radjaco

Hi everyone,
I would ask for profi expertise regarding the speed sensor wiring on 1997 Audi A8, 3.7 FWD engine code AEW (European). Mechanics removed the transmission and fixed the valve body. Once they assembled the car the speedometer (only one gauge in a cluster) stopped working. I checked the Speed sensor (part # 077 905 381 С or E) and found out the was manually wired (near the firewall), so that which wire goes to where is a dilemma. I removed the sensor, fixed wiring and put it back. I connected 3 wires and the car started up. However, the speedometer hand still is intact. If the speedometer hand depends on the CPS then logically if the car starts and runs, the gauge should work. I tried to search on the net the wiring diagram to make sure that the wires are connected OK, but could not find one.
Could anyone help me to explain which wire should go where and how to check that I connected them correctly?
The second question is about the same issue if the speedometer depends on ABS function. I had a problem with the right front ABS which had a broken wire. When I used to take far right than the ABS and tracking lights used to come up. Now, after I have fixed it the ABS light does not come on, but the speedometer gauge still does not work.
So, could you, guys, help me in my problem?
Thanks

hillpc

I don't know if the 3.7 front wheel drive system is any different than the code ABZ all wheel drive system I have. Don't have the Bentley manual here with me right now.

The G28 crankshaft position and speed sensor (3 wires), installed facing the engine flexplate teeth at the driver's side of the very front of the trans, is required to run the engine. It has nothing to do with the speedometer.

The G22 sensor (2 actual wires inside a 3-prong terminal), installed on the left front output shaft area of the trans, generates the speedo signal.

radjaco

Thanks a lot Hillpc for your explanation. Yes, the system on both ABZ and AEW is the same and the sensor for both is the same. Today I checked and it cranks up and drives fine, but speedometer hand does not move. Logically, if everything is fine then it means that it is an electrical problem but I do not know where to look for it. To put it in nutshell everything works except the speedo hand. I do not have the manual too. Tomorrow I am going to take it to diagnostics and erase all errors. It will also show me if there is something missing. I will post the results. I doubt, though that cleaning the memory will make the speedo hand work but will give it a shot. I just want to know what made the speedo hand stop working and where to start tracking the problem.
Thanks a lot.

jfrahm

I would imagine they goofed up the wiring to the sensor on the LH axle shaft or possibly, if they replaced that axle seal, left out the (magnetic, I suppose) ring on the axle that drives the sensor.

radjaco

You are quite right. One of mechanics told me that it should be on the driver's side caliper with an ABS sensor. I will check it tomorrow. Thanks again. I will post the results if found tomorrow.

radjaco

Another issue I have to solve is the huge red exclamation light.
1. Pads are new (practically zero front and rear)
2. Fluid is full (no leaks or loss)
3. No air in the brakes system and it functions as it should.
3. No pad sensors anymore as I have removed the sensor connectors from pads and shorted the wires in the cluster months ago.
Only thing I have not checked yet is the sensor on the bottom of the brake fluid tank. Although I have ordered the new one on ebay but have not received it yet.

Please mind that I am not an electrician and have a basic knowledge of the subject. However, I am excessively enthusiastic.
Your expertise will be highly appreciated.
Please do not advise to see the dealer or an electrician here; THERE ARE NONE qualified in Audi in this country.

hillpc

The G22 Vehicle Speed Sensor near where the left hand axle shaft comes out of the trans drives the speedometer and the odometer. Does the odometer work?

If the sensor is bad or not hooked up, neither would work.

jfrahm

Yes and if the axle flange and shaft was removed, perhaps to change the seal, the ring that drives the sensor might get left out.

radjaco

Thanks for explaining so clearly. However, it is interesting, today mechanic removed the speed sensor and replaced it with another one. However, the speedometer gauge still remains intact although the other gauges work fine. The counter and the speedometer do not move. So neither speedometer works not the odometer counts. Tomorrow will check again the speedometer in the place you specified. Can it be electrical problem> Yes, they removed the transmission completely, rebuilt it and installed it back. After this procedure the speedo and odometer stopped working. So, as I have understood I have to remove the speedometer sensor to check if the rubber ring (is it a seal?) is in its place. If it is not there, it means that seedometer and odometer would not work. Am I correct?.

Thanks again

jfrahm

No there is a ring around the shaft inside the transmission that probably has some magnets in it, and these trigger the sensor like a bicycle speedometer. To get to it you have to pull the axle, then pull the flange that this sensor snaps into.

Here is a vid showing the ring being refitted at 4:20 in:

If this ring is left off the sensor does not work.