ABS fault - Rear Left Wheel Speed Sensor

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Thread: ABS fault - Rear Left Wheel Speed Sensor

  1. #1

    ABS fault - Rear Left Wheel Speed Sensor

    Unfortunately no-one had written a how-to guide or tips on how to diagnose and fix it. So I thought it would be helpful for those experiencing a similar issue and want to do it themselves, or if a garage has misdiagnosed the fault and replaced the expensive wheel hub+abs sensor combined unit and still has the fault. This is my first how-to guide I've written, so any feedback on it is most apriciated!

    My ABS+traction+stability control packed up last week and flagged up a error code. The ABS error code can't be pulled with a standard OBD scanner, you need either an offical GM Tech2 or alternatively an op-com.

    So I plugged in my op-com into the car and came back with "Rear Left Wheel Speed Sensor open-circuit or low-voltage". Doing a quick search of this forum I've found that others have had to replace whole hubs to fix the problem. However I came upon this post:
    https://www.saabscene.com/forum/index.php?s...&p=31738450
    With the choice of an expensive wheel hub or an expensive garage diagnostic session, I thought I would give it a go at finding the problem.

    The First Stage to verify that the loom is damaged, rather than the wheel speed sensor itself.

    The wire loom for the wheel speed sensor has two main sections. The first goes from the engine bay to a small connector box on the right hand side (from the back of the car) near the fuel tank. The second half goes from this box, splits about 30-40cm into two seperate looms, one for each wheel.

    Step 1: Disconnect the connector from the wheel speed sensor. You will need to pull the blue tab out to be able to push down the button. Unfortantly the blue-tab broke on mine, so I had to use a small flat headed screw driver to shift the blue plastic under the connector to unlock it. Remember to tug on the connector, rather than the wire loom itself. Mine needed a bit of a wiggle before it would remove. The connector itself reminds me of the new style Injector 3 connector on the 1.9TID diesel lumps.

    Step 2: Open up the little box near the fuel tank/right suspension arms and disconnect the loom connector.


    You will need to pull the red connector out to be able to remove the two halfs.



    Step 3: Now use a multimeter to measure the resistance from each connector for each wire. You can use a small screw driver to open up the shield on the wheel speed sensor to see the wire colours. This brings the number of combination of wires to test down! A good wire should read less than 1 Ohm, and should only be readable on one connector. If you get a reading on two wires, make sure your not connecting two pins together, and if you still are then you've got a short in the loom. If so your error code, at a guess, will probably be reading something like "Rear Left Wheel Speed Sensor short-circuit or high-voltage". Either way, this isn't good.

    My loom gave 0.2-0.4 Ohms between the good wires on both the left and right hand side, however one wire (the brown wire for the left wheel) gave a reading of 6 MOhm (Mega Ohm). Most multimeters will probably read a broken wire as O.L. (Over Limit), in other words, disconnected!

    One other slight problem could be if its intermentatly connecting. My ABS originally failed as I was driving and cleared itself after a restart. About a week later, it came on permently. So you may see that all of the wires read low resitances. If thats the case, then it could either be the wheel speed sensor, or an intermittent fault. Its still worth reading through and checking the failure point in my loom (which looking at how it was mounted, is probably going to be a common problem area).

    Step 4: If you now have determined that one of the wires is broken, its time to find where it is. This part becomes bit of a pig of a job as access around the suspension arms is limited. I'm fortunant enough to have access to an inspection pit at my girlfriends parents place, but it should still be acheivable under axle stands.

    You have two options at this point, replace or repair. I originally intended to repair, but after looking at how hidden the wireloom lives, I chose to replace the broken section.

    Step 5: There are a number of points that the wire loom is affixed to. I'm focusing on the left hand side as this is the side that was broken on mine, and also happens to be the longest and hardest section for access. The first location that it was affixed was a zip-tie type mounting point in the Red ring. I chose to cut the zip-tie off and I replaced it later. The zip-tie mounting-point looks like one of those types that once fitted, can't be removed unless you break it.



    Step 6: Now remove the loom from the clamps (like the one in the green ring in the picture above) that hold it onto the rear-subframe. I found the best way of removing these, is to remove the clamp from the sub-frame first and then remove the loom from the clamp. To remove it from the subframe, slightly pull apart the clamp till you can move it, then pull it off gently.

    I disconnected about 3 of these until I came to more zip-tie type fixings as in Step 5. At this point I relised it was going to be a pain to remove the complete loom, so I decided to first check the part of the loom I had access to. It so happened that the damage was on this first section (more on which, later).



    You can see the section that I removed here:


    Step 7: If you haven't already done so, use a small flat-headed screwdriver (watch-maker style) to prise apart the dirt cover on the wheel-speed sensor connector end. See image from step below for how the connector comes apart.

    Step 8: Seperate the wire from the tube. The tube already has a split in it to allow the wire to be removed.



    Step 9: Inspect the wire in the loom for damage. I came across the following:



    You may have to look more closely for damage. The cable can be damaged inside the protective insulation and not rubbed all the way through. One tail-tail sign would be a crushed section in the wire.

    Mine had become damaged at the zip-tie connector bend in Step 5, so I would recommened checking this join first.

    Two tips to find the damaged section:
    1. Bend the wire gently as you go along. A damaged section should kink with little resistance.
    2. Failing that, as a last step, you can gently cut a part of the insulation and measure the resistance (using a multimeter) from the connector to the cut part of the insulation. If it reads as low resistance (less than 1 Ohm) then you know that section is good to that point. Seal the good sections up with electrical insulation tape.
    3. Failing that, I'm afraid your likely to have to replace the whole length of wire!

    Step 10: Fixing the damage. Several ways of doing this. Firstly you can solder the two halfs together or alternatively crimp them. I chose to crimp them as solder joints can break down over time with vibration. Also my soldering iron was at home, 30 miles away!

    I used some nifty heat-shrinkable butt-crimp connectors (I used 5A versions, which was a perfect fit for the wire) from halfords. At £2.79 for two, not cheap, but have the advantage that you can heatshrink it together to help keep moisture and dirt out. Below is the fix completed. I finished the fix by wrapping electrical insulating tape around the crimp and then the ajoining wire together.



    Step 11: As my loom was particularly dirty, I used electrical contact cleaner along the length of the cable and connector to thoroughly blast and clean the dirt off. I also sprayed contact cleaner into the ABS wheel speed connector in the hub itself for good luck.

    Step 12: Being a perfectionist, I then wrapped the two wires in insulating tape to help stop moisture and dirt getting in. Then put the wire back into the tube (surprisingly fiddly job, a small screw driver can help keep the two halfs of the pipe apart). I then wrapped the tube in insulating tape again to help stop any other dirt and moisture getting in (!).

    Step 13: Fix the loom back into clamps on the rear-subframe.

    Step 14: Use a zip-tie to reaffix the loom to the zip-tie mount nearest the wheel-speed sensor (from step 5). I had to bend the cable so it didnt rest (and hence rub) against the wishbones themself. It took a bit of jiggling of firstly pluging in the wheel speed sensor and bending.

    Step 15: Reattach the wheel speed sensor connector into the hub (if not already done so). Push the blue tab back in to lock the connector - or if you broke it like I did, use a small screwdriver to push the blue mechanism across.

    Step 16: Connect the connector back together near the fuel tank/right wishbone. You will need to push the two halves together while pushing the red part back in. In pushing the red part, the two halves will be drawn together. Close the lid of the box.

    Step 17: Make sure that you've plugged in the other wheel sensor connector back in. I, for good luck, disconnected it and gave it and the connector in the hub, a good spray of electrical contact cleaner.

    Step 18: Turn on the car ignition and hopefully the error will have disappeared! As a final step you may need to clear the ABS fault code from the ABS module using op-com/tech 2. However this isn't compulsory as the system will operate fine.

    I hope this helps anyone who comes across this problem in their Saab.

    Total repair cost: £2.79.
    Time: about 1-2 hours (I'm a perfectionist, so probably take most people an hour at most).
    Difficulity: Simple, but can be fiddly around the loom clamp mounting points.

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  3. #2
    Mega Motor Mouth saabman's Avatar
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    Nice one, and good write up!


  4. #3
    Saab Nut ambisaab's Avatar
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    Excellent write up and quality pics. 'How to's' take a lot of work and I thank you for it. If any Mods read this how about a 'How To' section at the top were we can put them all together.

  5. #4
    Thanks for the feedback.

    I think a How-To forum section (or even a sub-section if the forum software allows it) would be very useful. As these cars get older (and are now cheap second hand) I think there are going to be more and more people wanting to fix it themselves (assuming generally if someone has bought a car cheap second hand, they're less likely to want to pay out for a garage to fix it), especially as this mark 9-3 has plenty of common faults that most of them can be fixed relatively cheaply. I know if I have a problem, I'll check to see if some-one has done a How-To guide on the problem and assess if its within my abilities to fix it or take it to a garage.

    If anything, it may help the second-hand value, as people who are Googling before they buy a 9-3 can see that there are common faults, and that the majority of them aren't that hard to fix. It may even persuade some of the current 9000/old 9-3 owners to start looking at changing up to the 2003+ 9-3 (!), after all they both have their share of common faults.

  6. #5
    Saabisti CombatCrew's Avatar
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    Really impressed! Excellent write up and plenty of good pictures. This actually happened to me a couple of years back during a really icy spell. Took it to the dealers due to the fault codes and they managed to find the wire and repair it for £120 Which given the weather and the fault diagnostics suited.

    Paul

  7. #6
    Very nice! I had similar problem and was so close to buy rear tire hub. Then I found this and fixed the problem. Thanks a lot!
    Btw, I think that delphi wires used in Saab ABS system are junk. So thin and poor quality.

  8. #7
    Regular Saab Guy
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    Just read your great write up. Had the exact same problem this week, started with abs malfunction then tcs turned off then brake failure contact service /?? This was 5 in the morning so called the AA great help !! would only tow me to nearest Saab garage 10 miles away, I was going to work in Essex and was already 110 miles from home and needed to get to work so after a little chat agreed car was safe to drive, possible sensor failure , he said my discs could do with changing, so when I got home on Friday local garge fitted 4 new discs and pads but could not turn off the EML bookeed into saab garage where they cleared the numerous fault codes and then discovered the exact same fault as yours the dreaded wiring almost the ame place as well looks like its going to be a common fault. Any all fixed now and main dealer only charged £108 phew sorry that was long winded just trying to make the point about the [expletive deleted] wiring ////////////////

  9. #8
    Great write up. I'm having the same issues with my 2006 9-3. When you were diagnosing this, did you notice your gas mileage and your trip gauge calculating half? My mpg is down to 12, usually around 25 and my trip gauge says it was only a 4.2 mile drive home from work when it's really closer to 8.5.

    Thanks,
    Joel

  10. #9
    Saab Junior
    Join Date
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    Wigan, Lancs, UK. 93 1.8t VSA 2005
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    Just had mine repaired today and it was recording about half the miles I was driving on the milometer and half MPG. Speedo was fine.

    Follow Simon_C's instructions and all should be good.







    Info on my problem:
    https://www.saabscene.com/forum/index.php?s...=#entry31765156

  11. #10
    Glad that it helped, and hopefully save you a few bob repairing GM's rubbish attention to detail.

    I don't think there was any difference on my MPG and distant counters. My car is a diesel, so not sure if they're calculated differently. Or maybe the distance is calculated from the rear right wheel? I don't know. A bit rubbish that it does do that though, as it would be an easy/cheap/crappy way of slowing down the amount of mileage that a car accrues. Plus the system still has 3 other working sensors to accurately calculate the distance, no excuses from the Saab engineers in my opinion!

  12. #11
    Does anyone know of an auto store (like autozone, advance auto, napa etc) that will do a free tech2 diagnostic check? It seems like the engine code scanners at most of the stores that will do it for free don't work with Saabs.

    Maybe I'm going to the wrong place though, I usually only try autozone since it's closest. Most garages I call won't even hook up the tech2 scanner unless I pay for at least 1 hour diagnostic. I hate to toss $80+ for someone to just hook a small device up that is done in 10 seconds with an answer.

  13. #12
    Does anyone know of an auto store (like autozone, advance auto, napa etc) that will do a free tech2 diagnostic check? It seems like the engine code scanners at most of the stores that will do it for free don't work with Saabs.

    Maybe I'm going to the wrong place though, I usually only try autozone since it's closest. Most garages I call won't even hook up the tech2 scanner unless I pay for at least 1 hour diagnostic. I hate to toss $80+ for someone to just hook a small device up that is done in 10 seconds with an answer.[/b]
    Unfortunately thanks to GM, the Tech2 system that is kept regularly updated is an expensive system, so most garages with it need to make a return on their investment. Most general garages will be able to read standard error codes with their scanners, however most won't be able to diagnose any other system on the car without a Tech2 - such as the ABS module.

    If you want to just read the error code off such modules and not do more advance features (such as actuator tests), there are third party systems such as OP-COM that do it.

    It really irritates me that its not possible to do a full diagnosis and repair of most modern cars without having extremely overpriced proprietary diagnostic tools. My plan at some time is to reverse engineer the CAN-Buses on the car and open-source document it, to eventually produce some sort of cheap third party diagnostic tool. Apart from making it easier to repair, I reckon it could help second hand costs (like the VAG-COM) by making people less fearful of expensive, dealer-only repairs. Well that's the plan anyway. *adds it to the long list of projects*

  14. #13
    Saab Junior
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    Great write up. I'm having the same issues with my 2006 9-3. When you were diagnosing this, did you notice your gas mileage and your trip gauge calculating half? My mpg is down to 12, usually around 25 and my trip gauge says it was only a 4.2 mile drive home from work when it's really closer to 8.5.

    Thanks,
    Joel[/b]
    Your issue sounds the closest to the problem I've just had fixed (ABS, ESP, TCS errors + half mileage and half MPG being recorded). Forget the Tech2 for now and see if you can get your car raised and check the wiring from the right rear speed sensor (looking from behind your car) to the junction box near the petrol tank. A circuit line tester will show which wire is at fault, and you could see the damage to the wire once the trunking had been removed regardless.

    Forgot to mention on an earlier post that this repair has also fixed another issue with my steering lock not working. Maybe a coincidence, but it started working immediately after the ABS errors had stopped being reported on the SID.

    Good luck.

  15. #14
    Saab Junior
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    Simon_C, could you post the model number of the OP-COM that you use or recommend. I assume they ship the PC software also or does this have to purchased seperately?

  16. #15
    Hey I'm still working on this on and off. It's taken me a while to get some free time to fix this, but I've got one more question. How do you know it's wiring and not just a bad speed sensor?

    I can't find any indication it's in the wiring, but I don't really know the likelihood that a speed sensor just goes bad.


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