not your typical ABS repair option?
 

O5 A8.

I'm getting the P0501 left front speed sensor, EPS and ABS problem intermittently. P0501 - Vehicle Speed Sensor (G22), Range / Performance

This causes the EPS and ABS lights to come on. It is intermittent, ok one day and fail the next day. With the speed sensor malfunction, the ABS does not work nor does the speedometer. Variable speed power steering is also screwy. (sluggish or over sensitive, depending on speed the sensor goes out)

Additional codes read include:

Auto-leveling suspension: (Can't imagine what this has to do with ABS)
01316 - ABS Control Module

P1653 - Please check DTC Memory of ABS Control Module

Also, switching the speed sensor from left front to right front causes it to flag the right front speed sensor. With sensors swapped, I would have thought the speedometer might start working but it didn't. Swapping back to original positions and only the left front sensor shows bad.

Note, this is not a solid fail. EPS, ABS and associated power steering could be fine tomorrow and last for a few days.

I've been searching the forum (found one extensive thread where a newbie wasn't exactly wining friends / influencing people) and thought I stumbled onto a political debate). On one of the threads, there seems to be a connection between the ABS module and the elect parking brake. Mishar will recall a year or so ago helping me out with a used motor which seemed to fix the problem only to show signs the brake module might be bad. So I decided to live without it.

Recently, I experienced a situation similar to "Close encounters of the third kind". My brain said, "This means something", but I didn't try to shaped the mashed potatoes into an Audi. I was on the road and it started missing. I found a shop that replaced a coil pack for me. Shop cleared codes and voila! When I left, the parking brake warning which I've been living with for a while, stopped warning me. At this point, the EPA/ABS fault wasn't showing. I even tried applying the elect park switch and it worked, which tells me motors are working. I was in heaven thinking everything was good. However, driving for a couple hours and beeeeep, EPS/ABS and speedo not working. Within a second after EPS/ABS warning, the elect park brake warning came on with more beeps. This is where I thought, "This means something"

I have been able to verify a repeat this working/fail situation. Everything is fine first thing in the morning, then after a hour or so...beepy beep. First the EPS/ABS, then the elect park brake. I can drive it like this, being careful on ice, knowing the ABS doesn't work. I also am careful when the power steering thinks the car is going zero and gives me way too sensitive steering at 55-60MPH. Yeah I also watch for cops with no speedo.

Is it possible the ABS module is common to both the EPS and the elect brake? I'm leaning towards the ABS module and mistakenly thought I might get a rebuild like I did for previous Audis with the typical ABS/Brake fail for $99. Somehow, I don't think that's going to work.

I'm now suspecting the wiring somewhere in a harness or a ground might be the problem.

Any thoughts on where to look?

Hmmm, I'm often the one with the Dale Carnegie allusion that most seem to miss, so maybe I was in that prior thread too. :eek:

Meantime, right at the end of your explanation you got to my thought. BTW, thanks for good backgrounder. Helps assess/provide ideas/feedback better. Thus, harness around the ABS module and drivers wheel area? It has come up before. I have also suggested it in the past when folks have these multi system "possessed" sorts of issues, along with the surprisingly simple failing battery. I recall an old post where someone dissected the harness and found wire insulation literally falling off. Had pictures. Reminded me of electrics by Lucas of yore. I noticed your coil packs discussion and seemingly fleeting magic cure. Think not about the tie to the ignition system, but rather someone was physically in there on the driver's side moving things around to get to the head and plug area. The old, shake the wires and see what happens diagnostics of yore.

I have a W12 so ABS is positioned a little differently and it is more jammed there with the whole extra air box. Thus I can't visualize yours fully, and am also blurring some of my old C5 A6 4.2 experience with same general unit position and wiring (though pre-ESP). I would consider first getting a roll of old school cloth electrical tape--to make it look more "factory" post work. Audi also sells some tape that mimics factory look and it really tough; looks sort of like cloth bike handlebar tape with adhesive on steroids. I buy a pricy roll about once every 5 years. Anyway, with supplies in hand, unwind or carefully cut the tape or plastic jacket around that main harness area and get to the individual conductors underneath. Unclip connectors or hold downs temporarily as needed. If it is something like the W12, better access may really be from underneath by pulling fender liner. If all good, wrap up the patient and move on to other ideas. If things are falling apart, you have more work to do. From the old post IIRC, it was a fair number of wires, including ABS sensor ones he found has lost a lot of insulation.

The ABS, ESP and EPB (electronic parking brake) and almost all other systems in the car rely on speed signal from the ABS/ESP unit. The ABS/ESP unit takes in a speed signal from each tire, rounds them up, and displays a speed to the instrument cluster speedo. This is the most obvious thing.

BUT, the speed signal is also used in almost EVERY other control unit:
ECU(s): Engine braking, electronic thermostat control (82ºc over 180km/h)
TCU : Gear shifting and torque converter lock control
Air suspension: Dynamic mode after driving 110km/h for a while, lift-mode off after 60km/h, jacking-mode off after moving etc
Comfort control module: Disabling trunk and fuel filler opening when car is moving
MMI: Disabling certain menus (seat control) when car is moving
EPB: Disabling EPB diagnostics when car is moving to avoid accidents from triggering the EPB on a highway etc
Vertical light control: To move the driving lights less when the car speed is higher
Parking aid: Park aid off after 15km/h

And the list goes on :)

So now you understand that if you have a failing ABS sensor that gives erroneus data to the ABS/ESP control unit, it cannot for certain know what speed you are driving. This causes the EPB error and also ESP.

Have seen this on every A8 i've driven a bit more. Both mine (one error after driving with wildly spinning wheels), the second now in the winter with my 2008 W12 under full acceleration, ABS/ESP light comes on, and goes off after a while or re-start. Friends 2005 V8 TDI, there is/was a connector problem in the steering wheel position sensor in the steering column. Triggered ESP, ABS and EPB errors. Went on/off for 5-6months then disappeared. Triggered By empty battery, and no help even with NEW battery, even if we charged it full and cleared the DTC:s for several times.

Yeah pretty good faultfinding there with moving the fault to another wheel.

Like the other guys have said the car shares lots of info and something you may think not pertinent actually is .

The EPB i can totally understand because it needs to know the speed signal and work in conjunction with the ABS unit to bring the car to a stop should you pull up on the EPB switch while the car is in motion.

Pages 41 to 53 will give you some idea of the complexity interesting read too.

I would go straight at changing out the wheel speed sensor and take it from there.

As mentioned already wiring can get flaky on these so keep that in mind.

Heres the tape mentioned.



Also I would recommend that before you connect the speed sensors back in you give the contacts a good going over with either of the following links.

Amazon.com: stabilant 22



The Stabilant 22 is what Audi recommend you use but the other cheaper one will help improve the connection reliability.

Next step???
 

FYI, I am not doing the diagnostic or repair work myself. Rather calaborating with a shop that is respected locally for electronic repair. He has worked on many A4 and A6 but admits the A8 is a challenge and detailed information is scarce. As suggested by a couple of you, he (Dan) pulled the fender well cover and dissected a bundle of wires. It looked like old time handlebar tape wrapped around the bundle. It looked like factory original. Inside the bundle, he found two pairs of wires, both pairs the same color (brown and black) which went to the left front speed sensor. Both had crumbling insulation and bare spots which were touching. He replaced both sections of wires, cleared the codes and everything was fine.... for about a 20 minute drive and everything went back to original fail mode. It's possible there are other crappy wires in the bundle but it is not accessable without cutting the car apart.

The next day, he replaced the left front speed sensor. Again, fine for abou 10-15 minute drive. Of interest and consistent with my experience over the past 2 months of so, there is no rhyme or reason when it fails. It can be when driving along, coming to a stop or even stopped at a light sitting when it decides to poop out. At this point, the error would not reset. I picked up the car and he was stumped. After spending several hours each day for 4 days he is stumped. I had also asked him to change the right Xenon bulb, which he did. When I saw the invoice for only $50 buck, I couldn't believe it. In addition to his being out of pocket about $100 for the speed sensor, I figured it would have been in the $400 range for labor. I tried to give him more but he said, "he didn't feel right charging me and not fixing it". On Monday, I'm going back with a dozen donuts for him and his guys.

In regard to not being able to reset the EPS/ABS and non working speedometer, presto, all it took was a night parked in my garage. Next day everything is fine, but of course crapped out when driven for 20 minutes. Sometimes it has been ok for a couple days, other times, it boinks out in 5-10 minutes. I wonder if I slept in the garage overnight, my prostate problem would be fixed?

Any suggestions? My option is to live with it, doing without EPS/ABS and speedometer. I can live without the elect parking brake as I have for a 10 months but will yank the two 30A fuses to stop the annoying beep. However, it would be nice to find a magic bullet.

I have a friend who used to be an Audi Tech, whenever something like this comes up they just replace the wire loom in whichever area they think the problem is. You might call around to a junk yard and see if you can fined a wrecked car with the same issues. Not sure how easy it will be to fish out the old one and feed through the new one. But it will save you from having to find every wire with bad insulation.

I would still focus on harness, more so since you found bad wires and insulation. Confirms my suspicions and prior posts I've seen back some years now. Huge clue w/ the bad wires. If you found some, expect more, including along same conductors beyond where you dissected it so far. As other responder already suggested, maybe try to get this section of harness from junk yard, starting from the ABS unit connector for (at least) several feet and then splice in to what you have. Preferably a newer one or a CA/FL/Southwest type car.

By the way, I suggest using connectors like these for splicing if you don't already know of them. Certainly no tape type stuff or crimp connectors. These are very trick. Self soldering w/ a heat gun and shrink tubing/insulation all at same time. I used them on W12 O2 sensors that have a TSB for bad end connectors. Those are super sensitive to any wiring issues (maybe like the ABS situation...), and it 100% nailed it for me. Available for different size conductors too once you know the general product.

Also, given you found bad wires, you can/should also test out at the pin out level. Unplug ABS unit and then test it pin by pin to other end, esp wheel sensors, but also any where else you perceive flakiness, like maybe ABS unit to ECU.

Pin outs and harness destination?
 

After reading yours and other posts. (every A8 has wire problems), I'm wondering if any junker, regardless of location of climate would be better. Perhaps testing pin outs would be best but I don't have a diagram. Can anyone help me here? Starting with the ABS connector where does this harness go? Is the driver footwell kick panel a destination or does it go to the dash?

I don't agree with you every Audi has wiring problems. Every forum though has problems...sample bias. Given location of the ABS and harness, it seems to me it is vulnerable to road spray since the fender liner and belly pan are not completely water tight, and then correlation to climate seems apparent. Throw in some disguised and resold Katrina and other specials for more unfortunate stuff.

For wiring, you need to get a shop manual. You should have one at this level of work in any case. All I can tell from casually looking at line is some of the harness indeed seems to head to dash/footwell area. Under there you have one of the principal fuse panels (on side of dash), various relays and probably a main backbone for front to back routing.

Finally, if you think you got somewhere with harness repair, run a new scan and see if it is pointing at anything specific. Post a clear that is for any pre work issues. Ideally, scan it while it is doing its flaky routine.