What am I missing-ABS Deceleration Sensor??

[E30andy]

ABS is NOT WORKING.

I’m assusming the cause is the acceleration sensor, but are there any diagnostics that can be done on the ABS?

[Kershaw]

Is your ABS (ANTI-LOCK) light on? If it's not, you should pull the cluster and verify/replace the bulb. AFAIK, it needs the bulb to work to complete the electrical circuit.

I'd imagine that the acceleration sensor is also integral to the circuit and not having it is an issue. You might try connecting the two wires to each and then checking if your ABS works. Do this before pulling the cluster because its easier.

I have a sensor in my basement from an ix I parted out, $45 shipped ($10 for part, $35 for s/h, lol) or come pick it up for $10. Or you could buy one off ebay. https://www.ebay.com/itm/BMW-E30-325...dV2Y9K&vxp=mtr

[muuris]

ETM pic of the decel sensor as attachment.
-You can just jump the wires to simulate slippery surface (braking or not).
-Decel sensor disconnected from connector = braking on asphalt.

Haven't tested if disconnecting the sensor makes the light stay lit on startup.

Related to this, some might find interesting: the ABS system of the E30 isn't very smart, ie. you can pull off every ABS sensor and have the vehicle pass MOT. Light comes on at startup, goes away -- ABS doesn't work in practice because it doesn't have any speed reference and thinks the vehicle is stationary.

Btw, topic title could be edited to be more informative.

[E30andy]

Thanks Guys, very helpful!

Kershaw-yes ABS light is on. Comes on within a minute or so of start-up, and stays on.
I have a line on a sensor, harness, and mount from some guy on CL in NJ parting an ix. If it falls through I will take you up on your offer.

Muuris-just edited the thread title, good idea.

[Kershaw]

You're going to have to figure out why the light is on. Probably check your abs relay first.

[muuris]

Does the ABS light come on even if you don't drive the car but stay parked? From my experience I'd say hydraulic relay problems won't let the light go off invthe first place. The ABS box monitors these so it knows whether the coils and contacts actually work (can be seen in ETM and I found this out also in practice, previous owner had thrown away my relays).

If the light goes away and lights up when stationary, I'd suspect the under/overvoltage protection rely near the box or the box itself.

[E30andy]

You're going to have to figure out why the light is on. Probably check your abs relay first.

So the fact that the Decel Sensor is missing wouldn't trigger the ABS light?

[E30andy]

Does the ABS light come on even if you don't drive the car but stay parked? From my experience I'd say hydraulic relay problems won't let the light go off invthe first place. The ABS box monitors these so it knows whether the coils and contacts actually work (can be seen in ETM and I found this out also in practice, previous owner had thrown away my relays).

If the light goes away and lights up when stationary, I'd suspect the under/overvoltage protection rely near the box or the box itself.

I will have to check that out, not sure if the light is on when stationary

[flyboyx]

i would say that you should fix this issue and see if the abs light goes out before trouble shooting anything else. judging by the electrical diagram posted above, the switch is normally closed. i would assume that the abs controller is looking for this input and not finding it.

it seems so ridiculous to me that the p.o. would cut the wiring harness to remove this unless this car was a parts car at one time and it was used to make another ix work.

[muuris]

So the fact that the Decel Sensor is missing wouldn't trigger the ABS light?

I tested this, it doesn't trigger it in mine. Light comes on and goes out normally with sensor wire disconnected and car stationary.

it seems so ridiculous to me that the p.o. would cut the wiring harness to remove this unless this car was a parts car at one time and it was used to make another ix work.

Never underestimate what ridiculous things previous owners may have done. For example in mine the RH front sensor wires were in ABS-ECU connector pins 11 and 23, whereas it should be 11 and 21..

[E30andy]

Pretty sure my car was a parts car. The mount for the decel sensor is gone as well.

Found this thread in the old BMW 325ix registry....check out Satch Carlsons comment about the decel sensor, it in the top portion of the page. He notes the ABS light came on when he disconnected the sensor:

http://home.earthlink.net/~hainesinutah/members/newsletters/iXchange12.html

[muuris]

Pretty sure my car was a parts car. The mount for the decel sensor is gone as well.

Either that, or rust -- mine had a bad spot right under the mount.

Found this thread in the old BMW 325ix registry....check out Satch Carlsons comment about the decel sensor, it in the top portion of the page. He notes the ABS light came on when he disconnected the sensor:

I didn't wait 20 secs in my test, so there's that -- the circuit can be open for 20 secs, after that it lights the ABS bulb. Good find, good to know for possible future troubleshooting.


A bit of offtopic: I added ABS off-switch (cutting power from overvoltage relay) in mine in the troubleshooting/testing process, as driving the car with one missing sensor signal is dangerous. I was surprised that one had to drive ~90kmh or for a few km distance for ABS light to lit. Braking with missing sensor signal makes the car pull to the opposite direction of missing sensor (ABS doesn't let the faulty corner brakes do anything).

[E30andy]

Either that, or rust -- mine had a bad spot right under the mount.


I didn't wait 20 secs in my test, so there's that -- the circuit can be open for 20 secs, after that it lights the ABS bulb. Good find, good to know for possible future troubleshooting.


A bit of offtopic: I added ABS off-switch (cutting power from overvoltage relay) in mine in the troubleshooting/testing process, as driving the car with one missing sensor signal is dangerous. I was surprised that one had to drive ~90kmh or for a few km distance for ABS light to lit. Braking with missing sensor signal makes the car pull to the opposite direction of missing sensor (ABS doesn't let the faulty corner brakes do anything).

That's what Satch did too....added an ABS off switch.
Care to share how you did it?

[muuris]

That's what Satch did too....added an ABS off switch.
Care to share how you did it?

Hi, as mentioned it just cuts power from the overvoltage relay. So I cut the green wire near the relay, routed it through a single contact switch back to relay. Wires soldered and insulated with heat shrink tubing. This way one can switch ABS off and back on while driving, without need to switch off ignition. ABS being off is normally indicated by the fault bulb in the cluster.

I located the switch where the better equipped models have AC controls. If this is to be permanent, I'll probably seek an old Audi ABS off-switch.

edit: added pic

[E30andy]

Cool thanks for the info muuris!