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-   -   ABS light illuminates once I start moving forward (http://www.peachparts.com/shopforum/showthread.php?t=266303)

84MB500SEL 11-30-2009 11:04 PM

I'll try to check the rear sensor when I get a chance. So are the sensors the only things that could be causing this problem? As I said, the light is off at startup, but it comes on as soon as I move forward. I've cleaned out the front ones intensely and still no difference, and the resistance in them measure fine. I just wanna make sure its a sensor problem and that I'm not barking up the wrong tree. If it is a sensor problem, I'll place my bets on the rear sensor. Is there anywhere else the rear sensor plug could be besides under the rear seat or mounted on the differential? When I get the chance, I'm gonna search for all its possible locations at once.

84MB500SEL 12-02-2009 11:01 PM

So does anybody have an idea on what else it could be besides a sensor problem?

quaid 12-03-2009 09:11 AM

I had a look on WIS and the sensor is definately on the differential, not on the rear of the transmission as I thought.

On WIS the connector shown isn't a plug and socket as you would think, its a terminal block with ring connectors.

Also, it says that you need to remove the seat bench and backrest, so if you haven't already looked behind the backrest, it could be there.

Looking in the fault table, the fault for 'ABS lamp coming on whilst driving and does not go out again' is 'Wheel speed sensor cable interrupt'

So again, you really need to check the sensors and the wiring. Sensors need to be checked with an oscilloscope for a definative answer, but as previously suggested, a multimeter set onto an AC scale may give a reading when the wheel(s) are spun.

84MB500SEL 12-03-2009 11:24 PM

Just wondering, is there a way I could test the rear sensor for a signal at the ABS unit itself, like using the multimeter on the prongs of the main plug going into the ABS unit, and avoid having to find the plug behind the seat bench? If so, does anyone know what number on the main ABS unit plug corresponds to the rear speed sensor?

quaid 12-04-2009 05:12 AM

Pins 7 and 9 on the ABS computer (not the hydraulic unit).

Oh, and like I said earlier, you really need an oscilloscope to check the actual operation of the sensor. Do you know of a friend with one at all, or even a local shop?

You could even get one on the well known auction site usually for not much more than the shipping cost.

84MB500SEL 12-06-2009 12:35 AM

Hmm I'll check those pins with the multimeter I have as soon as all the snow melts away and it warms up a bit (We were just bombarded by a completely unexpected snowstorm!). If the reading is good, then I guess I'll get me an oscilloscope as advised to retest all the sensors. I just wanted to test the sensors with what I have available to see if I could find the culprit before obtaining an oscilloscope. Ill stay updated on my findings...

Thanks for the wire numbers!

84MB500SEL 12-10-2009 11:11 PM

Quote:

Originally Posted by quaid (Post 2353506)
Pins 7 and 9 on the ABS computer (not the hydraulic unit).

Oh, and like I said earlier, you really need an oscilloscope to check the actual operation of the sensor. Do you know of a friend with one at all, or even a local shop?

You could even get one on the well known auction site usually for not much more than the shipping cost.

I finally got a chance to pull out the abs computer today, but the pins on the plug are flat and have no numbers on them. Just to clarify, did you mean pins 7 and 9 on the abs control unit along the firewall under the windshield? If so, how do I know which pins are 7 and 9 since the plug isn't numbered?


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