ABS Problems

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Contents

Introduction.

It is important whilst working on the ABS system (and any car electrical system in fact) to disconnect the battery before you touch or make any changes to the system to protect from electrocution. But don't forget to reconnect it when you want to test the changes!


The E30 ABS system is adequate for stopping the average driver in the event of an emergency and is rightly so a useful safety system, if it is fitted and not working then the car is also deemed an MOT failure it is important that if it is fitted it works.

Diagnosing The Type Of Problem

If you suspect an ABS fault yet the ABS light is inoperable please skip to the next section briefly to test and repair the dash light warning system.


If the warning light is operating correctly you may use it to diagnose where in the system the fault is, put the key into the ignition and turn the key to position 1 (ATT position). The dash lights will illuminate, including the ABS light, if it doesn't its not working! Go to ABS Light Inoperable.

Keeping your eyes on the ABS light now turn the key to final position and start the vehicle normally.

If the light remains on and does not go out then the fault lies with the ABS system and is a ABS System Fault.

If the light initially goes out but returns once the vehicle moves off (or even whilst the vehicle is stationary in rare cases) but after the light has briefly switched itself off! Then it is a sensor fault (or related wiring from the sensors upto the ABS ECU). Procede to ABS Sensor Fault.


ABS Light Inoperable

If you suspect an ABS fault yet the ABS light is inoperable you may test it by removing one of the relays, on early E30s the relay is silver and can be found in the glovebox housing next to the ABS ECU, on later cars the relays (as there are two) are mounted on top of the ABS pump in the engine bay (fig 1.1) choose either or both to remove it does not matter.

If either of the fuses are missing then theres your problem. Another common bodge by bodgers to pass MOT by one of the less observant testers.

Once you have removed the relay start your vehicle, the ABS light on the dash (fig 1.2) should now be illuminated. This is because withought the relays the ABS system should not operate, you have introduced a fault in the system and therefore you know withought doubt it is now not working, if the ABS light illuminates then it can be assumed there was no fault with the ABS to begin with and if a fault still manifests itself it is most likely to be another system.

However if the light does not illuminate it can be assumed that someone has played silly buggers with the bulb, it is possible the bulb has blown but given that the life of a bulb is quite long and the light should only illuminate before the car is started this is unlikey.

It is probable that someone has removed or disconnected the bulb from the instrument cluster to pass MOT or to sell the car on with no fault.

The next step therefore is to remove the instument cluster and investigate why the bulb does not work. Once the bulb is operating properly return the relays back to the correct positions and return to Diagnosing The Type Of Problem.


Note
Due to the recent introduction of computerised MOT's it is becoming more common for the bodgers to wire the ABS bulb in series with the battery light or brake light or any other dash light that comes on when the key is in position 1, and goes off when the vehicle is started, this simply mimics the correct behaviour of the ABS light regardless of the operation of the ABS system.


ABS System Fault

Have you recently jump started your vehicle?

99% of the time if you have then the resultant current spike will have fried the voltage protection circuit. Both early and late ABS systems fitted to the E30 had voltage protection circuits however on early systems it is found in the silver relay next to the ABS ECU in the glovebox.

On the later ABS systems there are two relays, I have always replaced them in pairs (since if one is beyond its best it stands to reason the other of the same vintage will be too) however only one of them contains the voltage protection circuit. They can be opened and repaired too, normally if you open the relay the fault is clear as its usually a blown resistor however the case is difficult to dismantle and fit back together and as they are so cheap I normally replace them as a matter of course.

The later ABS relays are found on top of the ABS pump under a black plastic cover screwed down with one star nut. If you need help identifying the ABS pump you need more help than I can give you!


You haven't recently jump started your vehicle?


Fuse/Relay/Wiring

It may still be a relay/fuse problem, but it could also be the ABS pump or ABS ECU or wiring between (i.e. everything bar the sensors and sensor ralated wiring). If you cannot find any problem with wiring then the relays are the cheapest item to replace typically £4 or less from a breaker on Ebayor friendly Zoner including postage. The early ABS system will only accept an early silver relay and the late system only accepts the later two relays.


ABS ECU

Should that not prove to be the problem the next most common problem is a faulty ABS ECU fortunately these are also relatively cheap typically £10-£20, they plug in and out on a fixed loom and are located above the glove box compartment, accessible by removing the plastic sheet which forms the roof of the glovebox from within the glovebox, swapping ECUs is a 5 minute job.

Note
When ordering a ABS ECU they are coded with colour stickers on the top of the case, find out which colours yours is coded with first and order the exact same colour replacement.


ABS Pump

I have never ever been met with a faulty ABS pump but it is of course possible, and should the other procedures have not worked and you are 100% sure its not a wiring issue this would be the next place to check.

ABS Sensor Fault

Please Complete

Originally posted on www.gevans.info

--March109 21:03, 20 July 2008 (UTC)