AC / Anti-lock brake light issue

[CWARE]

When I got my 2 door 95 Tahoe 4wd the AC panel worked when it wanted to and I soon replaced it with a new panel as I read the stock 95 panels had many issues. The AC worked fine afterwards until last week. My wife was driving it and told me the AC had stopped working with no blower sound or air (hot or cold) coming from the vents. Later that day I checked it out hoping it was a fuse or something simple and no luck. All fuses looked fine. I then noticed that the ABS light was on in the dash. I remembered that months ago (can’t recall if it was before or after the new panel went in) the AC panel did the same thing and that the ABS light was on then also. I thought there was no way the two could be related but the next day the light was off and the AC panel worked fine.

I did some searching on the ABS light and saw some saying it could of course be the controller and some saying it could be a speed sensor at one of the wheels. Has anyone had this issue with the ABS light and AC panel being connected in some way or is this just one heck of a coincidence in my situation? Any help would be appreciated. Thanks.


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[Big Mama]

Can you read the abs code?

 

[CWARE]

I don’t have a scanner capable of running an OBD1 system.


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[Big Mama]

Ah forgot about that. I’m not great on that gen let’s get some help @swathdiver @iamdub @SnowDrifter @HiHoeSilver @Galante fellas?

 

[swathdiver]

Sorry, I'm not familiar with those. But a bi-directional scan tool is essential to properly diagnose and fix it without throwing parts at it.

 

[TheAutumnWind]

You can pull obd1 codes with a paper clip or an aldl cable and a laptop

 

[CWARE]

I’m familiar with the method of pulling an OBD1 code using the paper clip or code key but will there be a code to read if the actual check engine light isn’t on?


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[TheAutumnWind]

Is your abs rear wheel only?

 

[TheAutumnWind]

I don't recall if a '95 just has rear anti lock or 4 wheel anti lock. If it's rear wheel only, dollars to pesos says it's the RWAL sensor. It's mounted on top of the diff, held on by one bolt, and has a tendency to stick/break off. If it's 4 wheel, then you REALLY need to pull codes as there are three wheel speed sensors to contend with, as well as the ABS unit itself.

 

[TheAutumnWind]

I’m familiar with the method of pulling an OBD1 code using the paper clip or code key but will there be a code to read if the actual check engine light isn’t on?


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You can try unplugging the abs box for a day or so and see if it resets. Or just delete ABS altogether which alot of people do on the Rear wheel only abs trucks.

If you have an abs light there is likely an abs code. WHy would you need to "check engine" if there is nothing wrong with the engine?

OBD-I ABS codes:
Code 21: right front speed sensor or circuit open
Code 22: missing right front speed signal
Code 23: erratic right front speed signal
Code 25: left front speed sensor or circuit open
Code 26: missing left front speed signal
Code 27: erratic left front speed signal
Code 29: simultaneous drop out of front speed sensors
Code 35: vehicle speed sensor or open circuit
Code 36: missing vehicle speed sensor signal
Code 37: erratic vehicle speed sensor signal
Code 38: wheel speed error
Codes 41 through 54: control valves
Codes 61 through 63: reset switches
Codes 65 & 66: open or shorted pump motor relay
Code 67: open motor circuit or shorted BPMV output
Code 68: locked motor or shorted motor circuit
Codes 71 through 74: memory errors
Code 81: brake switch circuit shorted or open
Code 86: shorted abs indicator lamp
Code 87: shorted brake warning lamp

 

[Big Mama]

What Chris said ^^ look for the abs code. His list it a good one to do visuals or check connections

 

[CWARE]

Ok. I’ll try to get the code it’s throwing. I did try unplugging the ABS Controller for about a day or so and upon start up with everything still unplugged the ABS light wasn’t on. The AC still didn’t blow at all though. Still not sure if there is a connection between the two or not but it sure seems so.


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[TheAutumnWind]

Ok. I’ll try to get the code it’s throwing. I did try unplugging the ABS Controller for about a day or so and upon start up with everything still unplugged the ABS light wasn’t on. The AC still didn’t blow at all though. Still not sure if there is a connection between the two or not but it sure seems so.


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Doubt there is any connection

 

[CWARE]

Did more troubleshooting on the Tahoe and still no luck. I checked the two ac related relays (under the hood and behind the dash) and both appeared to be good. I used a test light on the ac control module harness and it indicated there was power coming out of the harness into the module on the plug with 8 prongs. I’m assuming that’s how it should be.

I’m wondering now if there is a bag ground somewhere. I know it was stated that the ABS light and ac issue likely aren’t related but is there a possibility a ground somewhere is presenting the issue. Maybe a ground that grounds both the module and something ABS related? I’m not sure where else to go. I supposed I still need to attempt to get the OBD1 scanned for an exact abs Code.


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[TheAutumnWind]

Did more troubleshooting on the Tahoe and still no luck. I checked the two ac related relays (under the hood and behind the dash) and both appeared to be good. I used a test light on the ac control module harness and it indicated there was power coming out of the harness into the module on the plug with 8 prongs. I’m assuming that’s how it should be.

I’m wondering now if there is a bag ground somewhere. I know it was stated that the ABS light and ac issue likely aren’t related but is there a possibility a ground somewhere is presenting the issue. Maybe a ground that grounds both the module and something ABS related? I’m not sure where else to go. I supposed I still need to attempt to get the OBD1 scanned for an exact abs Code.


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Definitely should check your grounds. The one behind the block to the firewall often gets missed, and the one from the battery to the fender well area is just a sheetmetal screw and could come loose.

 

[CWARE]

Definitely should check your grounds. The one behind the block to the firewall often gets missed, and the one from the battery to the fender well area is just a sheetmetal screw and could come loose.

I checked the one from the battery to fender and it was fine. I located 2 on the firewall near the passenger side. One was up high and went into the harness for the underwood light. It was nice and tight and corrosion free. The one down lower underneath the area of the ac accumulator was removed and cleaned. The 3rd one was on the top of the passenger side frame section next to the motor. It appeared to have 2 ground straps connected to it. One went up to the ground mentioned earlier beneath the accumulator and the other went up into a harness that appeared to run up behind the motor. The ground point on the frame was extremely corroded. I took it all apartment and cleaned the screw and connections up. Put them back together and still nothing with the AC. The ground was getting a good connection as I tested it with a test light. The light came on when it hadn’t before.

Does anyone have a schematic showing all of the grounds on the vehicle?


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[east302]

There is another ground (at least on the 96+) near the bottom of the harmonic balancer. I’d guess that the TBI had the same one.

On a 98, the ABS (different system I believe than the 95) and a/c panel look to share G105 which is the one by the harmonic balancer.

Back to the a/c controller, do the vent controls work (the air doors adjust)? Watch the one by the gas pedal since it’s easier to observe.

The blower has two wires connected to it. With fan selected on high, check for 12V at the blower wire using a chassis ground and then using the ground wire that connects to the blower.

Just for kicks, here are the diagnostics for an inoperable blower on a 98. Refer to wiring diagram above. The connector (or something at the panel) is different for a 95, but maybe it will help.

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[CWARE]

There is another ground (at least on the 96+) near the bottom of the harmonic balancer. I’d guess that the TBI had the same one.

On a 98, the ABS (different system I believe than the 95) and a/c panel look to share G105 which is the one by the harmonic balancer.

Back to the a/c controller, do the vent controls work (the air doors adjust)? Watch the one by the gas pedal since it’s easier to observe.

The blower has two wires connected to it. With fan selected on high, check for 12V at the blower wire using a chassis ground and then using the ground wire that connects to the blower.

Just for kicks, here are the diagnostics for an inoperable blower on a 98. Refer to wiring diagram above. The connector (or something at the panel) is different for a 95, but maybe it will help.

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I looked for that ground near the balancer and did not locate one on my 95. I did locate the destination for one of the ground straps I mentioned before on the top of the passenger side frame rail next to the motor. It appears one of the straps goes to the back of the motor near the passenger side head/block. The bolt this strap is attached to is caked in oil but it seems almost impossible to reach on first glance. I’ll be attempting to deal with this now and see what happens.

I know that the blower motor works. I connected it to 12v and it fired right up. While the blower was running, I looked at the HVAC module but didn’t see any lights on indicating it was receiving power. Now the purple wire that I believe is the power wire that attaches to the blower does not seem to be supplying any power whatsoever to the blower. I tested it for 12v at the plug and got nothing and also tested it above the plug( into the wire itself) and got no power there either. I tracked that purple wire away from the blower motor and determined it ran to the plug for the blower relay. I previously tested the relay and it seemed to test good.

I then went through and re-checked the related fuses and all are still good.... This thing is wearing me out. I hate wiring which makes all of this extra brutal. Lol.


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[east302]

The control panel supplies the relay (orange wire) in high and the resistor for other speeds. Do you have power upstream of the relay on the Orange or dark blue wires? Or any of the wires shown at connector C230?

Those wire colors are based on the 98 model diagram; I’d think it would be the same or pretty similar for a 95 but understand that there was something specific to the 95 that was not carried over to later models.

If you have power there, then the control panel blower switch should be fine (I would think). If no voltage there, then see if the control panel supply (brown wire, circuit 141 on diagram below) is getting power. It is grounded to G200, which is on the crossbar above your knee, roughly above the parking brake.

Is this a new panel? I had a Dorman one that started smoking within a few minutes of installation. If *nothing* works on the panel but you have power to it, then it may be a bum part.






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[CWARE]

The control panel supplies the relay (orange wire) in high and the resistor for other speeds. Do you have power upstream of the relay on the Orange or dark blue wires? Or any of the wires shown at connector C230?

Those wire colors are based on the 98 model diagram; I’d think it would be the same or pretty similar for a 95 but understand that there was something specific to the 95 that was not carried over to later models.

If you have power there, then the control panel blower switch should be fine (I would think). If no voltage there, then see if the control panel supply (brown wire, circuit 141 on diagram below) is getting power. It is grounded to G200, which is on the crossbar above your knee, roughly above the parking brake.

Is this a new panel? I had a Dorman one that started smoking within a few minutes of installation. If *nothing* works on the panel but you have power to it, then it may be a bum part.


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I do have power on the orange wire at the harness that plugs into the ac module (connector C230).

I attempted to see if there was power at circuit 141 which I believe is the fuse box in the door jamb. I tried using my voltmeter on the connector for fuse 12 (ac fuse) but couldn’t really get a reading. I’m assuming it should be getting 12v’s with the key in the “ON” position. I did see the brown wire coming from the rear of the fuse block but couldn’t follow it.

I looked underneath the dash and found the ground for G200 and it looks fine. I can’t see any visible corrosion and it appeared very tight. The wires coming off of it were both black and I couldn’t trace them back very far as it was so tight under there. It may be beneficial to unbolt the fuse block and try to get a better look at the back of it


And yes the module is a brand new one. I initially resolved it back in March of this year and I assumed it was bad. Bought the new one and installed it and the ac worked fine. When it stopped working a few weeks ago I got a warrant replacement module as I assumed the new part may have been bad. Clearly it wasn’t the issue now and may have not been the issue in March either. I replaced the blower motor and resistor at the same time.


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