"Brake Failure" P0571 and P0504 Topic is solved

[abscate]

Get a loupe ( that’s optics , not a disease or a wolf) and have a closeup look at the big pins. Look for cracking in the solder around the pins.

Don’t overthink the cause too much, it’s a 17 year old car and it is inventing new failure mechanisms yet to be uncovered by us here.

[Marcobrick]

Get a loupe ( that’s optics , not a disease or a wolf) and have a closeup look at the big pins. Look for cracking in the solder around the pins.

Funny you should say that. There is no solder in evidence around any of the pins!

I flowed solder around all the pins on the board last night. Problem persists! I’ll get the codes read at the dealers next week. Meantime I’m pricing up a new BCM. ($OUCH$)

[chrism]

The brake failure message appeared while driving home after having the brakes bled by his local mechanic.

Might the mechanic have accidentally introduced air into the system? Or might he have pushed the pedal to the floor repeatedly and possibly damaged the piston seal?

[Marcobrick]

Might the mechanic have accidentally introduced air into the system? Or might he have pushed the pedal to the floor repeatedly and possibly damaged the piston seal?

I doubt the seal is compromised . There would be something physically wrong with the brakes then, but apart from no ABS they work perfectly.

Air is the abs pump maybe but I don’t know if the computer could know that?

The ABS module (BCM) is under heavy suspicion if for no other reason than it’s been hacked open by a previous owner. Still need the codes read by VIDA.

[Marcobrick]

Ok, so this afternoon I got an “engine system service required” message. I plugged in my code reader and I had the P0571 and P0504 twice each... I can’t erase the first set but I can erase the second set. This left me with fully functioning ABS, trip computer and odometer!! For about 1 mile. Then the whole lot came back. I went into the auto parts store for some oil and when I restarted the car, all clear again. Another mile down the road, Christmas tree lights on the dash..you get the picture.
I think my soldering has done something, but since I suck at soldering I just haven’t got enough penetration. In truth I’m too scared to apply a lot of heat to a circuit board because it’s the first circuit board I’ve ever touched.

I might crack it open again, suck out my crap solder and have a do-over. I have a friend who’s into electronics, I’ll ask him for some guidance and maybe some better equipment.

Feeling like I’m confident its the abs module now!

[Marcobrick]

When I parked yesterday, there were no faults. This morning the warnings were there as soon as I turned the key. I removed the BCM and took it to my friend’s house. He tested all the circuits fron the connector pins and could find no faults. The BCM is now in the freezer to be tested later when cold.

[Marcobrick]

FAIL. Making it cold didn’t replicate any faults. My friend undid my handiwork and resoldered the pins nicely but now my problem is again permanent.
I did achieve one positive thing today, the engine compartment fuse box was not mounted correctly. It is now!

[chrism]

This morning I removed the brake pedal position sensor. I replaced it with one from an XC90 that had no ABS warnings. The problem has not gone away.

Is this the part you replaced?

http://i.ebayimg.com/images/i/230922126 ... -l1000.jpg

Also, have you considered the possible failure or misadjustment of the brake light switch on the pedal itself? One of the codes you're getting refers to a correlation problem between the Brake Position Sensor and the Brake Light Switch.

Do your brake lights work? Does the Cruise control engage and disengage properly?

[Marcobrick]

Brake lights function normally. Cruise is disabled. I suspect the lack of correlation must be because the BCM is not correctly receiving and/or reporting brake signals.

[Marcobrick]

Can someone tell me if the ECM and TCM get their speed signals from different sources? I ask because my speedometer works correctly, the transmission works fine, but I have no speed signal on my live data on my CAN OBD reader...