ELC compressor not coming on - tests good

[rmorton]

I'm still chasing my problem with the air ride. The compressor will not come on automatically nor manually with key on and pressing trunk button. I put 12 volts to the compressor this morning and it runs fine. I swapped out the 30amp fuse and the relay with known good ones. Still no luck.

This code comes up with the tech 2: "C0660 Level Control Exhaust Valve Circuit Malfunction". So I'm assuming that has something to do with the problem. But I can't find any info on this exhaust valve for the air ride. Has anybody come across this code or does anybody know how to diagnose the exhaust valve circuit?

[agrazela]

Exhaust valve gets plugged with grit and debris. When exhaust valve no longer works, the compressor will not come on (I assume some BCM logic based on the existence of the code you pulled). This eventually happens to approximately 100% of these compressors.

GM decided for 2000+ models--probably to save themselves a thousandth of a penny per vehicle--to make the exhaust valve no longer a serviceable / separately replaceable part. Instead you are supposed to replace the entire compre$$or.

I believe I have read of people taking the compressor apart and cleaning it up / lubing it / blowing out the exhaust valve. I decided to just bypass mine with a $13 Monroe AK29 manual inflation kit; 35psi normally, 40psi when towing a small utility trailer or loading up the trunk for a road trip.

EDIT: Did not answer your question I know, but does provide an alternative solution!

[ddalder]

The Rear Integration Module (RIM) controls the exhaust valve on the compressor assembly. If it detects a fault in the circuit (open, short to ground, short to 12V) it will set a code. I'll have to look up that code a little later to give you the exact specifics. It could be a defective solenoid, wiring problem or possibly even the RIM. My bet would be one of the first two.

[rmorton]

agrazela - Yep, I did the same "fix" on the 98 bonnie and on the wife's Montana. I just hate to give up on this one since the compressor seems to be ok.

ddalder - If you have any further specifics on that code, I would love to have it. Where are you looking it up? I've surfed the web, but not finding much. I'm suspicious of the wiring since I can't clear the code. If it were the solenoid, I would think that the code would clear until the next time solenoid failed.

[ddalder]

As per the service manual...

In order to reduce current draw during air compressor starting, the RIM (Rear Integration Module) performs an air compressor head relief sequence before air compressor operation. This sequence reduces the air pressure in the air compressor cylinder during start-up. The air compressor head relief sequence occurs as follows:

• Exhaust solenoid is energized.
• Air compressor is activated 1.3 seconds after the exhaust solenoid is energized.
• Exhaust solenoid is de-energized 0.5 seconds after the air compressor is activated.

Therefore...

Since the air compressor engages briefly with every ignition cycle, the exhaust solenoid is ultimately activated during every ignition cycle as part of the "Air Compressor Head Relief Sequence" outlined above. This will of course also occur any other time the compressor is commanded on. This is undoubtedly why you can't ever seem to clear the code.

As for the DTC...

C0660 - Level Control Exhaust Valve Circuit Malfunction.

When this DTC is set, it's because the exhaust valve solenoid output is found to be open or shorted to ground for ten seconds. When this occurs, the ALC system will be inoperative.

[rmorton]

Got it. That makes sense. Thank you for that info!! So probably wiring?

The system was working fine before I replaced the rear shocks. In fact, it was running far too often due to the old leaky shocks so I pulled the relay out until I could get new shocks on. After new shocks, I put the relay back in...nothing.

Could the solenoid be seized up and cause this circuit fault? The manual doesn't happen to show which wire energizes the exhaust solenoid does it? There are 4 wires on the compressor connector. The black appears to be ground and the green appears to be power for the compressor. There are 2 others. I assume the exhaust solenoid would share ground with the compressor?

I'm thinking I could put power to the solenoid and listen for a click? Or test for power on the solenoid wire when the ignition is turned on...

[ddalder]

Double check the fuse for this circuit (it will be a 30A). Try swapping the relay with one that is known to be good. Lastly, I would inspect the connector and wiring carefully for any corrosion or breaks. It seems coincidental in regards to when this stopped working, but these are still valid checks to carry out first. I know this sounds silly, but make sure the relay was put back in the correct socket given there are a few spare relay positions in the fuse block. Post back what you find.

The wire colours are:

Red - Battery Positive Voltage (To The Exhaust Solenoid Only)
Dark Green - ALC Compressor Motor Control
White - ALC Exhaust Solenoid Control
Black - Ground

The control system for the exhaust solenoid works opposite to what most people may think. There is always battery positive voltage on one side of the solenoid coil by way of the RED wire. To engage the solenoid, the RIM grounds the other side of the coil through the WHITE wire to complete the circuit. The DARK GREEN wire supplies battery positive voltage to the compressor motor, but only when the motor control relay is activated so it will not always show power with a meter or test lamp. The BLACK wire provides a ground only to the compressor motor (remember that the ground for the solenoid is provided by the RIM through the WHITE wire).

I do not recommend trying to probe wires by poking through the insulation, especially on the exterior of the vehicle. I've repaired far too many faults for people that did (or had this done) to their vehicle. It may only be a small hole but left unsealed, moisture will get in and corrode the wire over time.

[rmorton]

Wow, ok. Yeah I'm very grateful you explained that. I was thinking wrong about the wiring. Thank you very much for looking this up and getting it to me. I will post what I find out.

I have checked and rechecked the 30amp fuse as well as the relay. I've swapped both with known good ones.

[rmorton]

Ok, tested the red and white wires with ignition off - nothing. Had wife turn ignition on - within a few seconds the red and white had 12 volts for a second or so and then back to nothing just like you said. The black and green never got voltage. So I would conclude that the wiring is ok and the solenoid is the problem. Think Im on the right track?

[ddalder]

Was the connector for the compressor still plugged in when you tested? If the circuit was connected and you didn't hear a click then I'm thinking it's likely the solenoid. What you can try is to unplug the compressor and apply 12VDC across the red and white wires. Make sure you have a fuse inline with the supply voltage though for protection. I would probably fuse it at 10A. If there is no activity from the solenoid then that's your answer. You can also try measuring across the red and white wires as well with an ohm meter. If it's a dead short or open that will also answer this for you. I would guess (not having measured one personally) that you should likely see a few ohms of resistance across the coil.

[rmorton]

I unplugged the harness and put 12V to the red and grounded the white (actually both wires are white on the compressor side of the connector, but I made sure I was applying 12V to the right one). No click and none of the air let out of the shocks. I measured resistance across the red and white and got .9 M ohms. Resistance was .9 M ohms across the red and black. 15 M ohms from white to black.

That's too much resistance across the red and white right?

[ddalder]

That sounds excessively high to me. I've never measured mine, but for a solenoid coil, that doesn't sound right. The fact that you also applied 12V and had no result makes me believe that's your problem.

[96 SSEi]

if its an easy swap for the emergency pump, I woild put a decent one in so you can inflate tires from the trunk

[rmorton]

I can't really tell how hard it is to get out of there. Somebody said you have to remove the bumper cover. I guess that's my next step.

[Luxrain]

I can't really tell how hard it is to get out of there. Somebody said you have to remove the bumper cover. I guess that's my next step.

ive done it w/out removing the bumper cover but it makes life easier. also the whole cover doesnt need to be removed and make sure to use alot of penetrating oil on those bolts for the compressor

[96 SSEi]

hello, found this - not same car- denali 2000- but same thing:

It sounds that you have a wiring issue.
There are two wires that go to the exhaust solenoid. The Orange wire is +12V power coming from the 30A RTD fuse and the Dark Blue wire is control circuit from the Suspension Control Module ( the module provides ground to the solenoid it order to operate it). I am almost sure you have a problem with the Orange wire.
Use a test light connected to ground and check for power on the Orange wire at the compressor connector.
If you do not get power, check the RTD Fuse in the underhood fuse block.
If the fuse is OK, then trace this orange wire down till you find an open circuit ( break/corroded wire).
I am almost sure you will find a promlem in the wiring harness running under the vehicle in right rear corner ( where the C450 connector is, see the picture below).

...http://www.justanswer.com/chevy/36ydc-g ... fault.html

[ddalder]

hello, found this - not same car- denali 2000- but same thing:

It sounds that you have a wiring issue.
There are two wires that go to the exhaust solenoid. The Orange wire is +12V power coming from the 30A RTD fuse and the Dark Blue wire is control circuit from the Suspension Control Module ( the module provides ground to the solenoid it order to operate it). I am almost sure you have a problem with the Orange wire.
Use a test light connected to ground and check for power on the Orange wire at the compressor connector.
If you do not get power, check the RTD Fuse in the underhood fuse block.
If the fuse is OK, then trace this orange wire down till you find an open circuit ( break/corroded wire).
I am almost sure you will find a promlem in the wiring harness running under the vehicle in right rear corner ( where the C450 connector is, see the picture below).

...http://www.justanswer.com/chevy/36ydc-g ... fault.html

The wire colours, connector reference and schematic here don't match the Bonneville and the compressor assembly is not the same as our cars. He has already disconnected the compressor at the connector under the rear of the car where it plugs into the main body harness. When he applied 12V to the wires that activate the exhaust solenoid there was no activity. There was appropriate voltage from the RIM to the exhaust solenoid when he measured that circuit so the body harness wiring is not the problem. It is possible that there is a wiring problem within the compressor assembly, but I strongly suspect it is much more likely the solenoid is faulty, probably due to corrosion from water intrusion over time.