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Monday, 10 February 2014

Last little issue with my 1998 BMW E36 Touring - ABS Pump

DIY - ABS Hyraulic Unit Repair - BMW M3 (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X):

'via Blog this'

I needed some wheels a few months ago so I took a chance on a 1998 BMW E36 (3 series) Estate. I bought the car for £500 so did expect a few issues. Here is what has been replaced so far:

1. Brake pads

2. Brake pad sensors

3. Back shocks and 1 collapsed coil

4. Back wiper unit and control unit (still not working :-( )

5. ABS sensors, front and back

The ABS light is still on and I took it to a "guy" to reset the diagnostic code after the sensors were replaced. Unfortunately it seems to be the ABS Pump at fault.

It seems this is a known issue so I will fix it myself when the rain and sleet stops in the UK.

Here are three articles I found.

1. Remove the ABS pump (hydro unit)

Disconnect the negative battery terminal. Sukc out as much of the brake fluid as you can from the fluid resevoir (a turkey baster works nicely). The pump is located beneath the master cyclinder. You'll have to remove your MAF from the throttle body. It is NOT necessary to remove the brake resevoir or master cylinder. It is a good idea to label all the lines so you know where everthing goes when you reassemble.

You may run into problems removing the hose clamps from the connections to the fluid resevoir. This is actually the hardest part of the whole DIY. BMW uses those lovely single-use sacrificial crimp clamps. You will have to cut them off with your Dremel. DO THIS VERY SLOWLY AND CAREFULLY, or you will be buying a new fluid resevoir. Also be sure you have some replacement screw-type hose clamps ready for when you reassemble (unless you are masochistic and want to intall new BMW crimp clamps).

2. Remove pump (continued)

The pump is held in place by a single bolted rubber stopper in the front of the unit. There are two more stoppers in the aft of the pump which fit into two retaining cups. Loosen the front nut and tilt the front upwards, and pull the whole thing out.

Warning: Be prepared for fluid spillage.

3. Remove bottom plate

Marvel at your solenoids.

4. Test electrical connections

Refer to wiring diagram below. The diagram on the right (from Bentley) is only for 1995-96 without AST. The Table on the left is compiled from the Teves Mk IV manual.

From the Teves Mk IV manual that you downloaded, you can determine the expected resistances across the various valves. All the testing will be done at the 12-pin connector on the pump. You should be able to verify the faulty valve from your diagnostic sheet.


5. Remove filament wire

Un-solder the filament wire. THIS THIN FILAMENT is the culprit. With age it sometimes cracks or tears or corrodes. Don't bother trying to find the break in the circuit, it is virtually impossible to see. Just remove the whole thing.

6. Gasket seal

Before reattaching the harness to the hydro, put a bead of gasket sealant on the edge where the harness mates with the pump body.

7. Rewire the valves

Here is the path for my particular unit. This isn't an exact tracing of the filament. I had to go the long way for some wires (for example, T to A to D to E to B ).

Rewiring in progress

 Commentary: After doing this little exercise, I realize why BMW went with filament wire instead of full-on gauged wires: filament is easier to install. The entire circuit is pre-printed & mass produced on the conductor film; all the assembler has to do is sauder all the pins in order, much faster on an assembly line. No need to route individual wires. The drawback is that the filament eventually corrodes or disintegrates, causing a fault.

8. Verify your wiring

Once you are done wiring, re-test the resistances at the pins using the table in step 4 above. If you did everything right, the readings should now be within spec.

ABS Pump Rewire

This is how I rewired my ABS pump in my 1996 BMW 328i

Remove the pump by taking off the 5 or 6 fluid lines, disconnecting the electrical connector, and removing that one nut at the front end of the pump assembly.  Takes about 10 minutes to remove.  It might be easier if you remove any little bits that are hovering above the pump assembly.  I took off the MAF and air tube and moved some other stuff around to make it easier.

Once it is off, take it to your bench and CAREFULLY clamp it in a vise or otherwise position it in a stable manner so that you can remove the plate on the bottom.  There are 6 torx headed bolts that you remove to get to this area of the pump.

This is what it looks like at first:

Note all the corroded flexi-cable.

Here is what it looks like after you carefully desolder and remove all the flexicable and rewire it:

Here is a wiring diagram I drew up.

All the solenoids share a common contact, and these are all tied back to pins 2 and 7 on the connector.  Notice that pins 2 and 7 on the connector are also common.  I numbered these myself and these numbers mean nothing and do not relate to any numbers you may find on the connector.

I started at the right side of the connector from the perspective that my pictures were taken and numbered it from right to left.  I did this also because the wires come into that connector from the right.

I have no idea what gauge of wire to use.  I am obsessive, so I went bigger than I am sure you really need to.  To do it over again, I would buy a good grade silicone insulated wire so that you wouldn't have so much trouble melting the insulation during the soldering job.  We used 16 gauge, but I bet 18 gauge would be easier to work with and still meet operating expectations as well.

I bled the brakes normally starting at the farthest wheel and working my way in.  The normal way, having someone pump then hold the brakes while I cracked the nipples.  I went ahead and bled them until the fluid was clear so effectively changing the fluid, but I don't think you HAVE to do it that way.  Lots of people talk about shorting the relay to activate the pump during bleeding, but I didn't do it, and I have used the ABS several times after this repair and it is working fine and I still have normal brake pedal feel and pressure.

My ABS light went right off after we were done bleeding the brakes and started the engine.

Hope this helps you and good luck in your repair!


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The definitive guide to self diagnosing your ABS/ASC light.

Look familiar?

If you're like me, one of your biggest pet peeves is a Christmas tree dash. Some people don't mind trouble lights on; I am not one of those. I cant stand the feeling that something is wrong with my car.

A BMW dealer will quote you anywhere between 1-2 hours of diagnoses charges (@ ~$120.00/hr) to read your ABS/ASC faults for you. If you are all about saving money, and learning something at the same time, you may find this useful. I will show you how to find the faults in your ABS/ASC system using a simple multimeter without being at the mercy of the dealer.

To start off, download the proper ETM for the year of your vehicle from TIS online. In this you will find the proper pin out info for your year. Use this link:

Change the year in the above link to match your vehicle. Example: if you are working on a '99 change it to: ""

You will need to remove your glovebox to access your ABS/ASC computer connector. Here they are:



Here is how the pin numbers are laid out in the connector:

I ignored the assignments off to the left, they're wrong as far as my '97 was concerned. Use the ETM you downloaded for the proper pin assignments for your vehicle.

For a '97 we refer to the following assignments for reference:

Some of the most common things that will cause an ABS fault in your system are amongst the following:

1. A faulty wheel speed sensor
2. A bad ABS relay
3. A bad pedal travel sensor
4. A stuck/clogged solenoid valve
5. A faulty ABS pump motor
6. A bad brake light switch

Testing your wheel speed sensors.

Perform all of these tests with the ignition in position 3.

Our cars use Variable Reluctance type wheel speed sensors. In the tip of the WSS is a magnet and a coil that produces an AC voltage proportionate to the rotational speed of the wheel. This signal is sent to your ABS computer where it uses it to monitor the speed of your wheel rotation to decide when to activate/deactivate the ABS solenoids.

Test the sensor for proper resistance:

The specification for resistance of the sensors per BMW is between .5 -2 Ohms. Test this by identifying the proper pins in your connector that apply to that sensor. Let's use the rear Right for example. Using the above pinouts we see that pins 10, 45 are the 2 pins for the sensor. To measure the resistance over the WSS, apply your black multimeter probe to pin 10 and the red on pin 45. With your multimeter set on ohms you will get a reading. Do this on all 4 sensors. If the sensor is out of spec for resistance, replace it.

Test the sensor for proper function:

With your multimeter set to read AC volts, remove the wheel, then unplug the sensor from the harness. Probe the + pin in the connector on the harness side with red, and the ground pin with the black and spin the wheel. You should see your voltage produced increase with speed of the rotating wheel. Do this for all 4 sensors. If the voltage is not consistent with wheel speed replace the sensor.

Verify proper power supply to the ABS computer.

The ABS computer gets numerous 12V inputs from different areas all pretty much through the ABS relays/fuses. Using your multimeter set to DC volts, connect your black probe to pin #1 on your connector and leave it there while you perform the following tests. Referring again to the above pinouts, we see that we should have a 12V supply to the ABS/ASC computer at pins: 3,16,33,35,51 with the ignition in pos. 3. Using your red multimeter probe, touch all of these (may be different for your year) pins and verify that there is voltage there. If there is not, you have a bad power protection relay (stuck open) and/or fuses, and your ABS computer is not getting power. Make sure that your ABS computer is getting power by checking all the necessary pins for 12V. Your actual voltage will vary but it should be close to the measured static voltage of your battery which is close to 12V but could be as low as 11 or more in some cases depending on your battery. A voltage below 7 volts will trigger a fault code and turn your ABS/ASC light(s) on.

Test your ABS power protection relay.

Your abs power protection relay is an internally fused relay that is designed to blow and open when subjected to over voltage protecting your ABS computer from damage. If the relay is bad you will not have any power at the pinouts outlined above in the 12V power tests. If you do not have power in the previous test at the specified pins, this relay has tripped. If this is the case, remove the relay, and test the pins again; you should have full power everywhere with the relay removed. If you have power again after removing the relay; replace it.

Here it is:

Some more in depth testing info:

The way this relay works is; when power is applied over pins 85, and 86 you energize the coil magnet and it closes the relay. The closing of the relay is what completes the circuit and allows current to flow through it.

Make sure the diode in the relay works. A diode is a one way valve for electricity; only letting it flow one direction. Put your multimeter on resistance. Put the red terminal on pin 30a, and the black on 30. You should see a resistance reading between 50-100 Ohms. Now reverse your probes, putting the black probe on pole 30a and red on 30, you should now see infinite resistance. If neither of the above cases is false, the diode is bad and warrants replacing the relay entirely.

Test the continuity of the inner circuitry. Before energizing the relay, put your multimeter on continuity test. Red on pin 30 and black on 87a, you should register contact and hear a beep and/or signal that your multimeter makes to signal continuity.

Power up your relay by adding 12v across pins 85/86. you should hear a click. If so, the circuits are closed. Verify that they work by testing again for continuity, this time red on 87, black on 30. 87a no longer applies when energized because it becomes disconnected when the relay closes.

Test your ABS pump inlet/outlet solenoids.

Do this with your ignition in pos. 3. Our ABS systems are 4 circuit systems. Each hydraulic circuit to each wheel has 2 solenoids. 1 to modulate inlet pressure and 1 to modulate outlet pressure. Referring to your proper pin out, select which valve you want to test. Example, lets pick the inlet valve from the rear right. According to the above pinout, the pin to control it is pin #39. Set your multimeter to measure resistance. Connect your black probe to ground (pin 1 or any other ground pin) and the red one to pin 39. Specs for resistance for the valves are:

Inlet: 2-9 Ohms
Outlet: 2-7 Ohms

anything out of spec is likely a stock/clogged solenoid and would warrant a replacement abs pump.

Test your brake light switch

With multimeter set on DC volts, probe pin 1 with black, and 32 with red. Push your brake pedal. With the brake pedal pushed, you should have 11+ volts displayed. With the pedal at rest with no pressure you should have 0 volts.

Test your hydro pump motor for operation.

Do this with accy pos. 3 on. Measure the resistance between the 2 ABS pump sensor signals; pins 49, 50 in this case. BMW spec is 10-40 Ohms for the connection. Out of spec means new ABS unit. Within spec = continue reading. If resistance checks out, go to your fuse box and pull your abs pump motor relay. Its the 5 pole relay, not 6 pole. Jump the always hot pole to your pump supply line. (ID this by looking at the diagram on the side of the relay.) You should hear the pump start up, if not, its nad.

More to come

1 comment :

  1. This is easily one of the best DIY articles I have come across in quite a while! (The proper use of the English language is a bonus - it gives insight into Ray Davies' meticulous attention to detail which is typically a requirement for the task at hand...). Ray, if you are monitoring this thread, I am busy upgrading my '95 E36 (M43) to include a CCM (Check-Control-Modue). Would you happend to have any wiring diagrams required between the CCM and the rear brake clusters? I have an article that allows for the upgrade of the cluster pinouts and breaking the circuit between the two bulbs. I do not know however where the extra two wires from the cluster, are supposed to go to... Here's hoping :-) Conrad from JHB, South Africa


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