['02 MGM LS] Air suspension diagnostics?

[SpitShine_PL]

Lemme clarify:
I started out by hooking up brand-new spring solenoid valves and the replacement height sensor (from a wrecked '99 TC). The Check Air Suspension (CAS) light came on after five flashes and a beep. It would come on exactly the same with the air suspension switch on or off, having opened and shut all the doors, with the car on the ground or on a column lift. (The car was lifted by the frame, not the wheels.)

I left the replacement sensor and the new solenoid valves installed in the car and left the garage with the column lift and went home to read up on the diagnostic procedure in the 00-04 FSM and Dereck's writeup.
The CAS light comes on consistently, the air suspension switch on or off, in every condition the air suspension module would determine OK to vent or pump the air springs -- which I won't install did not install before this problem is sorted out.

I'm planning to start the diagnostics on Friday and continue through the weekend.

I still don't know if 20 ohms instead of 10 ohms are correct with every other reading OK.

[jaywish]

Thanks for the clarification. I was cornfused.

Not being an engineer I don't know why Ford requires 3.3 volts for this test.

[SpitShine_PL]

That is what was specified by Dereck in the link above on the LincolnsOnline forum. I might ask why this specific value, but it might have something to do with the ride height sensor being a Hall sensor device.

[jaywish]

That is logical.
I guess it would then alter the resistance.

I find the expected sensor test results a bit puzzling. I will look at it more.

[gadget73]

OL is greater than 1 megohm so no issue there.

guessing the power supply to the thing is 3.3v then. Could verify that just in case, but I doubt it really matters. Once its got enough voltage to function the hall sensor becomes a simple on/off switch. If it reads 20 ohms, I'm guessing it has some internal resistor that is adding to the switch function.

[SpitShine_PL]

Well, Dereck's writeup says the ride height sensor should be driven with 3.3V during the bench ohm-out. I do not know why said 3.3V specifically.

It's either a specifically test-bench voltage value, or the air suspension control module indeed steps down from +12 V and outputs 3.3V to the positive input on the height sensor; the height sensor receives input voltage via circuit 418 (control module to air suspension switch (in the trunk), followed by circuit 429 (air suspension switch to height sensor (+) input).
This indeed will be verified with the diag procedure from the FSM, it includes voltage and ohm testing of circuit 429.

[SpitShine_PL]

UPDATE:

The weekend was semi-successful with the air suspension diagnostics.
The vent valve is dead (the diode on the coil and the winding are). Ordered a new compressor from Arnott; the old one had the dryer replaced some time ago, that's why I thought it was OK before I yanked the whole thing out; then I found out that the compressor cylinder casing started to rot, so I decided to relegate it to trash.

While I didn't begin deep testing the circuits (continuity and volts), I found something funky already.

I popped the glove box tray wide open and found the air suspension module resting on that white corrugated tube under the dash. Well, when you see a factory module not in its bracket, you know someone's been playing with it.

Connector C2131b, grey/black wire (circuit 679), goes from the suspension control module to the vehicle speed sensor. What do I find here? 2 inches from the connector, there's an ugly splice made into the GY/BK wire. The splice wire lives in that floppy, black protective sleeve and comes off the GY/BK wire toward the radio. I tugged that splice wire gently and something rattled behind the dash close to the driver's footwell panel. Definitely not factory.

The wiring diagram says there should be no splice into the GY/BK wire #679 this close to the suspension control module.

"WE NEED TO GO DEEPER. DEEPER UNDER THE DASH!"

[sly]

Looks like you're in for a lot of detective work.

[SpitShine_PL]

Yup, but I'm in luck: got the whole FSM diagnostic procedure on hand. I don't have the Super Star II scanner for the air suspension, but from what I garner from there and the wiring diagrams, the 'non-functional' tests (the ground work with a multimeter and a test light, opposed to the 'functional' tests triggered in the control module by SSII) are basically the troubleshooting steps taken when a SS II test fails or there is a DTC returned by the tester / air suspension control module. They should tell me exactly what is wrong, and along which circuit / wire to look.

[86VickyLX]

I will say that the vss input is used for the variable steering assist. It goes to the radio for speed sensitive volume. It also comes through the drivers side firewall from the ecm harness and also for the cruise control servo assembly under the hood.

[SpitShine_PL]

I dug into the dash.

The mystery splice off connector C2131b, grey/black wire (circuit 679) followed across the dash and down pillar A. It joined a harness that was not in the cable ducting along the door jambs... I traced the whole wire back to the trunk, where it was spliced into a defunct connector, a leftover from a cellphone hands-free set (I also found an antenna cable left from the hands-free set).

The good thing is that I found no more funky splices. The suspicion is that there still might be a broken or short line in the RAS wiring; the worst case scenario is a dead air suspension control module.

Will continue FSM diagnostic tests today.

[SpitShine_PL]

More updates:

On with the RAS diagnostic procedure.
I already pinpointed several problems:
Circuit 57, suspension module harness pin 6 (wired to the steering position / angle sensor) has 80 ohms instead of < 5 ohms. LOL.
Circuit 419, suspension module harness pin 11 (goes to the Check Air Suspension warning light on the digi dash) reads 6.5 volts instead of > 10 volts.
Circuit 419, air suspension test connector pin 4 (spliced to suspension module harness pin 11), reads 0.1 millivolt instead of > 10 volts.
(So there is a problem in circuit 419.)
Circuit 432, air suspension test connector pin 2 (ground wire, spliced to the ground wire from the ride height sensor and spliced to the circuit 432 leg going to suspension module harness pin 8), reads 11 volts instead of 0 volts.

Will have to look for splices and test some more.
I'm also waiting for a replacement air suspension control module; since I got no SS II on hand, I'm hitting a wall without a replacement module to confirm the results.

[SpitShine_PL]

UPDATE:

Getting there, but slowly (no time on my hands until next week, gah!).
I'm gonna run FSM diagnostics on the EVO/steering angle sensor connections, since circuit 57 is affected. Gonna keep you posted.

[SpitShine_PL]

OK, UPDATE:
Finally got some free time to continue the diagnostics:

Hooked up a new compressor and a known working RAS control module. Nada, got the CAS warning light again. This is definitely a wiring or steering angle sensor issue. Need to check out the VSS (vehicle speed sensor) connection and performance, too; although I know the EVO (VAPS) works, the steering gets stiffer at highway speeds. Gonna test out the VSS, the steering angle sensor and the defective wiring circuit today and tomorrow.
Making longer strides here, finally.

[SpitShine_PL]

UPDATE, DAY 2:
With the new compressor and a known working RAS module, I installed both (brand new) air spring solenoid valves.
Now I lost voltage at air suspension control module harness-side pins 1 and 15, which should be hot all times; pin 16 on the same harness is hot with the ignition key on (as it should).
The BJB (battery J-box) fuse # 8 (30 amps) feeds pins 1 and 15 and should be hot all times, +12 V. It is not. The suspension relay is OK (tested), its wiring side has proper voltage on the correct pins.

I'm starting to lose my mind here.