E53 2003 X5 4.4i ABS/DSC/Brake with Transmission Issues

[XeroPhane]

Hello Everyone,


I hope it's okay starting a new thread on this.


For some months, I have been chasing the ABS+DSC+Brake intermittent amber lights issue, two days ago, my transmission has entered failsafe. I have a feeling they're linked but I definitely need help in pinpointing the issue.


The ABS/DSC codes that re-appear after clearing memory are:
#105 - brake pedal switch signal
#115 - pressure sensor signal interference.


A couple on the ABS/DSC/Brake issue: My power steering reservoir and coolant reservoir have both had leaks right onto the main connector. I've recently dried and cleaned the connector, as well as applied dielectric grease into each hole. Also it sounds like my U joint or something in the neighborhood is wearing out. About once a day, when the 3 lights come on, and the rear brakes will completely lock up. It doesn't put the vehicle to a screeching halt but instead creates a pretty severe brake drag that I need to pull over or else the rotors heat up red. The only way to release the brakes is to open the bleeder briefly, they spray the excess pressure, and system functions normally (albeit lights stay on). I've just replaced those rear rotors, brake pads and both brake wear sensors. I have also bled the brakes using INPA a number of time. Since the issue persists, I'm basically facing the need to re-bleed and replace pads too frequently. The condition under which the brakes lock up is pretty inconsistent too.


I took 3 videos of the live view analog behavior in INPA (links below). In summary, initially the pressure spiked briefly to >200, the lights came on and the pressure quickly subsided. Without pressing the pedal the pressure and the brake light switch values would fluctuate around 1 unit each (+/-1 for pressure, +/-0.1 for brake light switch). When pressing the pedal, the values would raise as normal, except the brake light switch was "!12.1" and the pressure would fluctuate around 48. Without pressure again a few seconds later, the pressure spiked to 291 and held that value for about a minute, after which it went back to its "normal" ~48 range.


The ABS/DSC suspects (in my mind) are:
* master cylinder
* brake light switch
* speed sensors
* ABS control module
* DSC pressure sensor


Recorded INPA behavior videos:
Part 1 of 3
Part 2 of 3
Part 3 of 3


And now we have the transmission failsafe mode...
My X5 has an automatic transmission.
Two days ago on the way into work, I did notice the higher pitched sound that usually occurs at lower speeds and RPMs, along with the deeper rumble that occurs at higher speeds and RPMs were both audible the entire drive. Otherwise, operation felt very normal (albeit trifecta lights did come after about 10 minutes driving). When we got over the pass and I came to a stop, as I slowed to nearly a stop, the vehicle jerked to a stop. The vehicle was a bit jerky in small bursts while idling. I put the car in Park, and the jerkiness stopped altogether. Then again putting into gear and taking off was also very jerky. We didn't get far until the RPMs and transmission didn't coincide and the vehicle entered Transmission Failsafe Prog. with OBD2 P0721 code. I pulled over, turned off the car, waited, restarted, cleared the codes, and I was able to drive to a safe spot nearby. The X5 jerked to a stop, and has since been unwilling to shift into any gear (reverse or drive).


The two codes that persist are:
OBD2: P0721 Output Speed Sensor Range/Performance


INPA: transmission: 59 Festbremsdrehzahl ("stall speed")


Last night, I checked the transmission fluid condition and level, and that checked out. Honestly, I don't know where to start in terms of diagnosing this. I unplugged the ABS control module harness as a test but the transmission failsafe issue remained. The turbine and engine speeds were consistently around 576 rpm, and the output speed remained fixed at 0 rpm. When I put the shifter into gear (which is relatively stiff now) the X5 will eventually make a loud whining sound toward the front of the transmission.


In summary, the symptoms are:
ASB/DSC/BRAKE trifecta with rear brake drag
DSC codes:
#105 - brake pedal switch signal
#115 - pressure sensor signal interference.


Transmission failsafe with turbine/pump/? whining sound while shifter in Drive. Transmission will not shift into gear.
Transmission codes:
OBD2: P0721 Output Speed Sensor Range/Performance
INPA: transmission: 59 Festbremsdrehzahl ("stall speed")


Thank you in advance for any advice!

[dirkgently540]

hey there,
Just experienced the exact same situation with my '02 4.6is. The warning lights have been coming on intermittently, however today was the first time the rear brake locked. Freaked me out.

My first thought is my battery is pretty bad. Drains overnight. It's a new battery, been replaced under warranty already, so I thought I might just keep charging it overnight and see if it gets better in warmer weather. I know that bad batteries will cause all sorts of weird malfunctions in e53's.

Now I'm starting to think that the low voltage, or amperage or whatever, is causing modules to act up. Maybe the brake module is malfunctioning? Weird that it is capable of actually locking a caliber, though. That seems pretty unsafe, allowing the module the ability to lock a caliber is disconcerting, especially when your driving at speed.

How'd things work out for you?

[jclausen]

Did you replace the brake light switch yet