Subject: Here's a tidbit for ya. Author: Gcracker : member since May, 2004 : 263 posts Posted on: 2005-11-21 21:26:47

I work at a Saab-specific repair shop in Portland, Me. The most common ELECTRICAL faults are as follows:
1. Bad sensors (Inconsistant resistance)
2. Open loop sensors (No continuity)
3. Bad system/pump relays
4. Bad ground
5. Bad ECU

That's the list in order of frequency. The thing that happens most is that you test all four wheels and get the same result at a speed of one revolution per second. About 100mVac. BUT, when you test for resistance, you either get a solid value way out of spec, or a steadily increasing value (capacitance).

For example, a '94 9000 will light the ABS light. I remove the ecu and test for the sensors at the harness connector with the car in the air. When spinning all the wheels, I get Vac, but the expected resistance is 1025 Ohm, and instead it will be 22.4kOhm, steadily increasing in resistance, just like a battery charging. I'm not sure why iot happens, but when impulse-type sensors go bad, sometimes they act like a battery and actually store charge.

So don't assume the sensor is good just because it sends an AC waveform.

BTW, my '86 528 did the same thiing and it was a missing tooth on the rear impulse-rings. I ended up replacing both hubs and fixed that problem. ('course I wound up with some new ones, but that's a different story)

'88 M5 193k (Engine out)
'87 528e 211k "is" package (falling apart)

• Any way to test the ABS pulse generators? - cfisher 2005-11-17 11:09:21 (606 views)
  • Yes: Any way to test the ABS pulse generators? - jack8272 2006-01-10 15:07:36 (508 views)
    • I'd like to see that. Can you post it here or email it to me? (nt) - DavidC 2006-01-10 16:08:07 (495 views)
      • Re: I'd like to see that. Can you post it here or email it to me? - jack8272 2006-01-10 22:39:01 (533 views)
  • Here's a tidbit for ya. - Gcracker 2005-11-21 21:26:47 (582 views)
    • Thanks. I will start with the sensors first, because the teeth - cfisher 2005-11-23 11:09:52 (520 views)
      • Update. - cfisher 2006-01-03 18:34:23 (455 views)
        • Is this the ABS pulse generator you're talking about? (pic) - DavidC 2006-01-04 18:28:41 (1050 views)
          • that's the one. (nt) - cfisher 2006-01-05 12:32:10 (436 views)
            • BTW, what's a good price for the ABS pulse generator? (nt) - DavidC 2006-01-06 19:28:27 (495 views)
              • I paid $110 for one from the dealer with the BMWCCA discount. - cfisher 2006-01-09 12:06:18 (412 views)
        • Since you may need to remove the sensor at the - kff 2006-01-04 09:46:28 (461 views)
          • I'll stick with the heat shrink or tape. - cfisher 2006-01-04 13:55:39 (426 views)
    • Did you replace the rear hubs yourself? - DavidC 2005-11-22 00:45:22 (495 views)
  • I think you can check them for continuity, but to check - kff 2005-11-17 14:36:14 (525 views)
    • I guess I've narrowed it down... maybe? - cfisher 2005-11-18 11:06:24 (516 views)
      • I have the same problem with ABS - DavidC 2005-11-18 14:16:54 (536 views)
        • My wheel hubs look good, and are not rusty at all. - cfisher 2005-11-18 14:50:26 (509 views)