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Michael Miller
Michael Miller, ASE Certified Technician
Category: Audi
Satisfied Customers: 241
Experience:  ASE Master Technician. Audi certified, including R8 and TDI (clean diesel).
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2002 Audi Allroad Quattro: air-ride..suspension..The compressor..noisy

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<p>I own a 2002 Audi Allroad Quattro 2.5TDI, it has the audi air-ride suspension. The compressor was replaced by Audi 2 years ago due to very noisy compressor motor. The air suspesnion has been functioning normally ever since up till yesterday when I noticed the level was stuck on Level 1. When pressing the button to raise to a higher level I do not hear the cpmpressor kicking in - The green (suspension raising) light flashes and after about a minute times out with the orange "Suspension Locked" light coming on. Ignition off/on resets this conditon and is back to solid green light Level 1. Looking at the 4 wheels, the suspension seems ok - all four sides within 5mm of each other in terms of height which does look to be setting Level 1. I have VCDS (Vag-Com) software on my Laptop with the USB cable. The system keeps throwing up 3 faults when the orange Suuspension Locked light illuminates on the instrument cluster. And these are as follows. Wednesday,21,July,2010,19:31:33:21461 VCDS Version: Release 805.0 Data version: 20080730 ------------------------------------------------------------------------------- Address 34: Level Control Labels: 4Z7-907-553.lbl Part No: 4Z7 907 553 E Component: - 2C1A1 D040 Coding: 25500 Shop #: WSC 09999 3 Faults Found: 01772 - Signal from Level Control Pressure Sensor (G291) 27-10 - Implausible Signal - Intermittent 01400 - Suspension Level Control 11-10 - Control Limit Not Reached - Intermittent 01770 - Temperature Sensor for Level Control Pump/Compressor (G290) 27-10 - Implausible Signal - Intermittent ------------------------------------------------------------------------------- I see from the answer to an earlier question on this subject where the first two faults were showing up that the solution was to replace the G291 Senser. I am guessing with my problem I will also need to replace both G290 and G291 sensors. Is this correct? If so, how do I access the compressor unit where I believe the two parts are located. The answer to the other question was to first jack up the car in Jack mode (ie. suspension locked - which at present does function ok on my car) loosen the 6 hoses and replace the unit. But I don't know how to access the parts - looking at various diagrams it looks as if I have to remove the offside interior side panel of the luggage compartment to first access the compressor area. I am guessing the car is jacked up because the suspension will lower when the hoses are disconnected??? Hope you can help me on this one. If not, is is safe to keep driving the car in this condition - switch ignition on, start engine - no warning lights - suspension in Level1, just won't rise to other levels???</p><p>Update: when trying to source the parts, I am told by Audi that G290 is part of the Compressor and the whole compressor would have to be replaced.  Can you confirm this is true?  Thanks.</p>

Hello and welcome to JustAnswer. My name is XXXXX XXXXX I am here to help you in any way I can.


The sensors are integrated in the compressor and it definitely appears that you will have to replace the compressor to repair this problem. I do not recommend driving the vehicle with the compressor not cycling as it should, because the vehicle height will eventually drop to unsafe levels. It also puts extra stress on your airbags.


I hope this helps.

Customer: replied 7 years ago.
Ok so I need to replace the compressor. How do I access this please?
I'll need a vehicle identification number to access vehicle specific repair information. In general, the compressor is located under the car, directly in front of the spare tire well. Lift the car, find your spare tire well, then look for a black shield covering the compressor on the driver side of the car (between the well and rear suspension/subframe.)
Customer: replied 7 years ago.

Hi and thanks again. Here is my VIN:

Chassis Type: 4B - Audi A6 C5
VIN: WAUZZZ4B02N145734

Any detail on repair information would be much approciated.

Thanks for the information. The compressor is located where I described it above. The sensors are integrated into the compressor unit. However, I took a closer look at your initial problem description and have a few insights to offer.


One, you mention loosening 6 hoses. Those 6 hoses come out of the valve block. The valve block distributes the air produced by the compressor to the 4 air struts and the accumulator in the left rear part of your trunk. This block is separate from the compressor and should not be causing your problem. The compressor is located right next to the valve block. The compressor only has one hose and an electrical connector that needs to be disconnected.


Second, this is my take on the fault codes.

The 01400 is stored because your air suspension is not setting the vehicle to its proper ride height. This is more or less a generic code for a malfunction used to set the yellow warning light in your instrument cluster. This is not your root cause.

The 01772 is set for control pressure implausible signal. Basically, the air pressure in the system is not as specified. This is either a bad signal (due to a bad sensor) or the air pressure truly is incorrect due to a leak. Hold that thought.

The 01770 is stored for temperature. This can be a bad temperature sensor, as you have already found out from other sources. However, the sensor checks the compressor temperature, not air temperature or anything else. The sensor is designed to shut off the compressor if it gets too hot. A compressor overheats when it has to run more than it needs to, i.e. longer than what is normally needed to adjust ride height. This points to a leak in the air system, which is supported by the 01772 fault.


The botXXXXX XXXXXne is this: your compressor probably needs to be replaced, but after you do that, the air suspension needs to be checked for leaks. The concern is why did the compressor burn up after two years. If you have not replaced air bags on your car in quite some time, suspect a leaking airbag (especially the fronts.) They may only leak at a certain ride height, so do a complete check. Also, check the hoses and the valve block. The system can leak internally, but that is rare.


Finally, if the compressor did burn up, check the relay contacts. The extra current being drawn by the compressor can burn the relay contacts. The relay is installed in the relay panel behind the driver lower dash panel.


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