Service Air Suspension...Again!!! HUMTECH

[14u2nv2]

Started getting the "Service Air Suspension" message intermittently, but the air suspension still inflated and maintained ride height when the truck was running.

Sometimes (but not always), when the truck was parked overnight, the air suspension would deflate overnight, but would re-inflate as soon as the truck was started.

A few days ago, whenever I started the truck, the compressor would run for about 30 seconds and shut off and the "Service Air Suspension" message came on without raising the suspension (sitting on the bump stops). Every time I start the truck it does the same thing, and the compressor only runs for 20-30 seconds and does not raise the suspension (either side).

The compressor seems to be working OK and the air port/hose work when I switch the air compressor on with the switch in the rear of the truck.

I bought new air springs, since the truck's a 2003, and figured it's about time to replace them anyway. When I pulled the driver side air spring, I checked it for leaks and it had a very tiny leak--not enough to cause the problem, so I checked the air line while the compressor was running and no air was coming out of the line on the driver side.

So I bought a new driver side height sensor and still no luck. Nothing has changed and I still have the same problem. No air coming out of the driver side air line and the compressor shuts off after a few seconds.

My local dealer, that used be a Hummer dealer is now just a Cadillac dealer and seems to be a little clueless. The nearest hummer dealer is about 30 miles away and I don't want to drive the truck too much on the bump stops.

I know that the ride height needs to be calibrated after a sensor change, but is it possible that it would not work at all with a new sensor until calibrated?

I can get a new compressor for about $400 and am tempted to do this, but that won't solve the problem if it's a calibration issue.

Any other tricks to dianose this?

Any help is greatly appreciated,

John

[Planohummer]

1)there's a recalibration out for ECAS module-have your dealer do it. should cost less than $100

2)There's an updated design compressor available.

most common failure is exhaust solenoid or overtemp fault. You can't get parts from GM, gotta buy the whole compressor. The compressors are made by Trelleborg - UK division, they might sell you components.
http://www.trelleborg.com/en/Automotive/

[Easy Ed]

Hope it is not the air inlet filter that the services manual does not mention.

Post Link http://www.elcovaforums.com/forums/s...air+suspension

I think this may have been the problem. would have changed it if I knew it was stuck up and under the drivers rear fenderwell Restricted air flow to the compressor, caused it to heat up and shut down til the next start up and then all over again.
Attached Images

[HUMTECH]

If the compressor runs for 20-30 seconds without a height change it will set a code and disable the air ride. If your positive you have no leaks it sounds like the compressor may be too weak to inflate the springs. As easy Ed said if the inlet filter is plugged this could also be the problem, no inlet air=no output from compressor. Check the filter, if its plugged remove it and see if it works. If thats not it try to raise the rear of the body a few inches with a jack under the receiver hitch and see if the bags start to inflate, if so the compressor is jus weak. If all that fails a new compressor is likely in your future, the new compressor will need to be upfitted with new air lines as well if you still have the older single stage unit. Make sure these are ordered with the new unit.

[14u2nv2]

Thanks to everyone for your replies...

Planohummer,

That's kinda what I thought it might be--a problem with the valve block/exhaust solenoid on the compressor assembly.

How long would it take to trigger an overtemp fault? The compressor stops in 20-30 seconds on it's own, but if I turn it on with the switch in the back of the truck (onboard air/hose) it stays on as long as I like. Wouldn't the compressor overheat and trigger the overtemp fault while using the switch/hose in the back?


Easy Ed,

I read your other post where you posted that photo of the filter and that was one of the first things I checked. My truck has a ceramic style filter and it looks OK.

How long did your compressor run before it shut down? Was your onboard air hose working and did the compressor stay on while you had the switch in the back turned on?


HUMTECH,

I had the driver side air line disconected from the air spring and the truck lowered all the way(to make the sensor think it needed to be raised)and no air was coming out of the air line(to air spring) while the compressor was running.

Is it possible that the new sensor is so far out of calibration, that it thinks the truck is too high(even when lowered all the way)?

Do you know the part# for the air lines if I convert from the old model to new model compressor?

By the way...Thanks for the tip you posted about rerouting the harness to the new version sensor. You saved me $150.


Thanks again,

John

[Easy Ed]

"My truck has a ceramic style filter and it looks OK" That is a bonus.

"How long did your compressor run before it shut down" Less than a minute, I think, been a while.

"Was your onboard air hose working and did the compressor stay on while you had the switch in the back turned on?" Nope

Good luck with yours, Ed

[HUMTECH]

If the compressor is running it is trying to inflate the bags so calibration is not an issue. Is there air going to the other line? if not i would say your compressor is hooped. I dont know the part numbers but any gm dealer should be able to find them, there should be a note in there catalogue for required parts when upfitting the dual stage compressor in place of the single stage unit

[14u2nv2]

I haven't checked the other (passenger side)line, but there is some pressure in the air spring, although that side isn't raising either. The driver's side air spring was completely empty before I removed it and had no pressure. I'll check the other(passenger side) line tomorrow.

Can you tell from the photo if this is the newer two-stage compressor or the older single stage...





Thanks again,

John

[Planohummer]

that's the original single stage.
the amount of pressure for lifting the truck is a whole lot more than what's at the rear aux port. This may be why the pump runs ok when it's not lifting the truck.
You really need to check the DTCs before you spend any money-make sure it's not just a height sensor recal issue or something similar. Any GM store can ck the codes for you, when you get them post them on the forum and we'll decipher.

[jarek m]

Believe it or not I had the same thing happened today:

Symptoms
- service air suspension light
- compressor runs for 20 seconds at start up
- rear end does not come up
- passenger slightly inflated
- driver side empty
- no air coming from driver side line

Already checked
- inflation system goes to well over 100psi
- driver side air bag has no leaks
- both sensors have been recently replaced
- air compressor has been changed year ago
- disconnected the battery for a while with no effect
- raised the body and cycled the compressor without driver inflating or passenger changing air pressure


Mine happened after towing my other SUV for couple hundred miles. Also ever since two years ago I changed one of the air bags then in little while each of the sensors then the compressor I never reset the system, my dealer claims there is no such a procedure!!!(Gold Coast Hummer Dealer)

[HUMTECH]

Well the procedure is lift the rear of the truck, and install the calibration blocks between the bump stop and diff housing (every Hummer dealer should have these as an essential tool) depressurize the air suspension system. With the tech 2 go to chassis, air suspension, special functions and then trim height learn. If everthing is good trim height learned will be displayed. raise the rear off the calibration blocks and remove them. close all doors, run truck and verify system works.

[HUMTECH]

And yes Plano is correct, it should be scanned to be sure prior to forking over a pile of money on parts

[jarek m]

Ok so we just got back from our NEW dealer, the diagnoses is "lack off base line for trim control". He cleared the codes and enabled the system back up for the ride home. Wednesday we go back for System and trim reset. $110 pr hour x 2 hours (he says) still comes to $ 250 with tax, good news!!!

[jarek m]

Originally Posted by HUMTECH

And yes Plano is correct, it should be scanned to be sure prior to forking over a pile of money on parts

Thanx HUMTECH!

[14u2nv2]

That's good news Jarek.


Planohummer and Humtech,

I'm having it scanned at the Caddillaic dealer tomorrow.

Is there a list of things(codes/procedures) I should have them check while it's on the Tech 2?

Thanks again,

John

[14u2nv2]

Just got back from the dealer.

It's showing a DTC C0711 --Level Control Air Pressure Sensor Circuit code. Cleared it and got the same code again.

The tech wasn't sure what that code means, and thought it needed a ride height calibration, but they didn't have the calibration blocks. I'm no expert, but I don't think that code sounds like a ride height calibration issue.

I have to admit that I was a little bit concerned when they told me that the air spring was broken because it wasn't connected at the bottom mount when they lifted it on the lift. I had to explain that since there was no air pressure in the air spring, it's not expanded. This dealer was a Hummer dealer until about a year ago and is now Cadillac.

Is the pressure sensor on the compressor assembly, maybe in the photo I posted?

Any tips on deciphering this?


Thanks,

John

[Planohummer]

Diagnostic info below. There's a new compressor module software calibration available. your Cad dealer should be able to complete this. Tell them to punch up c0711 in their service information search window and it's the only bulletin up there. here it is:


#02-03-99-002: Service Air Suspension Message Diagnostic Trouble Code (DTC) C0711 and/or Clicking Noise From Rear of Vehicle with Ignition Off and/or Electronic Controlled Air Suspension (ECAS) Compressor Cycles Too - (Nov 26, 2002)



Models:2003 HUMMER H2

with Off Road Suspension Package (RPO ZM6)

Some customers may comment on a Service Air Suspension message and/or a clicking noise from the rear of the vehicle when the vehicle is shut off and the key is removed from the ignition and/or the ECAS compressor cycles too frequently while the vehicle is running.
Cause

ECAS control module calibration issues.
Correction

For diagnosis and repair of the ECAS, follow the service procedure below.

1. <LI type=1>For diagnosis of Service Air Suspension DTC C0711, refer to DTC C0711 (SI Document ID #857738).
   Important:
   ? Before reprogramming an Electronic Control Module (ECU), refer to Adm Msg - Important Programming/TIS Information for Technicians (Admin Number 20020120 - 9/10/02) #VSS20020120 (SI Document ID #976439).
   ? When replacing the ECAS control module, the new module MUST BE reprogrammed.
2. Reprogram the ECAS control module with Tech Line Broadcast 11.75 sent to Dealers on 11/16/02 or newer. Refer to the Service Programming System (SPS) Remote Procedure (SI Document ID #820913) or the Service Programming System (SPS) Pass-Thru Procedure (SI Document ID #820915

DTC C0711
Diagnostic Instructions



DTC C0711 00: Level Control Air Pressure Sensor Circuit


Circuit
Short to Ground
Open/High Resistance
Short to Voltage
Signal Performance
Air Suspension Pressure Sensor 5-Volt Voltage Reference
C0711 00
C0711 00
C0711 00
--
Air Suspension Pressure Sensor Signal
C0711 00
C0711 00
C0711 00
C0711 00
Air Suspension Pressure Sensor Low Reference
--
C0711 00
--
--
Circuit Description

The air suspension pressure sensor sends a voltage signal to the air suspension control module that corresponds to a pressure within the range of 30-180 psi. The air suspension control module also uses this signal to verify that the proper amount of pressure is achieved in the air dryer within 23 seconds prior to opening of the inlet valves for inflation of the air springs.
Conditions for Running the DTC

Battery voltage is between 9-16 volts.
Conditions for Setting the DTC

The air suspension module detects that the supplied 5-volt reference voltage circuit for the pressure sensor falls below 4.75 volts or exceeds 5.25 volts.
The air suspension module detects that the signal voltage circuit for the pressure sensor falls below 0.5 volt or exceeds 4.75 volts.
Action Taken When the DTC Sets

? The air suspension system will be inoperative.
? The SERVICE SUSPENSION SYSTEM message will be displayed.

Conditions for Clearing the MIL/DTC

? When the fault is no longer present, DTC C0711 will change from a current DTC to a history DTC on the next ignition cycle.
? DTC C0711 will be cleared from history after 50 ignition cycles.

Diagnostic Aids

Repair all other DTCs before C0711.
This DTC is set when:

? The pneumatic status of the air suspension system is out of limits.
? When excessive amounts of time have elapsed when inflating the air springs.
? When there is a air leak in the system.
? When vehicle speed is greater than 3 km/h (1.8 mph) and rate of height change is out of limits which may be caused by a damaged LR or RR air suspension sensor.
? When the underhood fuse block 60A compressor fuse (ECAS fuse) is open.
? When the compressor relay is defective.
? When there is an intermittent or permanent loss of continuity between the compressor and the compressor supply voltage during an upwards leveling event.

Reference Information

Schematic Reference

Suspension Controls Schematics
Description and Operation

Air Suspension Description and Operation
Electrical Information Reference

? Circuit Testing
? Connector Repairs
? Testing for Intermittent Conditions and Poor Connections
? Wiring Repairs

Scan Tool Reference

? Scan Tool Output Controls
? Scan Tool Data List
? Scan Tool Data Definitions

<A href="http://gsi.xw.gm.com/si/showDoc.do?docSyskey=857738&pubCellSyskey=73030&pu bObjSyskey=857738&from=sm&cellId=73030#ss11-857738">Circuit/System Testing

1. <LI type=1>Verify that there are no air leaks in the system.
   ⇒If a leak is found, repair or replace the leaking component as necessary.
   <LI type=1>Ignition OFF, remove the ECAS Fuses in the underhood fuse block and disconnect the harness connector at the air pressure sensor. <LI type=1>Test for less than 5.0 ohms between the low reference terminal at the harness connector and ground.
   ⇒If greater than specified, test the low reference circuit for open/high resistance. If the circuit tests normal, replace the air suspension control module. Refer to Automatic Level Control Air Compressor Replacement.
   <LI type=1>Ignition ON, verify that 4.8-5.2 volts exists between the 5-volt reference circuit terminal of the harness connector and ground.
   ⇒If less than the specified range, test the 5-volt reference circuit for open/high resistance or a short to ground. If the circuit tests normal, replace the air suspension control module. Refer to Automatic Level Control Air Compressor Replacement.
   ⇒If greater than the specified range, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the air suspension control module. Refer to Automatic Level Control Air Compressor Replacement.
   <LI type=1>Verify the scan tool Air Pressure Sensor parameter is less than 0.5 volts.
   ⇒If greater than the specified range, test the signal circuit terminal for a short to voltage. If the circuit tests normal, replace the air suspension control module. Refer to Automatic Level Control Air Compressor Replacement.
   <LI type=1>Install a 3A fused jumper wire between the signal circuit terminal and the 5-volt reference circuit terminal. Verify the scan tool Air Pressure Sensor parameter is greater than 4.8 volts.
   ⇒If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the air suspension control module. Refer to Automatic Level Control Air Compressor Replacement.
   <LI type=1>If all circuits test normal, test or replace the valve automatic level control solenoid. Refer to Automatic Level Control Air Compressor Replacement.
2. Clear the DTCs and verify the system operates normally.

? 2008 General Motors Corporation. All rights reserved.

[HUMTECH]

Just make sure you dont have the newer dual stage compressor, if you reflash the module on this system it will kill the module. Only the early single stage systems had programmable modules

[fbodyguy99@hotmail.com]

what made you think you should change driver side sensor? did you have it scanned and if so what codes came up maybe i can help