any piercing probes find yourself a sharp pin and pierce the wire an inch or so upstream of the connector and then check the voltage...there may some corrosion at C12 where you are seeing 10.7 volts...what are you seeing at C5 which is the brown wire ??...that is powered with the key ON...that comes from fuse 18...every module usually has 2 power sources...a "key on" which is the "wakeup" signal and "hot at all times" which comes directly from the battery...since there is no connector you may have to get into the fusebox (see below)…what you can try if you want is hook the connector back up an if you can backprobe C12 and feed 12 volts into that wire and see if the module powers up...just a thought…the LED test lights are “computer safe” and draw very little current but the test lights with a bulb draw a little more current.
So you have a 1.1 volt drop from the fuse box to the connector...way to much...looking at the wiring schematic in post #3 there is no connector in between fuse 27 to the harness and it's just a straight shot...what you can and since you don't have any piercing probes find yourself a sharp pin and pierce the wire an inch or so upstream of the connector and then check the voltage...there may some corrosion at C12 where you are seeing 10.7 volts...what are you seeing at C5 which is the brown wire ??...that is powered with the key ON...that comes from fuse 18...every module usually has 2 power sources...a "key on" which is the "wakeup" signal and "hot at all times" which comes directly from the battery...since there is no connector you may have to get into the fusebox (see below)…what you can try if you want is hook the connector back up an if you can backprobe C12 and feed 12 volts into that wire and see if the module powers up...just a thought…the LED test lights are “computer safe” and draw very little current but the test lights with a bulb draw a little more current.
Let me back up a minute and add clarification. When the key is in the off position the voltage at the orange wire is 11.2V. When the key is turned to the on position the voltage at the orange wire is 10.7V. When the key is turned to the on position the brown wire is 11.8V.
If you have 11.2 at the orange wire what is the voltage at the fuse ??…even at 11.2 volts that should be OK…I’d say you need a new module if all the powers and grounds are good…I might want you to do something else…to the left of the BCM next to the fusebox you’ll see 2 white splice packs…one has 4 wires and the other has 9 I think…pop off the gray cap (arrow) off it…it look like a comb…take sandpaper to that comb and reinstall…if that comb has corrosion you can get a no comm…the HVAC module is one of those wires.
If you have 11.2 at the orange wire what is the voltage at the fuse ??
Fuse #18 under the passenger floorboard shows 0V with the key off and 11.8V with the key on.
Fuse #27 under the passenger floorboard shows 11.8V with the key off or on.
I will clean the splice pack and see if that fixes the issue.
Well since you didn’t even have a DVOM the way I’d do this is have the HVAC connector plugged in…the “open circuit “ voltage test you did is not the best way…go to Staples and get some T pins…watch how to backprobe video…with the HVAC module plugged in take one lead of the DVOM and connect to the battery positive post…now backprobe the orange B+ wire…you should see NO more than .5 volts….that means the voltage is dropping .5 volts from the battery to the connector…do this on the ground side also….one lead on battery negative and other lead back probed into the ground connector at the HVAC module…if you see a negative number just switch the leads around…the number you see is more important !!…now with these cars getting older you’ll see some more electrical problems so learning this electrical stuff will really help…there are some good videos on YouTube you can watch.
Sorry it’s been a bit. Had some other things to take care of. Here are my results from testing. Everything was done with the key out of the ignition.
Tools are T-pins, multimeter, and alligator clip with 5 feet of wire between them.
1. Used multimeter lead to measure voltage between orange wire and body ground in RF of cabin. I stuck the lead in the opening of the connector where the HVAC module would plug in. Measured 11.5 V.
2. Used T pin to back probe orange wire in connector and measured voltage WITHOUT HVAC module plugged in. Voltage was 11.5 V confirming I was back probing correctly.
3. With T pin still in place I plugged in the HVAC module. I remeasured and the voltage with the module plugged in was 3.2V.
4. Double checked by measuring battery positive terminal to back probed T pin and measured -8.3 V
5. Unplugged HVAC module, remeasured back probed T pin and voltage returned to 11.5V confirming I was still back probing correctly.
6. Back probed ground wire and measured T pin to negative battery terminal with HVAC module unplugged. Voltage measured 0.6 mV.
7. Plugged in HVAC module and remeasured ground. Still measured 0.6 mV.
Plugging in the HVAC module causes an 8.3 V drop at the orange wire.
Sorry it’s been a bit. Had some other things to take care of. Here are my results from testing. Everything was done with the key out of the ignition.
Tools are T-pins, multimeter, and alligator clip with 5 feet of wire between them.
1. Used multimeter lead to measure voltage between orange wire and body ground in RF of cabin. I stuck the lead in the opening of the connector where the HVAC module would plug in. Measured 11.5 V.
2. Used T pin to back probe orange wire in connector and measured voltage WITHOUT HVAC module plugged in. Voltage was 11.5 V confirming I was back probing correctly.
3. With T pin still in place I plugged in the HVAC module. I remeasured and the voltage with the module plugged in was 3.2V.
4. Double checked by measuring battery positive terminal to back probed T pin and measured -8.3 V
5. Unplugged HVAC module, remeasured back probed T pin and voltage returned to 11.5V confirming I was still back probing correctly.
6. Back probed ground wire and measured T pin to negative battery terminal with HVAC module unplugged. Voltage measured 0.6 mV.
7. Plugged in HVAC module and remeasured ground. Still measured 0.6 mV.
Plugging in the HVAC module causes an 8.3 V drop at the orange wire.
To me it loooks like your are shorting the batteryvoltage from fuse 27 when your connecting the HVAC unit to the Connector probably due internal faileure on the HVAC module .
You probably have to buy another module , but It would not hurt (IMO) and take the module apart shown below like I did when I installed new LED's to improve the lights in the module and look for any damaged componentes .
To me it loooks like your are shorting the batteryvoltage from fuse 27 when your connecting the HVAC unit to the Connector probably due internal faileure on the HVAC module .
You probably have to buy another module , but It would not hurt (IMO) and take the module apart shown below like I did when I installed new LED's to improve the lights in the module and look for any damaged componentes .
Originally Posted by sdcdubv
Sorry it’s been a bit. Had some other things to take care of. Here are my results from testing. Everything was done with the key out of the ignition.
Tools are T-pins, multimeter, and alligator clip with 5 feet of wire between them.
1. Used multimeter lead to measure voltage between orange wire and body ground in RF of cabin. I stuck the lead in the opening of the connector where the HVAC module would plug in. Measured 11.5 V.
2. Used T pin to back probe orange wire in connector and measured voltage WITHOUT HVAC module plugged in. Voltage was 11.5 V confirming I was back probing correctly.
3. With T pin still in place I plugged in the HVAC module. I remeasured and the voltage with the module plugged in was 3.2V.
4. Double checked by measuring battery positive terminal to back probed T pin and measured -8.3 V
5. Unplugged HVAC module, remeasured back probed T pin and voltage returned to 11.5V confirming I was still back probing correctly.
6. Back probed ground wire and measured T pin to negative battery terminal with HVAC module unplugged. Voltage measured 0.6 mV.
7. Plugged in HVAC module and remeasured ground. Still measured 0.6 mV.
Plugging in the HVAC module causes an 8.3 V drop at the orange wire.
Okay so I’m back again. I sourced a new HVAC module. The module does work. I saw it operating. I plug it into the car and…nothing. Module didn’t light up, no response, nothing. So given what’s been outlined in the thread so far and now knowing it’s not the hvac module, what could be causing this? @C5 Diag & @oelarse
Plug the HVAC connector in and let’s take a t pin and back probe that orange power wire…let’s take 12 volts and power that module directly…see if it works…if it does you have high resistance somewhere in that wire…just checking for 12 volts at the connector doesn’t really tell you much.
Plug the HVAC connector in and let’s take a t pin and back probe that orange power wire…let’s take 12 volts and power that module directly…see if it works…if it does you have high resistance somewhere in that wire…just checking for 12 volts at the connector doesn’t really tell you much.
Alright so if I’ve got this right I take a T-pin and back probe the orange wire at the plug in, then take another wire and run it from the T-pin to the battery. Then turn the key and see if it comes on?
Alright so if I’ve got this right I take a T-pin and back probe the orange wire at the plug in, then take another wire and run it from the T-pin to the battery. Then turn the key and see if it comes on?
Yes, let’s give the HVAC module a good power source !!…didn’t you say the module is definitely good ??
HVAC No Comms
