ABS warning light

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ABS warning light

Postby MickZ3 » Sun 14 May, 2017 13:55

I’ve owned a BMW Z3 for about ten years, it only comes out during the summer, so its only done 60,000 since new. It’s an E36 with a 1.9 M44 engine, it was manufactured May 1998. Last autumn the ABS warning light came on and went out again, this repeated a few times. The car was put away for the winter and was bought out for the summer and I serviced the car as usual for the summer. The ABS warning light came on again and went off after a few miles, this repeated over a number of days.

This Z3 does not have a 16 pin ODB11 connector in the driver’s footwell, it only has the 20 pin connector under the bonnet. I have a cheap code reader but it does not access the ABS system so I decided to clean or replace the front wheel sensors as a first step, as the Bosch sensors are only £24.00 each.

The service manual says remove the retaining screw and remove the sensor, they don’t move, looking at a new one they are an interference fit in the bore hole. With a very small chisel, 1/8 inch, I chipped away the body of the sensor to reveal the copper screening mesh, this mesh was then pulled out so that body size could be reduced. The body was then cut so that the end of the sensor was intact but separated from the body. Then on the cable side the sensor was chopped off. The remains of the sensor in the backplate was then drilled several times with a 2.5mm drill around the edge of the sensor. Enough of the material was removed so that the sensor could be punched out using a small pin punch. The new sensor could then be fitted.

Repeated the process on the other front wheel sensor. All seemed good for a couple of days, then the ABS warning light came on and stayed on.

Decided that a code reader that communicated with the ABS system was needed, decided to purchase a Autel Autolink AL619 http://www.auteltech.com/ and a conversion cable for the 20pin to 16 pin OBD11 connector. The code reader worked and gave the code as 71 which is ABS pump failure. Did a few checks with a multimeter to make sure the ABS was powered correctly and all fuses were good. Although the code was for pump failure, was it the controller or the valve block which was faulty. I did not want to fit a second hand unit from a scrap yard so I found that Ecutesting http://www.ecutesting.com/ would test and recondition the unit if faulty.

Sent off the controller and valve block as one unit and it was returned in three days, they confirmed it was faulty and they had repaired the unit.

Refitted the unit and bled the brakes using a pressure tank, in the sequence, rear right hand side, rear left hand side, front right hand side, front left hand side. Open the bleed valve and let the fluid run out until it is bubble free.

No leaks but the brake pedal felt spongy so tried bleeding the brakes again with a jumper between, pin 30 and 87 of the pump relay socket. No improvement! This method does not work with the ABS system on this car, there are two valves per calliper, and the valves need to be opened to get the air out, running the pump with a jumper does not do this.

Turned the ignition on and the ABS light went out, so the repair was successful, but the brake pedal felt spongy.

The BMW manual say bleed the brakes again with the valves open.

To open the valves I used INPA on a laptop, purchased the USB to serial converter and the 16 PIN ODB11 to round 20 plug.

The method used for each wheel was, in the order, rear right hand side, rear left hand side, front right hand side, front left hand side.

Have the pressure tank connected and the system pressurised.
Open the input and exhaust valve for the wheel using INPA.
Whilst the ABS valves for the caliper are open, pump the brake pedal a few times and apply pressure on the brake pedal.
Crack the bleed valve open and the air is expelled, the brake pedal drops to the floor keep the brake pedal depressed.
Shut the bleed valve.
Release the brake pedal.

Repeat for each wheel.


A few tips which may help if anyone else does this job.

Use a syringe to remove the brake fluid from the master cylinder.

When you remove the brake lines from the valve block, slip a plastic pipe over the ends so that the fluid can drain into a container, I used an icecream tub. It prevents the fluid being dumped on the floor.

There is not a lot of room to use a spanner on the brake lines, I used a ratchet flare nut spanner and crow’s foot spanners to remove and replace the brake lines. There are two sizes of flare nuts, 11mm and 12mm.

The electrical connector for the controller is unusual, lifting the top handle causes the pins in the plug to be pulled out of the socket. It doe take some force to lift the top handle. When the connector is refitted align the connector and slowly push down on the handle, this cause the plug and socket connect.

Ring spanners are need to open the bleed valves, the bleed valves on the rear wheels are 7mm and the bleed valves on the front are 9mm.

A pressure bleeder made the job simple, I used a pump up type.

A few photos are attached to show some of the points.

Hope this helps anyone else doing the job!

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MickZ3
 
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  Z3 roadster 1.9

Re: ABS warning light

Postby gookah » Sun 14 May, 2017 21:00

how come you removed the hydraulic pump?
the abs ECU just unbolts with 4 bolts with no loss of fluid or need to bleed the brakes? the fault is normally just a dry joint with the eco
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I have an element of 'M-styling' on my car, If that's a good enough reason for the manufacturers to adorn a 320 with the M badge, then its certainly a good enough reason for me..
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