Advanced BMW ABS hints and tips
ENGINE APPEARS TO MISFIRE OR STUMBLE INTERMITINTLY
MODELS AFFECTED: 5 Series(E34), 7 series(E32), 8 series(E31) all equipped with ACS.
FAULT: Under certain specific conditions an apparent engine misfire or bucking may occur. This is not
an engine misfire.
CAUSE: Short (less than 100 milliseconds) fuel injection cut-off, as a result of MSR (engine drag torque
control) regulation. This is a normal ASC function that may occur under these conditions:
-The vehicle is equipped with ASC
-Vehicle speed between 45 and 60 MPH
-A rough road surface (e.g. potholes, railroad tracks)
-Light throttle(accelerator pedal only depressed 1/8)
-ASC not switched off.
SOLUTION: Replace the ASC control unit. no further diagnosis of the ABS/ASC system should be
ABS WARNING LIGHT ON
ODELS AFFECTED: 3 series (E36) and Z3 produced up to 5/96
FAULT: The ABS warning lamp is on in the instrument cluster, and fault code 145 (pump inoperable)
stored in the ABS control module memory.
CAUSE: Faulty relays produced prior to may 1996.
SOLUTION: Use the DIS tester to confirm that fault code 145 is set in the ABS control unit. Work
through test instructions in DIS confirm that the fault is not caused by any other components. Then
replace the gray ABS pump motor relay, witch is located in the power distribution box, rear left side
of engine compartment.
MICROPROCESSOR CONTROLLED ABS(uC-ABS)STORES ERRONEOUS INTERNAL DEFECT FAULT
ODELS AFFECTED: 7series(E32)-vehicles produced 06/91 and later, equipped with M30 engine.
5 series (E34)-vehicles produced 9/91 and later.
FAULT: Increasing number of uC-ABS control units are being returned for showing internal defect during
troubleshooting and readout of the fault memory. In most cases the fault is erroneous.
CAUSE: If the ignition is switched on with the cap of the D100 diagnostic connector removed, the erroneous
fault can be set by a low voltage condition on the TTD lead to this control unit.
-Erase the fault in the uC-ABS fault memory, while the diagnostic module is still connected and the
ignition is switched on.
-Before disconnecting the diagnostic cable, switch off the ignition
-Reconnect the cap for the D100 diagnostic connector, then switch on
the ignition again.
-Do not replace control unit.
ASC AND/OR ABS WARNING LAMP ON
MODELS AFFECTED: 3 series (E 46), vehicles produced up to 9/98
FAULT: The ASC and/or ABS warning lamps are on, with fault code 31 or 41(rear wheel speed sensor) set
CAUSE: Faulty rear wheel speed sensor.
SOLUTION: Replace the wheel speed sensor with a sensor with production date 22/08 or later.
ASC LAMP ON, FAULT CODES
MODELS AFFECTED: E38(7 series), E39 (5 series) with M62, or M73 engine.
FAULT: The ASC lamp is on and no fault codes are stored. If the under hood diagnostic connector is
removed the ASC lamp goes off.
CAUSE: Incorrect under hood OBD cap fitted.
SOLUTION: Install correct OBD connector cap (part number 12 52 1 703 202).The part number is inscribed
into the OBD cap moulding
ABS WARNING LIGHT COMES ON
MODELS AFFECTED: All with ABS
FAULT: ABS warning light comes on intermittently. Normal troubleshooting procedures find no defect.
CAUSE: If cars have recently had two new tires, or snow tires put on. Sometimes when the car is driven
over 50 MPH.
SOLUTION: Check all four tires on the car, make sure they are the same brand, style, and size. Check if
any of the new tires have substantially more tread than the rest. These differences may cause enough
variance in rolling diameters to confuse the ABS control unit, which intern gives a false signal to the ABS
ABS WARNING LIGHT GLOWS
MODELS AFFECTED: 3 series (E 36)-vehicles produced 1/96 to 3/96 without ASC.
FAULT: On rare instances the ABS warning may glow slightly after other electrical consumers have been
switched on. No fault is stored in the ABS control module fault memory.
CAUSE: Hardware fault in the ABS control module.
SOLUTION: If this is encountered replace the ABS control module.
ABS, ASC, AND ASC+T MALFUNCTION
MODELS AFFECTED: All models equipped with ABS,ASC OR ASC+T
FAULT: Any of the ABS ASC and ASC+T systems inoperative, intermittently inoperative, or illuminating
the warning lamp.
CAUSE: All BMW'S with slip control systems use 4 wheel speed sensors which monitor each wheels
speed of rotation with a high accuracy. The system control unit uses this information to calculate a
vehicle speed. In this way it detects wheel speed variation. If the inputs vary from each other by a certain
amount, the control unit is not able to do the calculation reliably (plausibility fault) and takes its self
off-line as a safety precaution(fail-safe).This can be because the wheels and tires are non-approved parts
and therefore do not agree with the system.
SOLUTION: Make sure the vehicle is fitted with BMW approved wheels and tires. Then do further
diagnostic testing to check if fault is resolved.
EXCESSIVE NOISE FROM ENGINE COMPARTMENT AFTER FIRST STARTING OFF(ABS SELF TEST)
ODELS AFFECTED: 3 series (E 36)- four door models only
FAULT: A noise(described as a rattle, groan or growl) occurs only after the engine is started and the
vehicle is put into motion. The noise is heard in the first 30 feet and only last a second.
CAUSE: Most of the time the noise is from the pump activation portion of the ABS self-test.
SOLUTION: The self test noise cannot be eliminated, can only be reduced, and even then not in all cases.
One way is to install insulated brake lines (only on vehicles produced before 03/92).
ABS, ASC/DSC, ECM FAULTS
MODELS AFFECTED: E38(7 series)
FAULTS: The wire harness can get damaged. ABS, ASC/DSC ECM faults show:
- 66 wheel sensor signal supply voltage
- 67 intermittent interference
- 5,6,7 wheel speed (plausibility)
- 30 left rear wheel sensor
CAUSE: The sharp edges on the tilt sensor(NAG) bracket damage the wire. The leak diagnosis pump(LDP)
and the wire harness from the left rear wheel sensor is routed through the slot in the tilt sensor(NAG)
SOLUTION: Remove the tilt(NAG) sensor, located behind the wheel arch in the left side of the trunk. Tape
the sharp edges of the tilt sensor bracket with electrical tape to prevent further damage to the wire harness.
Repair the wire harness and reinstall the tilt sensor. Using the DIS tester clear the fault codes.
BREAK INDUCED STEERING VIBRATION
MODELS AFFECTED: E46 and four door models produced prior to 10/99.
FAULT: Steering vibration when breaking, usually in the 50 to 60 MPH range.
CAUSE: The front axle on some cars is extremely sensitive.
SOLUTION: Remove front brake rotors and pads, also replace steering coupling and torx bolts with new
parts. Make sure the front wheel assemblies are balanced before re-installing. If the vehicle has dampened
hydraulic lines they need to be removed and replaced with original lines.
TWITCH FELT IN STEERING WHEEL ON RAPID BRAKE APPLICATION
MODELS AFFECTED: E46 not equipped with DSC.
FAULT: When the steering wheel is held very lightly with one hand and the brakes given a quick tap, it
may twitch slightly once. There is no disruption of stability of the car and doesn't pull to either side.
CAUSE: Could be from having unequal amounts of toe-in on each front wheel or because of a very slight time
difference in the build up of pressure in each front brake caliper.
SOLUTION: If the alignment has been corrected, you can install a dampener to modify the brake pressure
build up curve.(If the vehicle is equipped with DSC a dampener can't be installed because it will affect the DSC
ABS REAR WHEEL SPEED SENSOR
MODELS AFFECTED: 3series (E36)- 1992 models
FAULT: After diagnosis of a ABS system using the BMW service tester the following faults may be set:
- 84 or 88 wheel speed sensor missing or defective, left rear/right rear.
- 100 or 104 wheel speed signal not plausible, left rear/right rear.
CAUSE: The ABS wheel speed sensor at either rear wheel have poor solder connections at the coil connections.
SOLUTION: The solder connections were improved in production from date code 0811(81st day 1991). If the
date code of the failed sensor is 0801 or lower, both rear wheel speed sensors need replacing.
ABS HYDRAULIC UNIT
MODELS AFFECTED: 1993 318 is, 1993 325is, 1994 345 ic.
FAULT: It's possible that during the assembly of the ABS hydraulic units of these vehicles, the six bolts which
fasten the bottom cover of the unit to the housing were not tightened properly.
SOLUTION: All affected vehicles(identified by the DCS inquiry) hydraulic units need to be checked by torquing
one bolt on the bottom cover to 15 Nm. If it turns the unit must be replaced.