['02 MGM LS] Air suspension diagnostics?

[SpitShine_PL]

MOAR NEWS: The plot thickens.
The fun part is that when I hook up the control module AND turn on the ignition, I get 12 V on both RAS-related fuses (CJB #5 and BJB #8)... and with one of the 2 connectors of the control module unhooked (with pins 1, 15 and 16), pin 16 reads 12 V (OK), and pins 1 and 15 read 7 V, instead 10+ V. Note that CJB fuse 5 and BJB fuse 8 should be all times hot.

[gadget73]

Sorry I'm just of no help here but I'm enjoying watching the process.

[SpitShine_PL]

Sure, grab a seat, brewskis, and popcorn!

[SpitShine_PL]

UPDATE: Okay, the day has been somewhat successful.
I dug through the wiring diagrams and found the splices and power distribution connectors between which the things going on now in the wiring should not happen. Can't stretch the day to 30 h, tho, so I'll certainly come back to it in a day or two, or the next weekend in the worst case.

By design, the RAS control module takes 12 V power for pins 1, 15, and 16 from two sources:
(1) Pins 1 and 15 are fed in this sequence: the source is the BJB (battery J-box), circuit 1053 (LB/PK). At splice S114, circuit 1053 branches out to several engine bay components (including the air compressor and its vent valve) and goes to C214, a HUGE multi-pin distribution connector that lives in RH footwell, on the bottom of pillar A, right hand side. Then the single wire of circuit 1053 goes to splice S411 beneath and above the glove box, where it splits to two lines down to pin 1 and 15 at the RAS control module connector.
This means there's something funky between C214 and S411, or upstream of that, between the BJB and C214; pins 1 and 15 go live with the ignition switched on and read 7-7.5 V.

(2) Pin 16 takes power from the CJB (central J-box) in the left footwell; it's circuit 298 that goes to splice S226, follows to C212 (another multi-pin power distribution connector) and comes down directly to the RAS control module. It is switched power by design. It reads 11.5 V at the RAS control module connector, which is normal.

[SpitShine_PL]

THE SAGA CONTINUES, AND THE SITH STRIKE BACK.

Meaning - we're not there yet.
Still have so little time to do this, but I keep at it.
Here's what I've done so far:
1. Decided to unhook all related connectors - from the RAS control module, the solenoid valves, the height sensor, the RAS power switch in the trunk. The height sensor and solenoid valve connectors had some grease-like gunk on the pins, so I sprayed the life outta those suckers with contact cleaner, and reconnected everything. I also contact-cleaned the steering wheel sensor pins, for the hell of it.
2. Hooked up the new air compressor, the new solenoid valves for the air springs, a known (working) height sensor.
3. Decided to repeat every RAS diagnostic test in the FSM from scratch. Who knows, might have cocked up something the last time (and I actually did with one measurement, left the voltmeter in auto and misread 1 MILIVOLT for 1 VOLT. I feel so st00pid now).

Here's what I got:
1. Pins 1 and 15 which should be all times hot are 7 V with the ignition off... and 9 V with the ignition on. FSM says 10+ V all times hot. Something's still off.
2. The steering angle sensor related pin 6 of the RAS control module is OK, the ohms check out fine.
3. Pretty much other pins and wires I've tested so far check out fine (the 11 V I found on the test connector in the trunk were... 11 mVolts. I set the voltmeter wrong. LMAO!!!).
4. NOW THE BIG THING: Shoulda started from it --
The 12 V input of the air suspension power switch in the trunk has no voltage. It should get all-times-hot voltage from output pin 2 of the RAS control module (most likely from the all-times-hot input pins 1 and 15 which get volts from the BJB, processed by the module and output to pin 2, component side).
Since it's circuit 418 which goes along a single wire without any splices or connector up to the trunk switch, I ohmed it out by hooking up the meter between pin 2, harness side, and 12 V input, harness side, of the air suspension switch in the trunk. The circuit reads 0.5 ohms, which means continuity.
It might mean the following:
(1) The RAS control module is defective. Or both are, since I god a used, known to work replacement. It can't be so, because the module governs EVO (VAPS), variable steering, and variable steering works.
(2) The wiring between RAS control module output pin 2 and the 12 V side of the RAS trunk switch is short to ground measured from the switch side and the pin 2 side, for I read 0.5 ohms on both ends of that circuit. Will have to test it per the FSM tomorrow.

[SpitShine_PL]

Went further with testing, and the Wiring Botch-o-Meter is close to the red line!

I'll repeat some things to make the findings clear:

1. The RAS takes all times hot battery power for the control module, the air spring solenoids, the compressor vent solenoid and the compressor motor over a LT BLU/PINK wire, circuit 1053 via: BJB 30 A fuse and down to splice S114, where it splits into three LT BLU/PINK wires for (2) the compressor relay driver and power feeds, (2) the compressor vent solenoid, and (3) towards the RAS control module. The third wire in circuit 1053 upstream of the RAS control module branches out at splice S411 towards (1) both air spring solenoids (this splices for each of the solenoids downstream of the RAS connector behind the rear seat) and (2) two wires for the power input pins 1 and 15 (all times hot) at the RAS control module.

2. The RAS control module input pins 1 and 15 power the module and the voltage is processed and output from the module over pin 22, circuit 429, on a 12V wire (VIO/LT GRN) to splice S431 where it branches out to the RAS power switch in the trunk and the power input of the RAS height sensor. The RAS power switch (with the contacts made) passes 12 V power back to the RAS control module with a single, continuous wire (no splices or connectors along the way) to the RAS control module input pin 2.

I attached the RAS wiring diagram to make things easier:


The friendly digital multimeter shows this:
1. The 30 A fuse of circuit 1053 in the BJB reads nice 12 V all times hot and 13 V something with the engine running.
2. Pins 1 and 15 on the RAS control module harness side read only... 1.5 V (unlike 7 V the last time!) without the engine running and 8.5 V with the engine running.
3. Pin 22, RAS control module side, reads 1.5 mV only when the engine is running. I guess the volts on pin 1 and 15 are too low to drive pin 22 which is a voltage output (FSM says that 10 V or more are normal on pin 1 and 15).
4. Since the 12 V output from the module on pin 22 has almost no voltage, the RAS switch (powered from pin 22) reads 0 V and the 12 V input for the RAS height sensor downstream of splice 431 also reads 0 V. The RAS switch side wire which runs back to pin 2 (the 12 V input from the RAS switch, grounded when needed by module) also reads 0 V at the RAS switch.
5. Circuit 1053, LT BLU/PINK wire reads 0 V at the RAS harness connector behind the back seat, so the air spring solenoids get no power; there is a fault near splice S411.
6. SURPRISE MUTHAFUCKA! Pin 2 on the RAS control module harness side, which should read 0 V because its wire from the RAS switch is 0 V, reads... 8.5 V when the engine is running.
7. The power wiring in circuit 1053 downstream of splice S114 (the first one downstream of BJB fuse 30 A) has normal 12 V for the RAS relay, the compressor and its vent solenoid.

What does it all mean? Well, the RAS CM harness-side pin 2 wire goes back from the RAS switch along harness 14A005 which happens to feature circuit 1053 LT BLU/PINK 12 V power wire and splice 411. This means the pin 2 wire is short to the 12 V power LT BLU/PINK wire (circuit 1053) around splice S411, and the LT BLU/PINK wire (circuit 1053) downstream of S411 gives no all-times-hot power to the air spring solenoid valves. S411 lives within a section of harness 14A005 right at the RAS control module.

I think I'm right these two are short to each other because (lemme repeat myself) pin 2 in the RAS control module harness has the same voltage as pins 1 and 15 powered over circuit 1053 from the BJB (the too low 8.5 V).

[gadget73]

Unplug the relay that pin 2 drives and see if the voltage goes away. You may just be reading the voltage through the coil. It appears that the splice that feeds 2 and 15 also runs that coil, and the control module grounds on pin 2 to turn the relay on.

Wonder why the voltage is ~8.5 instead of battery voltage. Does it read normally at the fuse under the hood? Something must be high resistance someplace and causing that. I'd guess the splice, but thats just a guess.

[SpitShine_PL]

The RAS fuse in the BJB reads normal battery voltage, +1 V more if the motor is running and the alt is charging.

Uhhh... Pin 2 in the diagram (and the FSM wiring diagram) should receive 12 V from pin 22 of the control module, via the RAS trunk switch (it's labelled "Pressure reservoir contol switch" in this diagram, FSM labels it just as the "AIr suspension switch"), and that's it. Look closely (the light green line that goes to the switch which makes connection with the pin 22 violet line), it does not splice into the LT BLU/PNK wiring from splice S114; S114 powers the RAS relay which is grounded from relay pin 85 to the RAS control module pin 23. (Or my eyes do something funky with my brain, or the other way around!)

That's why I think there's something funky around splice S411. I forgot that upstream of splice S411 there is one large multipin connector for power distribution, C214, it lives at the bottom of the right-hand pillar A, under the kick panel below the glove box.

It's a good idea, tho - I'll try to unplug the RAS fuse in the BJB and look for voltage at pin 2, harness side of the RAS control module, and the relay too, just for the hell of it.

[gadget73]

d'oh, thats what I get for not looking closely. I saw the switch and the speed sensor drawn above it and somehow put that together as "relay" in my head.

OK, so if pin 2 comes through the switch from 22, its quite likely that inside the module it connects from 1 to 22 so that would explain why the voltage matches. If you unplug the module there should be no connection so that would prove it out.

[SpitShine_PL]

Yeah, but I tested the volts also with piercing probes. 1 and 15 have 8.5 V when the motor is running. With all connectors hooked up to the RAS control module, pin 22 has 1.5 mV most likely that anything less than 10 V on pin 1 and 15 is not processed by the module (FSM says less than 10 V on the inputs is wrong). At the same time, pin 2 reads 8.5 V, the same as pin 1 and 15 while pin 22 is 1.5 mV.
It's funny I can't remember if pin 2 has 8.5 with the RAS module connectors unhooked and the motor running; gonna repeat the measurements.

[SpitShine_PL]

UPDATE:
Not really an update. Tested all out, it's definitely bugged somewhere in the wiring section I've identified before.

Just to let you know I'm working on welding the frame (the infamous rust attack right behind the lower control arm rear mount). She'll be fine, going back to the black top with a set of Bilstein B6 and CHE Performance rear arms and Watts link. When she does so, I'll be on my last leg to sorting out what's wrong with the RAS and, hopefully, getting it to work.

Stay tuned.

[SpitShine_PL]

UPDATE (bruh, another one...?):

The RAS project is very much alive. Didn't have the time to get around it, had the control arm frame mount welded up, she's good to go. Dropping in new cats this week, for the RH pipe ones are shot to hell and the engine is getting slightly too hot at hwy speeds.

Anyway, I forgot about one thing that is partial to chafed wiring beneath the passenger side front fender liner (the same problem Dereck had): when I run through deep puddles, the power to the radio head unit dies. I believe the power for the radio runs along a wire in the same harness (I can tell that from relay #3 in the BJB).
This might be telltale of the pin 1/16 voltage which is too low at the RAS control module inputs.

Gonna sort out the cats and resurrect the RAS (finally!).

[SpitShine_PL]

UPDATE:
The RAS project is very much alive. Didn't have the time to get around it, had the control arm frame mount welded up, she's good to go. Dropping in new cats this week, for the RH pipe ones are shot to hell and the engine is getting slightly too hot at hwy speeds.

Anyway, I forgot about one thing that is partial to chafed wiring beneath the passenger side front fender liner (the same problem Dereck had): when I run through deep puddles, the power to the radio head unit dies. I believe the power for the radio runs along a wire in the same harness (I can tell that from relay #3 in the BJB).
This might be telltale of the pin 1/16 voltage which is too low at the RAS control module inputs.
So: need to test out the volts on C214. Got a gut feeling the wiring is shot at the passenger side fender liner. Gotta pull the fender liner and see what's what, with a bunch of wires and shrink tubes at hand.

Gonna sort out the cats and resurrect the RAS (finally!).

[SpitShine_PL]

OKAY! I know I took my sweet time to get here, but this is one BIG update.

Remember that the RAS module had too low volts to operate? Tested the power line, wire 1053 (LT BLU/PNK) between the battery junction box and connector C214 in the passenger footwell, next to pillar A. Obviously, 9 volts is too low. The BJB fuse read nearly 12 V, which is OK.




Jacked up the passenger side front part of the car, propped up and the lower control arm, took the wheel off.
Removed the fender cowl (the black plastic wheel arch thingie) out of the way to get to the wiring harness that goes from the battery junction box to connector C214 and further to pins 1 and 15 of the RAS control module. It's easy, there are two M8 bolts with HUGE washers spaced under the fender cowl approximately 30-40 deg. off the vertical that intesects with the wheel hub. Just yank them out and gently prise the outer fender cowl edges from the fender panel.

What did I see at the firewall grommet for wire 1053 in that harness?
This. MMMM, CRUNCHY GREEN.



Cut off the bad parts, spliced in a new wire to match the gauge, sealed it up with shrink tubes and silicone sealant, and wrapped it up neatly in zip loom and electrical tape all the way from the grommet to the OEM split loom. Not taking chances the wire might chafe again. No way, Jose!

Turned on RAS switch in the trunk, then keyed the ignition to accessory power and BINGO!



No more RAS check light, which means the RAS system reads all wiring connections OK.

Now, to make it work, because I don't think it still works:

1) The RAS module, the height sensor, the solenoid valves and the RAS air compressor are connected (obviously, for there is no RAS check light). The air springs are NOT yet in (it still has the rear springs in), but this doesn't matter now, the RAS system wiring is complete as it should be.

2) With the ignition off, I opened and closed each door and the trunk in succession. Each time I heard a loud CLICK from the RAS air compressor. And that's pretty much it, it won't react otherwise. Turned accessory power on, repeated the door and trunk open/close sequence, and heard the compressor click each time. Repeated this again, with the engine running. I also sat in the car, got out, put some load in the back, closed the door and the trunk, etc. The compressor clicked every time.

3) Now, the compressor power relay (whicg makes the compressor TRRRK and pump, is in the battery junction box, which means it's the compressor's vent relay clicking when tested as above. The relay pins volt out OK (12 V).

I verified that the compressor works by removing its relay from the BJB and shorting the power pins - the compressor ran fine. Either I'm doing something wrong, or the RAS still needs something to start the compressor.

(I got another 'refurbished' RAS height sensor, just in case + another RAS control module as a spare.)

[gadget73]

if its the vent solenoid on the compressor you're hearing when it should be inflating, that sounds like the wiring for the vent and the compressor relay have been switched. Either that or there isn't any power at the compressor relay, and its just being pulled. Might want to jump the compressor relay to verify the circuit from the fuse panel to the compressor can actually carry current.

The vent solenoid is normally closed, power is applied to dump air from the springs. The spring solenoids are opened to either fill or vent.