ABS Failure Resolved! <long> - Saab 9-5 Bulletin Board - Saabnet.com
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ABS Failure Resolved! <long>
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Posted by bobc [Email] (#473) [Profile/Gallery] (more from bobc) on Sun, 24 Mar 2019 21:35:26 Share Post by Email
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Victory:



I've learned a lot and frankly enjoyed solving this very tricky issue.

Short story:
- Confirmed diagnosis: High resistance in the wiring between the junction to the right wheel sensor.
- Remedy: replaced the wire and connector from the right rear sensor to the junction.

Long story:

At the time of my last posting http://www.saabnet.com/tsn/bb/9-5/index.html?bID=278015 I knew that the signal from the right rear wheel speed sensor was not arriving at the junction (j108-111 under the left rear seat). This weekend I set about the task of finding the fault in the 5 ft between the junction and the sensor.

- I found no other junction
- I found no intermediate connector.
- I found that the wires at the connector at the sensor were cracked, I spliced in a new connector

- when I cut the connector out I noticed that the wires were oxidized. I cut further and further up and found that even 1ft away the wires were not bright and shiny. I spliced in the connector anyway.
- With a new connector at the sensor I found that the positive wire had good continuity to the junction but the ground wire read very high resistance.
- At that point I decided to run a new wire from the sensor to the junction, which resolved the issue (I left the old wire in place. It was surprisingly difficult to remove, but labeled it as "abandoned")


Post mortem:
1 - When I first got the "ABS Christmas tree" of lights
I immediately *assumed* that the ABS module needed a rebuild.

what I learned:
- Don't assume! https://www.youtube.com/watch?v=svkgOsr7pUc[
- I mistakenly understood that the "christmas tree" is illuminated when the module is bad but in fact it is illuminated for *any* ABS failure.

2 - The tech2 showed right rear sensor fault only. even after disconnecting the left rear connector. This led me to suspect that the ABS controller rebuild was bad in some way.

what I learned:
- the tech2 "stops" when it encounters its first ABS fault. If there is a fault for rear right AND rear left, the tech2 will not detect the rear left *until* the rear right fault is resolved. (thanks ice age dave!)


Diagnostic tips:
- get a pigtail to test abs sensors. cut one out of a junk yard car or buy a new one, they are pretty standard and inexpensive https://www.amazon.com/gp/product/B07CXZQ16W/ref=as_li_tf_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=B07CXZQ16W&linkCode=as2&tag=thesaabnetwork
- The tech2 does a static test of all sensors. The car does not need to move. The static test is to check that the resistance of each sensor is within range. I dont know the range precisely but my good sensors read 1040 ohms and I'd guess a reasonable range is 1000-1500 ohms. I am sure that it does additional test as the car is moving as well.
- The tech2 sees only one abs fault at a time. Resolve it, and if there are more they will appear.
- Once resolved, the code will remain until manually cleared. I don't know if it tracks that the resolved issue is an old code, and I dont know if it is removed after a time. But it was disorienting to see a code that I knew for a fact was resolved.

If you are using a tech2 to diagnose ABS issues, be aware of the (what I'd consider) odd behavior. As an example here is a sequence of codes that you could see:

1 - disconnect the right rear sensor
2 - read codes: "right rear no signal"
3 - connect sensor, read codes: "right rear no signal" (even though you have "resolved" the issue)
4 - clear the codes, read the codes: "no codes"
5 - disconnect right rear, read codes "right rear no signal" (expected)
6 - disconnect left rear, read codes: "right rear no signal" (It does not see the left failure)
7 - connect right rear, read codes: "right rear no signal & left rear no signal" (!) (Both codes are shown even though you have resolved the issue on the right. However resolving the right side allowed it to "see" the left fault. )
8 - clear codes, read codes: "left rear no signal" (expected)
9 - connect left rear, read codes: "left rear no signal"
10- clear codes, read codes: "no codes"

I guess I'd say that the Tech2 is ... quirky! Actually I dont know if it's the tech2 itself, or the way the ABS controller discovers, reports and stores codes. So maybe it's the car that's quirky afterall, but we know this :-)

My inexperience made diagnosis a little difficult. I saw the weird (quirky) data (illustrated above) and I started to doubt the tool and the controller. These results drew my attention away from the actual problem, leaving me to wonder "does my counterfeit Tech2 have a bug?" or "Is my ABS controller faulty and therefore reporting bad results?".

Once I understood the results that I was getting the diagnosis became much easier and I was able to move forward.


->Posting last edited on Thu, 9 Jul 2020 08:31:45.

_______________________________________ '08 9⁵ 2.3T SportCombi, Polar White '01 9⁵ Aero Midnight Blue (benched) '00 9⁵ Aero Midnight Blue (rescued) '99 9⁵ Base model, Cosmic blue '00 9⁵ Aero Silver (RIP - transmission )


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