['02 MGM LS] Air suspension diagnostics?

[SpitShine_PL]

Hi all,

I'm restoring the air suspension on my 2002 GrandMa. I got the car with cop springs, someone got cheap on replacing the ride height sensor, dropped in the cop springs, disconnected the LH air spring solenoid connector and the compressor connector.

The old and non-functional ride height sensor was crusty and stuck (it took some effort to expand and collapse it), so I discarded it.

Before installing the air springs, I decided to test the air suspension system.

1. The Check Air Suspension warning light would come on steadily after a beep and flashing five times.

2. I hooked up the compressor connector, the electric connectors to two new solenoid valves (with the air lines still connected to the old solenoid valves).

I also installed and connected a used ride height sensor that Clay (thanks, dude!) sent me from a scrap yard in the states.
The old one is the bellows-style sliding sensor, P/N F8AZ-5359-AA.


My replacement is the same and has the same wire colors (red, dark green, black and dark blue) on the connector. The replacement was pulled from a Whale Town Car.

3. The air suspension trunk switch did not clear the Check Air Suspension light from the dash; the compressor didn't run despite the air suspension circuit was seemingly closed.

4. The compressor runs when I short its relay holder pins (30 to 86), so it's operational.
--------------
Conclusions and questions:
1. The replacement ride height sensor might be defective. I can 'bench-test' that once I get my regulated voltage power supply delivered.
2. The wiring diagram shows the pinout color assignment as follows:
SENSOR connector to HARNESS connector
RED to VIOLET/GREEN (power input)
DARK GREEN to ORANGE/BLACK (output to control module)
DARK BLUE to PINK/BLACK (output to control module)
BLACK to BLACK/PINK (GND)
Is it possible that the Town Car ride height sensor which the replacement for my car has a different pinout and the connection with the onboard wiring is mismatched?
3. The air suspension control module might be disconnected, but I doubt it - if it was, the Check Air Suspension light would be dead, right?
4. The wiring is broken or short at some point, so the circuit between the solenoid valves, the ride height sensor, the module and the compressor is not closed.
I want to test that. I found Dereck's writeup, but it's applicable to LTCs up to MY 1997 and I don't know if it's any good for a 2002 GrandMa:

http://www.lincolnsonline.com/tech/00061.html

I also got some air suspension wiring diagrams for the 1998-2002 Panthers:




Looking for people here to bounce ideas off this one. If I'm missing anything, lemme know, because the system is simple, but its testing will be tedious and I don't want to throw parts and money, especially that I don't live in the States; even a used ride height sensor for 100 bucks (part + delivery) would be an overkill if it's only a bad wire somewhere; not to speak of getting a whole compressor or control module.

[gadget73]

looks like if the module was unplugged you'd get no air suspension light, so I think you're right about it being plugged in.


possible the height sensor pinout is different. I don't think that thing changed much electrically since the 80s other than the plugs. F8 is a 1998 part number but that seems reasonable to find on a 2002 model.

[SpitShine_PL]

Thanks for the input.
I was thinking the same thing; I got the used ride height sensor complete with the onboard harness connector (cut off the remainder on a wrecked LTC). It will make it easier to identify if the pinout (and hence the wiring colours) is different.
I just hope that I didn't kill the replacement sensor; it has a power input, a GND line, and two trim signal outputs, so one of the two latter could have been connected to the +12 V input signal, and EEEEK!

[gadget73]

as I recall, it switches one or the other to +12v when its high or low. I have forced the air suspension to inflate before by reversing the two signal wires. I expect you could just jump one or the other to +12v too. With no sensor installed the system should think its at trim height so I don't think you'll get a fault for that. Might be worth ohm checking at the control module connector to verify that the solenoids read properly. Not sure what pins they are.

[SpitShine_PL]

That won't be problematic, just tedious. I got the correct wiring diagrams for MY 2002 and a big extract from the FSM diagnostic procedure. I wish I had the Super Star II tester on my hands, but a multitester must do.

[gadget73]

should be able to just jumper the diag plug and count the flashes on the warning light. Done it that way on a Mark VII at least. I've never owned a SuperStar 2.

[jaywish]

How did you do the test? With the height sensor in you hand?

[gadget73]

Its a hall effect sensor, basically a magnetic switch. Power it + and -, one output switches when low, one switches when high. I think both are off in the middle, but I might be wrong on that. Also can't recall if they switch + or -, but easy enough to work out with a meter. I know if you reverse the high and low output, the suspension behaves opposite how it should. I don't know if it actually has any ability to "see" the sensor being present or not. Would be worth confirming +12v at the air suspension computer when the switch in the trunk is turned on.

to make it spit out codes, ground the "diag input" pin in the self test connector. There is a ground wire in that connector too, so you can just jump them together. Turn the key on and it will blink out codes.

[86VickyLX]

I couldn't find any way to run a self test without some sort of scan tool connected. No documentation that supports it either. Everything mentions superstar tester or equivalent. it's possible that with a test light or an analog dash it might display codes. The digital dash's air suspension indicator does not flash every time the trigger wire is grounded. It is delayed through the board. There are 3 wires that are on the diag connector. Gray/red, black/pink and dark green/light green.
Dark green/light green is the ground output for the check suspension indicator. You're supposedly connecting the gray/red and black/pink to enter diagnostics. And with a test light hooked to 12v and grounded through the dark green/light green wire you in theory might get flash codes. But to electronically test anything you need a scanner unless someone has more information.

If the system is active, the light will be one for a few reasons. An open or shorted air spring solenoid, a bad height sensor, or the system being unable to reach trim height (by either raising or lowering the system) Pay close attention to when you first turn on the ignition. If you hear a click from the fender area, it is possible that the system is trying to vent air to lower it to spec. If you hear nothing, it's possible the system is seeing something it doesn't like and is deactivating the system. My suggestion would be to either remove the solenoids and ohm them out. A good solenoid is about 13-16 ohms. Also apply power and ground to them. There should be an audible click when energized, and it should be pretty loud/distinct. If they fail to do that this is possibly the problem.

[SpitShine_PL]

I got my hands on the full air suspension diagnostic procedure from Ford's MY'00-04 electronic FSM (it's a print to PDF from the relevant section, and boy, it's extensive). I read the whole section and there are several takeaways to consider:
1. SuperStar 2 is required for function tests, which gauge how the air suspension module responds to the required inputs for the air suspension to work, trim the rear height and drive the system components (the air spring solenoids, the vent solenoids, and the air compressor). A lot of those tests can be replicated by forcing input to the controller or the system components, as appropriate; what you cannot replicate without SS2 is the tests by which the controller waits for specific inputs and returns the DTCs on the SS2 display. You need to grab the circuit diagrams and follow the diagnostic procedure with a test light and a digital multimeter to test for power / continuity on each circuit relevant to the system.
2. The system-wide continuous loop must be closed or the Check Air Suspension light comes on; the controller expects outputs from the ride height sensor, the EVO module, and the door courtesy light circuit (the last one drives the check and adjustment of height caused by a change in weight, i.e. the occupants / cargo on and off the car).
3. I know for certain that both air bag solenoids are OK, they're new and respond to the driving voltage on the inputs. Hence, it's either the replacement ride height sensor, which I will test today with a regulated voltage source, or some wire is open or short to ground - any of the inputs / outputs which drive the components, like a bad connection between the controller and the door courtesy light output the controller needs.
4. I already tested for a bad compressor relay; the Check Air Suspension light came on nevertheless, I opened and closed all the doors in succession. The expected response is the compressor to pressurize (evident by the BRRRT) or vent (evident by the compressor vent soleonoid clicking [[and a hissing sound of released air--in my case no hiss would be heard, since the car still sits on the coil springs]]).
5. It's back to rudimentary diagnostics with a digital multimeter and a test light to pinpoint the fault.
6. Of note: yeah, my GrandMa has the digidash.

I'll keep you posted on how this develops.

[SpitShine_PL]

PS.
I found the air suspension test connector. It lives on the LH fender, right to the aft of the washer fluid tank. It is secured to a mock receptacle which has no wiring but a bridge / jumper wire between two pins (the bridge is factory, it still has a MADE IN MEXICO tag intact). I wonder what that bridge does.

[SpitShine_PL]

PS.
I found the air suspension test connector. It lives on the LH fender, right to the aft of the washer fluid tank. It is secured to a mock receptacle which has no wiring but a bridge / jumper wire between two pins (the bridge is factory, it still has a MADE IN MEXICO tag intact). I wonder what that bridge does.

Oh geez, correction: the test connector is where it should be, aft of the air suspension switch in the trunk, LOL. I confused it with one of the two connectors on the LH plastic wheel arch, behind the washer fluid tank (and I don't know what these two are for. Yet.).

[jaywish]

How did you do the test? With the height sensor in you hand?

Jay

[SpitShine_PL]

Jay

Whaaat?

BTW, ohmed out the replacement ride height sensor from Clay. The switchover pattern read by the change in resistance matches the pattern from Dereck's writeup:



...I'm puzzled tho; the ohmmeter read steady 20 ohms where the reading should be < 10 ohms; it also read O/L where it should read > 1 Mohms.
I don't know if 200% of the specified resistance is good for a sensor which runs on 3.3 volts or not.

Will have to run those tests per the FSM.

[jaywish]

When you tested the system was the new sensor completely installed in the vehicle?

If the sensor was installed was was the car up in the air? Exactly how was it supported?