ABS Light...

[mptc]

I have a 1995 Oldsmobile Cutlass Ciera 3.1L V-6. I am trying to troubleshoot why the fan and AC compressor are not operating. I checked for wiring shorts etc. I pulled the ECMs to look for a possibe blown fuse (that some models contain)(I did disconnect the neg battery terminal before doing this). No such luck just computer components. I put the ECMs back in place rechecked the harnesses that plugged into the modules and started the car. It started fine but I noticed a slight ozone (electrical) smell and the ABS Light on the dash is now staying lit. It is not flashing. According the the owners manual I have brakes just not anti lock brakes. I took it for a spin around the block and the brakes work...I pushed them hard several times.

Are the two incidents related or was it coincidence. What do I look for to troubleshoot the ABS system. Any help related to the original problem would be helpful too. Is it driveable?

Any help would be greatly appreciated!

mptc

[Tech II]

So, the ABS light was not on before messing with the modules?

Unfortunately, the year of your car is a problem........by that I mean, it was a transition year between OBD I and OBD II......you need to read ECM and ABS codes......most of the code readers and scan tools out there, can't seem to read these codes, for this year.....it takes either expensive equiptment or GM scanners to do this.....

If the ABS light is on, a code is set, and needs to be read.......

As for the A/C system a code could be set in the ECM, which disables the A/C system.......this could be a low charge code......if you are low on freon and this system uses a pressure sensor, then if pressure is below 45 psi, then the compressor won't engage and the cooling fan won't run because there is no compressor running......

[mptc]

First of all no, the light was NOT on before messing with the modules.

Second I have the ABS code...14 which indicates "Enable relay circuit open". The possible causes are 1) bad ground 2) bad enable relay 3) abs hydraulic unit defective.

Are any of these D-I-Y type repairs?

mptc

[gmtech1]

The relay is part of the unit. Can be a DIY repair, but can also be tough to bleed the brakes after the repair is done.

[mptc]

My Chilton book is useless regarding the abs...where is the relay located?

Thanks!
mptc

[gmtech1]

Its internal to the abs unit, its not serviced seperatly.

[mptc]

Okay, the ABS unit is not shown in my Chilton Book. Is it near the ECM or part of it?

Thanks again!

mptc

[maxwedge]

Should be near the master cyl., lots of lines connected to it.

[mptc]

Okay I located the ABS Relay...it is separate from the master cylinder and attached to the firewall (passenger side). Using a multimeter is there a way to verify that the relay is faulty?

Thanks!
mptc

[mptc]

Okay...additional information. I tested the ABS relay (as well as others including the compressor switch relay) and they are all okay and fully functional.

That leaves (unless there is another relay associated with the ABS) #1 bad ground, and #3 hydraulic unit defective. Any direction about locating a bad ground? Where is a logical place to start? Any idea how to test the hydraulic unit or where to look for problems?

Thanks!

mptc

[mptc]

More info....regarding my original post...I stated that I was troubleshooting why the fan and AC compressor clutch were not working. I disconnected the wiring from the engine coolant temp. (ETC) sensor and low and behold the fan started running. It ran until I plugged the connector back into the engine coolant temp sensor. Is this an indicator that the ETC sensor is bad?

Thanks!

mptc

[Tech II]

You set a code by disconnecting the sensor......this caused the PCM to command the coolant fan on....so you know the circuit to the fan(via the relay) from the PCM is ok.......

As I said before, if you have the vehicle running, and command the A/C on, and the compressor does not engage, that coolant fan may not come on if a pressure sensor is one of the inputs to the PCM.....for example, when the pressure in the system reaches a certain point, then the PCM commands the fan on......if the compressor does not engage, then the fan won't run....

Have you checked for PCM codes? Have you checked hi/lo pressures with a set of gages?

[mptc]

Okay...had the A/C system charged (addding 8 to 16 oz.) but the compressor did NOT turn on. So the amount of refrigerant and the pressure is not the problem. So I was told a few things to look for. First is a 10 amp in-line fuse that is supposedly to the left of the steering column taped to harness. I was told to test it...well I couldn't find it anywhere in or around the steering column. If the fuse was good I was told to test the red/blk wire going into the A/C pressure sensor (three wires red/blk, gray, and red). Well I turned the ignition to on and the a/c to max and there was no power going to the red/blk wire. I put the test light into the gray and it lit up. I tried the red and nothing. I tried to jump the red/blk and the red to see if the clutch would click and nothing. So if this fuse is in fact present (left of the steering column) it may be bad. What do I look for? The wiring diagram show a pink wire leading from the fuse. I am lost as to where to look.

Thanks!
mptc

[Tech II]

It's hard to help if you don't answer questions....

I asked if there were any PCM codes? i.e., P0532?

You added freon, but do you know what the pressures(hi/lo) are? Think you need a minimum of 50 psi....

If you are low on freon OR if there is a problem with the pressure sensor or data, that compressor is not going to engage OR if the compressor clutch is bad(did you check for power and ground at the clutch connector?)..........

The pressure sensor has 3 wires going to it.....THEY CAN NOT BE JUMPED! You could do that on the old pressure cycling switch(two wire switch), but not on this setup......

If you disconnect the harness, you have three wires.....Power(5 volts), Ground, and the signal circuit......If you jumper the power line to the signal circuit, the pressure signal is too high and the compressor won't run.....if you jumper the ground to the signal line, the pressure signal is too low and the compressor won't run.....you do not jumper the power to ground!

So, if the sensor is bad, you won't get the correct pressure signal to the PCM(way a shop checks this is they attach their scan tool to the car and the pressure reading on the scan tool should match the pressure reading on the gages attached to the system).....you also won't get a reading if the ground or signal wire is open to the PCM.....in some cases, even if you add freon, the compressor won't run if the code is present in the PCM....it may have to be cleared.....and like I said, you also have to check power and ground at the cluch harness.....

I just remembered one more possibility, the PCM needs a "request" from the HVAC control head, to command the compressor on.....once again, this can only be checked with a scan tool capable or reading this data, like a GM Tech II scan tool.....

[mptc]

Originally Posted by Tech II

It's hard to help if you don't answer questions....

I asked if there were any PCM codes? i.e., P0532? The only code was 1530 which is pressure sensor error. I don't know if that was because I unplugged the wires to test or not.

You added freon, but do you know what the pressures(hi/lo) are? Think you need a minimum of 50 psi.... The pressure got up to 90 psi and the compressor still did not turn on. So I don't think fluid levels or pressure is the problem.

If you are low on freon OR if there is a problem with the pressure sensor or data, that compressor is not going to engage OR if the compressor clutch is bad(did you check for power and ground at the clutch connector?)..........

The pressure sensor has 3 wires going to it.....THEY CAN NOT BE JUMPED! You could do that on the old pressure cycling switch(two wire switch), but not on this setup......This is good to know...thank you.

If you disconnect the harness, you have three wires.....Power(5 volts), Ground, and the signal circuit......If you jumper the power line to the signal circuit, the pressure signal is too high and the compressor won't run.....if you jumper the ground to the signal line, the pressure signal is too low and the compressor won't run.....you do not jumper the power to ground!

So, if the sensor is bad, you won't get the correct pressure signal to the PCM(way a shop checks this is they attach their scan tool to the car and the pressure reading on the scan tool should match the pressure reading on the gages attached to the system).....you also won't get a reading if the ground or signal wire is open to the PCM.....in some cases, even if you add freon, the compressor won't run if the code is present in the PCM....it may have to be cleared.....and like I said, you also have to check power and ground at the cluch harness.....I will do this.

I just remembered one more possibility, the PCM needs a "request" from the HVAC control head, to command the compressor on.....once again, this can only be checked with a scan tool capable or reading this data, like a GM Tech II scan tool.....

Thanks for the imput!

mptc