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Old 11-12-2010, 12:04 PM
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bluebee bluebee is offline
Seek to understand,^Value
Location: San Jose, California
 
Join Date: Mar 2008
Posts: 22,005
Mein Auto: 02 BMW 525i M54 auto 130K
You didn't mention if you had all three yellow lights, ABS/BRAKE/DSC, so, maybe your problem is different, but, by replacing the wheel speed sensor without (presumably) first testing it, you're just throwing money at the problem.

Here is my standard cut-and-paste response for the ABS/BRAKE/DSC yellow trifecta ...

(All this information is from teaming up with Bill (540iman) and gathering additional details from BlackBMWs, BMW_n00b13, TheStig, Edgy36-39, Max_VQ, PharoE39, freewilly, BAMF, and others).

Three solid yellow ABS/Brake/DSC lights almost always indicates a classic BMW problem:
1. Go to the first thread in the E39 forums (the VERY best of E39 Links)
2. Search for ABS (you'll find this post)
3. Click on this canonical summary in that post (in addition, see Bill's 'logic' of testing ABS sensors).
Note: The lights may come on all at once, or one at a time, and they may be intermittent, and in the beginning they may go out when you restart the car but come back; eventually they become lit solid all the time. It's all the same problem when you have the ABS Brake DSC trifecta!

Luckily, almost always, resolution is quick, simple, and reasonably inexpensive:
- Quick: In a half hour with a DMM, you'll know exactly what components failed;
- Simple: Removal of speed sensors (<$100 each) and/or the ABS control module (<$500 new) is a ten-minute job each;
- Cheap: My ABS control module rebuild cost me $150 USD, in toto, including tax & shipping (most people report successful rebuilds under $300).

In summary, the flow-chart procedure to follow (summarized from this thread) is:
a. Open the hood, disconnect the ABS control module harness & check the four wheel speed sensors with a DMM;
b. If any wheel speed sensor tests bad, doublecheck at the appropriate wheel; replace the bad one with an OE sensor (<$100, rarely more than one!);
c. If all four speed sensors are good, simply send your ABS control module to BBA/MM/ATE (recommended in that order) for a rebuild ($300-$150 in toto);
d. If the rebuilder can't repair your module (takes about 5 days overall), buy a new module ($480 from Jared at EACTuning) & have the VIN recoded at the stealer (about $120).

In almost all (if not all) ABS, Brake, & DSC light trifecta situations, it's that simple!

BTW, while your ABS control module is out of the car (about 5 days), the following anomalies may occur:
- Brake/DSC/ABS trifecta solid yellow lights (on the instrument cluster)
- Service Engine Soon (SES) solid yellow light lit (on the instrument cluster)
- No ABS (upon hard braking under low-traction conditions)
- No traction control (DSC or ASC on lateral action)
- No speedometer (use a portable GPS navigation unit if you're worried about that)
- No odometer (again, use a portable GPS unit if this bothers you)
- No tripmeter (use a portable GPS unit if it's a worry to you)
- No cruise control
- OBDII diagnostic trouble code DTC P0500, i.e., bad speed sensor (clear by driving or with an OBDII scanner)
- No possibility of passing (California at least) smog inspections (until you replace the ABS control module & clear the DTC)
- No speed-sensitive automatic door locks (if enabled at the stealer)
- No GPS (if you have navigation)
- No mileage calculations on the instrument cluster
- No fuel consumption calculations on the instrument cluster
- No range indications on the instrument cluster
- No speed-sensitive radio (if equipped)
- No speed-sensitive wipers (if equipped)
- Erratic fuel gauge (especially when near empty, so keep the tank at greater than 3/4 at all times)
- Erratic transmission shifting (if automatic; if it bothers you, switch to manual shifting)

SUMMARY:
The problem is usually a single wheel sensor goes bad (wires or the <$100 sensor), or the ABS control module goes bad (a steel resistance-welded wire lifts off its bond pad, Bill kindly ran a full autopsy here). Debugging is best done with a DMM; an OBDII scanner can ONLY find "communication errors", i.e., it cannot tell a bad speed or pressure sensor from a bad ABS control module and will often report the wrong problem because it isn't inserted BETWEEN the ABS control module and the various sensors (see extensive reports by 540iman on this). The ABS control module costs ~$150 to $300 to rebuild, ~$500 to replace; if you put anything back on other than your original ABS control module, the VIN will need to be recoded (15 minutes with a GT-1 or Autologic or similar; impossible otherwise). You'll need to clear your OBDII DTC codes after you fix everything if you plan on passing smog tests that week (ask me how I know). If you need to replace a speed sensor, don't go aftermarket; get as close to OE as possible.

Before you send your ABS control module out for rebuilding, please consider opening it up first, post pictures to Bill's ABS autopsy thread (the rebuilders say they work on previously opened ABS control modules all the time). If you fix the broken wire, post that to the thread as a success story!
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