ABS/DSC Trifecta questions

[ancho]

2001 740i Sport.

Had the Trifecta lights pop up about a month ago. Cruise control was intermittently functional, speedometer was OK.
Did the diode testing of all 4 sensors via the large connector in the engine compartment - all tested OK - values all very similar.
Sent the ABS module to BBA for rebuilding, received it back today, disconnected battery, reinstalled module.
Trifecta lights off initially. All came right back on seconds into the first drive.
Plugged in my scantool, both front wheel speed sensors reading 0 while rears reading correctly. Left front sensor at one point did have a reading but I'm not sure if it was accurate.
Error codes present for both front wheel speed sensors delivering implausible result.
Also had an error code for an EGS module not communicating.

I cleared the codes, to see what would happen. Bad idea.
This made the car undriveable - DSC light flashing, no throttle response - car wouldn't move.
DIsconnected the newly "rebuilt" ABS module, now the car is perfectly driveable again (aside from the cruise/speedo/odo not working).

I called BBA, they are going to re-inspect the module. Anything else this can be besides the ABS module?

Edit: BBA says they ran through their testing on the module again - could not find any fault in it.

9/5/17 update, received module back from BBA, after it passed all their tests.
Reinstalled in car.
No trifecta lights illuminated on first startup. Drove forward and back a few feet, no lights.
Plugged in scan tool, lights came on again, then went off. Then back on again.

Codes currently showing up in the ABS/DSC module:
52 - DSC rotation rate sensor
53 - Lateral acceleration sensor
5B - No message from steering angle sensor control module.

AND, rear wheel speed sensors read correctly, front left intermittently will show a reading but different from rears, but front right shows 0 all the time.

I have a brand new module on the way from FCP so I am hoping that this random assortment of problems is an indication that the module is hosed.

[oldroller]

Hi Ancho, curious to know if you ran scantool on the wheel sensors prior to sending out the module.

My '01 has had increasingly aggravating issues, which began as the trifecta after 30 mph, but no other symptoms. Tim's site fixed that per this, temporarily...
http://www.meeknet.co.uk/e38/ABS/Index.htm

Precharge pump cured the 30 mph lights. Then I began to have light issues along with cruise dropout. It would engage, hold for a while then surge and disengage totally,
with no reset.

I ran diagnostics on the wheel speed sensors, all read good and produced a good sine wave at rolling speed. After reconnecting I had no issues for a couple weeks. Then, on backing up out of
the drive, I experienced ABS activation, in reverse!
Thereafter I have slow rolling braking ABS, sometimes in reverse, cruise dropout, and the trifecta coming on at 25-30 mph when they are off initially. The module seems to be the only common
denominator for these issues.

From what I understand, all wheel speed inputs go directly to the module then out to their respective circuits/controls/etc. If all harnesses and connections are 100%, as well as sensors, the module
is the culprit. I have read that rust, dirt can build up in the area of the sensor reluctor wheel and cause issues, also.

It might be worth pulling the front sensors and checking for debris, especially since you experienced scan readings off in regards to the front wheels.

Interested in what you find.

[ancho]

Unfortunately, I did not use the scantool prior to sending out the module.

I had already cleaned up the RF wheel sensor prior to sending out the module, but not the LF.

Today, I used the scantool to view the EGS (transmission control module) data, and it read all 4 wheel speeds as being the same, and correct. So I am taking this to mean that the EGS is still capable of receiving wheel speed sensor inputs despite the ABS module being absent, and furthermore, the sensors and their wiring are functioning properly.

[psjr]

Are you saying the wheel speeds are showing up in the EGS while the DSC module is still unplugged?
As you saw in your diode testing, the wheel speed sensor wiring goes directly to the plug for the DSC module, so if it is unplugged, the wheel speed sensor data is not getting anywhere.

[ancho]

Are you saying the wheel speeds are showing up in the EGS while the DSC module is still unplugged?
As you saw in your diode testing, the wheel speed sensor wiring goes directly to the plug for the DSC module, so if it is unplugged, the wheel speed sensor data is not getting anywhere.

Yes. The EGS is reporting wheel speeds despite the DSC module being absent from the car.

I am wondering if this is a calculation done by the EGS in the absence of it receiving true data from the DSC over the CANbus?

[ancho]

I've got a brand new ABS module on order. BBA told me that if I ordered a brand new module and it solves the problem they would refund their charges for "rebuild" or whatever they're calling the work on my old module.

[ancho]

updated original post with more info.

[ancho]

Final update - for anyone wondering.

New module installed, coded.
Performed steering wheel angle sensor calibration and end-of-belt test as required.
Trifecta lights still on, but only for both front wheel speed sensors reporting implausible values.
Replaced both front wheel speed sensors (despite them testing OK with the diode test published everywhere), with new VDO units.
Cleared codes, trifecta lights off for almost 100 miles now.