ABS Light...

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

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......

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

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.

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

Thanks!
mptc

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

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

Thanks again!

mptc

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

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

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

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

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?

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

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.....

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

I checked for power to the clutch harness...nothing. I traced back to the relay and there is power to the relay. I checked the relay again and it is operational. So there must be a short somewhere between the relay and the clutch? I did notice a fusible link between the relay and clutch although the wiring diagram does not indicate it. Is there a way to by-pass the wiring and go straight from the relay to the clutch to test if the clutch engages or not?

mptc

You have power to the relay, but is the relay being commanded on? When you have someone turn the A/C on with the car running, do you feel/hear the relay click? If the relay is ok, the PCM is not grounding it...

The only way to check this out is with a scan tool.......you have a pressure sensor code...clear it.....does it come back when you command the A/C on?

With a scan tool, you have to look at the data from the pressure sensor.....since gages said you had 90psi, then the sensor should be reading the same pressure....if it is reading too high or too low, the PCM will not command the compressor on.....

Also there is another input to the PCM....that is A/C request.....if the PCM does not receive a request from the HVAC head, it will not command the compressor on....need to see this on the scan tool.....

You can disconnect the PCM and jumper the A/C relay circuit to ground(no key in the ignition, disconnect battery, then disconnect all the harnesses to the PCM.....reconnect battery......turn key to on....now jumper the relay circuit to ground....you will need a wiring diagram to know which line to jumper.....) but all that will do is validate the clutch circuit, if the clutch clicks, my money is on the sensor, and you need a scan tool to validate this.....

You have power to the relay, but is the relay being commanded on? When you have someone turn the A/C on with the car running, do you feel/hear the relay click? If the relay is ok, the PCM is not grounding it... Okay...did not hear or feel a click.

The only way to check this out is with a scan tool.......you have a pressure sensor code...clear it.....does it come back when you command the A/C on?

With a scan tool, you have to look at the data from the pressure sensor.....since gages said you had 90psi, then the sensor should be reading the same pressure....if it is reading too high or too low, the PCM will not command the compressor on.....

Also there is another input to the PCM....that is A/C request.....if the PCM does not receive a request from the HVAC head, it will not command the compressor on....need to see this on the scan tool.....

You can disconnect the PCM and jumper the A/C relay circuit to ground(no key in the ignition, disconnect battery, then disconnect all the harnesses to the PCM.....reconnect battery......turn key to on....now jumper the relay circuit to ground....you will need a wiring diagram to know which line to jumper.....) but all that will do is validate the clutch circuit, if the clutch clicks, my money is on the sensor, and you need a scan tool to validate this.....When jumping the A/C (C2) relay to ground I heard an audible click and felt it as well. I even took the relay off the bracket and held it in my hand to make sure it was the one clicking.

According to Chilton I have high and low pressure cut off switches. According to the wire diagram I have an A/C pressure sensor only. The wiring diagram matches what I am seeing. Is it necessary to verify that it is the pressure sensor or have we narrowed it down by deduction to that. Or am I getting ahead of myself? Is there another possible explanation (other than a short between the relay and compressor). Can it be changed without discharging the system?

Thanks!

mptc

One clarification on the information above...the click I heard and felt was the relay only. I did not hear or feel a click in the clutch itself. I had the A/C control in both normal and max position in addition to the off position.

mptc

As I said in post #17, if you want to check the ENTIRE relay circuit, you have to diconnect the PCM(with battery disconnected first).....then reconnect battery......with the key on(engine not running), then you need a wiring diagram to know which circuuit in one of the harnesses is the ground control for the Compressor relay......if you ground that circuit, the relay clicks, and the compressor clutch should click as it is pulled in....If that happens, you know the ENTIRE CIRCUIT IS OK.....Then you are dealing with a possible sensor problem, that can only be verified wioth a scan tool....if the relay clicks, but the clutch does not, then you check for power at the harness of the clutch for power and ground with a test light...

In some cases, if an A/C code is set, it may have to be cleared before the A/C system can operate......if you have an A/C code, clear it, then operate the system, it doesn't run, and the code comes back, then the sensor will have to be checked with a scan tool......

As I said in post #17, if you want to check the ENTIRE relay circuit, you have to diconnect the PCM(with battery disconnected first).....then reconnect battery......with the key on(engine not running), then you need a wiring diagram to know which circuuit in one of the harnesses is the ground control for the Compressor relay......if you ground that circuit, the relay clicks, and the compressor clutch should click as it is pulled in....If that happens, you know the ENTIRE CIRCUIT IS OK.....Then you are dealing with a possible sensor problem, that can only be verified wioth a scan tool....if the relay clicks, but the clutch does not, then you check for power at the harness of the clutch for power and ground with a test light... As I mentioned in post #16 I did check power to the harness with a test light. There was nothing. I checked power to the relay and there is power there. And I did check the entire circuit by disconnecting the PCM...post #18. The relay clicked but the clutch did not.

In some cases, if an A/C code is set, it may have to be cleared before the A/C system can operate......if you have an A/C code, clear it, then operate the system, it doesn't run, and the code comes back, then the sensor will have to be checked with a scan tool......

Now here is the interesting part. I wanted to check if the wiring from the relay to the harness plug was good or bad. I started the engine and turned the A/C on and stuck the point of my tester into the power (green) wire just below the relay at different spots. Nothing. So I turned off the engine (disconnected the battery) and about an inch below the relay I stripped the green coating from the power wire that leads to the compressor. I reconnected the battery, started the engine and the A/C and I jumped the power (green) wire to the battery (pos.) and the compressor clutch engaged and ran. I let the engine run for 5 minutes. It did not put out any cold air but the clutch was engaged and running the whole time. So this verifies that the power (green) wiring from just below the relay to the compressor is good.

So in summary....I have 1) power to the relay. 2) The relay itself is functioning. 3) from the PCM harness to the relay is good because it engages (clicks) the relay when jumped to ground. 4) the power (green) wire is good from just below the relay to the compressor because when jumped to the battery the compressor clutch engages.

So why when I did the test from the PCM harness did the relay click but the compressor clutch did not? Could there be a problem not with the relay but with the base that the relay plugs into?

Again thank you for your imput!

mptc

Do an ohm check between the green wire and the contact in the base that goes to it....if "OL" you found your problem.....if it reads zero, even though the relay clicks, did you try another relay?

You say you checked for power to the relay....was there power on two legs?

Do an ohm check between the green wire and the contact in the base that goes to it....if "OL" you found your problem.....if it reads zero, even though the relay clicks, did you try another relay? I will check this.

You say you checked for power to the relay....was there power on two legs?Yes there was power on two legs.


Thanks!
mptc

Okay I think I discovered the problem(s). First of all...I did an ohm check and it was fine (no problem there). To verify, I removed the relay and jumped from the battery to the contact on the base where the green wire goes and it engaged the compressor clutch. So the relay, the base and the harness are all good. Now for the other problem that I discovered. When jumping from the battery to the contact (green wire) the clutch did not engage at first. I reached down and discovered some play in the harness when it is plugged into the compressor. I moved it to the right and the clutch engaged. I moved it left and it quit. This is not alot of movement but enough to start and stop the clutch. This is probably why the clutch did not click when I jumped the PCM harness wire to ground (post #19). So I agree with you that the pressure sensor is the ultimate culprit. If it is faulty this does keep the power from going to the compressor harness, correct?

Thanks!
mptc

If the pressure data from the sensor is too high or too low, the PCM will not ground the relay, to power the clutch.....

Unfortunately, the only way to know for sure, is with a scan tool...A/C codes must be cleared and data from the sensor must equal the pressure readings from the gages....AND an A/C request must be present....

As for your clutch contact...it's either the contacts in the harness(are they tight enough?) or a bad contact in the clutch itself.....

If the pressure data from the sensor is too high or low then the sensor is malfunctioning. Have all other possibilities been eliminated? Is so, then is it necessary to determine how it is malfunctioning? Why not just replace the sensor?

Thanks!
mptc

You could do that....and it still might not work.......What if the sensing line is an open circuit?

But since you don't have access to a scan tool, it might be your best guess....

You could do that....and it still might not work.......What if the sensing line is an open circuit?

But since you don't have access to a scan tool, it might be your best guess....

Is it possible to measure voltage in the sensing line with the key turned on and the A/C turned on to verify power is going to the sensor?

Thanks!
mptc

Same car expanded problem.

First of all I will let you know how the A/C pressure sensor problem works out shortly. The part will be in this week.

Secondly, the ABS problem has morphed or expanded into a new problem. The car is blowing the 10 amp fuse for (electric fan/starter and generator/seq. fuel inj.V-6/cruise control/anti lock brakes) as fast as I put them in. It started slowly and now the fuse blows when I turn the key to on without starting. It has a significant loss of power/performance when this happens.

I tested the brown wire leading out of the fuse all the way to the generator and there is continuity. I found a main ground (one of three grounded to the engine block) that had the coating chewed by rodents. So I cleaned off the exposed wire and wrapped it in several layers of electrical tape as well as the plastic casing. It still blew the fuse.

Help!

mptc