Famous DSC/ABS/BRAKE Trifecta problem
 

I've been chasing DSC/ABS/BRAKE Trifecta problem and couldn't solve it still.
Wondering if I can get some insight from members.
I'm using PA Soft BMW scanner for diagnostics.

1. Originally I had following ABS codes
- Pressure Sensor, open circuit
- Temperature of the brakes overheated
After long search looked like the Bosch DSC III 5.7 is bad. So shipped it to BBA-Reman for repair.

2. Received repaired Bosch DSC from BBA-Reman, installed but Trifecta still persists. Read the code, and it's different codes this time.
- Wheel speed sensor rear right, open circuit
- Lateral acceleration Sensor, open circuit
- Temporary system deactivation
So for testing, I've un-plugged Lateral acceleration sensor which is located under center console.

3. Read the code again, and it shows following codes
- Lateral acceleration Sensor, open circuit
- Yaw rate Sensor, open circuit
- Temporary system deactivation
Notice Wheel speed sensor error is gone now? But there is new code for Yaw sensor. Wondering, isn't Lateral acceleration sensor and Yaw rate sensor the same thing?

4. So I purchased used Lateral acceleration sensor (with newer superseded part#), installed. But Trifecta still persists. Read the code again.
- Lateral acceleration Sensor, open circuit
- Yaw rate Sensor, open circuit
- Temporary system deactivation

At this point, I'm not sure where to go further. I guess I can try another Lateral acceleration senor, and/or new speed sensor, but don't want to keep dump money into it.

Any thoughts? helps?

Thanks.

You need a shop with autologic. Temporary system deactivation code is probably from being sent to BBA Reman when it was unplugged.

The last 2 codes are persistent but after you replaced lateral acceleration sensor the code is still there, only other thing I can think of is steering angle sensor maybe. Have you checked the wiring for breaks?

Haven't looked hard, but couldn't find any breaks in wiring.
Do you know if Lateral acceleration Sensor and Yaw rate Sensor are the same sensor?

Thanks.

When the "trifecta" started, was it solid, or intermittent?

Pretty sure they are the same. There's like 3 different names for the "yaw sensor."

Check this out....

http://www.bmwclub.lv/files/BMW_X5_D...ty_Control.pdf

It was solid.

That's what I thought. Maybe that I new sensor I've installed is newer superseded part#, causing the problem?

The same part# yaw sensor was used in e53, e46 xi, e39 rwd and e39 rwd, and the one I received is from e39 rwd. Wondering if that could cause the problem since it's from rwd although it's the same part#?

Doesnt the new steering angle sensor need to be coded/calibrated to the car?

Who said anything about a steering sensor?:)

A new "yaw sensor" does not need to be coded/calibrated to the car.

My bad i got the two confused

I asked if it was intermittent, because "usually" when it's intermittent, it's the ABS module. If it's solid, then it's a sensor. But I can be wrong.
However, if you removed the ABS, you need to do the following steps:

-removal and install should be done with the battery unhooked, as it can damage the ABS module. Reconnect battery.
-if it's a new ABS module, it should be coded to the car (I used SSS Progman)
-if it's a new or remanufactured ABS, the next step (for both cases) is to re-cablirate the following sensors (I used GT1/DIS 5.7):
Steering angle sensor
Rate of rotation sensor
Lateral acceleration sensor

When calibrating these 3 sensors, the front wheels & steering should be pointed in a as much as possible straight position. The car has to be on a level surface. Battery 100% & battery charger hooked to it.

Once you have done these steps, erase ALL codes, then go for a test drive and see if any errors return.

If you have a solid "trifecta" and your scanner tells you it's a wheel speed sensor, you need to test all 4 of them. The best way, is to take the ABS plug off, then test at the connectors (it's easier than to take the wheels off). The speed sensor readings should be around 7.5 ohm (+/- 0.2) one way & 4.5(+/- 0.2) ohm with reverse polarity. If one reads different by big amount (or "0"/ infinity) that sensor is toast. if you don't know the ABS pins layout, I can provide them to you.

If the wheel speed sensors test good, the next step is to check the pressure sensor (goes at the back of the whole ABS module - where the brake pipes are). You need a helper here. Ignition on, and the helper presses the brake pedal. With the pedal off, it should read "0"V or close. With brake pedal pressure applied, it should start reading between 0-5 volt. the "5" volt is at max brake pedal pressure - around 250 bar? So your voltmeter should not exceed that value.

if this test is a pass, then you are left with the rotation rate sensors, acceleration sensors and steering wheel sensor. These sensors I am not 100% sure how to test, but they should give you some error readings when you try to calibrate them, I would believe. Also the GT1 might point you in that direction - I am not sure, because I haven't encountered that issue on any of my cars.