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M635uk

Abs issue 535i se

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Hi, my ABS will not engage under heavy braking.

 

So ABS seems fine on engine start up, ABS light comes on, then goes out as it should.  However when under heavy braking  i can get one or both front wheels to lock up, but the ABS will not engage...ABS light does not come on when this happens.

 

So no ABS, but the module will not throw up a fault.

 

Any ideas?  Air in the system?

thanks

Edited by M635uk

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Well I bled all the calipers today so definitely no air in the system.  Still get lock up without the ABS doing it’s stuff.  So seems to be more of a control problem.

Edited by M635uk

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How are the ABS sensors? Are they working correctly? But if both wheels are locking then what is the likelihood of both sensors being faulty at the same time.

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I would have thought that if there were sensor issues then it would detect one or more wheels speeds incorrectly and go into fault mode.  That’s what it did on my old m635 which is essentially the same system.  I can check for a pulse output when spinning the wheel to be sure it is actually generating a signal.  I could also disconnect one the sensors and see if that makes the system fault.  It should do.  Thanks.

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Yeah I did think that as I typed. But at least it is one less thing to check. Seems like the wiring and sensor system is good, is there anything else in the abs system left to check apart from the ABS pump? 

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I've not had problems with E34 ABS but I was more familiar with my E39 when it had problems. I found a wealth of info on the US forum bimmerfest.com like walkthroughs on ABS issues. 

 

An example being here. While this is E39 info I think a lot of the issues will be shared. Worth educating yourself with.

 

Keliuss

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Found somewhere that rebuild abs modules ecutesting.com I have used them before for an ecu on a 6 series, but before I send off I had one question.

 

Does the abs take an input from brake light switch so it knows the car is actually braking?  If so this is the only thing I can think of that would cause the ABS to not operate and not throw up a fault?  Any thoughts.  Thanks 

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Yes, the brake light switch is linked to the ABS ECU at terminal 25. There are two ABS relays, one is a six pin main relay plus a four pin relay for the ABS pump. The main relay is in the plastic E box with the engine (DME) and ABS ECU's and it's the white one. The pump relay is on the pump itself under the black plastic cover with ABS on it.

 

Be aware that the ABS is different on 535i's with traction control and fly by wire throttle. 

 

Also, having the drivers side ABS sensor cable too close to the coil lead can make them go funny. It picks up ignition signals but it normally brings the ABS light on. 

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4 minutes ago, Sir Anthony Regents-Park said:

Do the brake lights and cruise control work? 

No cruise control on mine, brake light switch failed and was replaced a few weeks ago and were working, but I need to double check now and also that the ecu gets the signal on pin 25.   I am remote from the car so will have to check at the weekend.

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