"Brake Failure" P0571 and P0504 Topic is solved

Marcobrick · Post by **Marcobrick** » 08 Mar 2019, 00:16

Hi all. I’ve been absent from the forum for a couple of years in the Volvoless wilderness. I’ve recently been reading topics on the XC90 as I was sure I was going to buy one. I did however buy a 2002 V70 T5 in a lovely electric blue colour. Naturally it comes with a few faults the most vexing of which is a brake system fault.

There are some great writeups on the site regarding various ABS faults. I cannot find any that match my symptoms exactly.

Here’s what I have:

Brake Failure stop safely on the information panel
Orange warning triangle
Red brake light
ABS light
Amber stability control light (My car does NOT have DSTC)
I have an odometer presentation but the mileage is not increasing
Dashed lines where my trip information should be.
The speedometer DOES work normally
The transmission IS behaving correctly
I have normal and reliable brake light function and shift lock function

I only have an Innova 3130 CAN OBD scan tool and it picks off P0571 brake switch citcuit A and P0504 brake switch A B correlation. I can clear the P0571 but it comes back.

Earlier today I disconnected the battery and unplugged and contact cleanered(I’m sure that’s a verb) the ecu connections and the brake pedal position sensor plugs. When I reconnected the battery, started the car and cleared the codes, i drove it for 200 meters with everything working and no lights. After shutting off and restarting they all came back.

If I unplug the brake pedal position sensor (on the booster) it changes nothing and no new codes appear.
Would I be wasting my time (and money) changing this sensor?

The other item of suspicion is the BCM but that’s even more money. In New Zealand we don’t have a lot of electronics repairers that take on this sort of work and those that do charge accordingly!

I don’t have access to VIDA unfortunately without going to the dealer and the local dealership are unhelpful thieves.

Suggestions please...

Post by **RickHaleParker** » 08 Mar 2019, 13:50

I would look for wiring defects first.

P0571 = Brake pedal position sensor. Either the Brake pedal position sensor or the wiring.

P0504 = ECM-510F Vehicle speed signal

Diagnostic trouble code (DTC) information

Condition
Diagnostic trouble code (DTC) ECM-510F (no signal) is stored if there is no communication between the ABS/brake control module (BCM) and the engine control module (ECM) or if the communication is distorted.An error message is sent to the engine control module (ECM) and diagnostic trouble code (DTC) ECM-510F (signal too high / too low) is stored in the engine control module (ECM). Diagnostic trouble codes (DTCs) for the vehicle speed sensor (VSS) signal are stored in the ABS / brake control module (BCM).

Substitute value
The vehicle speed signal from the ABS / brake control module (BCM) is set to 0 km/h

Possible source
Signal too high / low:

defective vehicle speed signal to the ABS / brake control module (BCM) A diagnostic trouble code (DTC) is stored in the ABS / brake control module (BCM).

Signal missing:

contact resistance in the Controller area network (CAN) terminals
open-circuit in one or both CAN cables
one or both signal cables short-circuited to ground, voltage or each other
defective ABS / brake control module (BCM)
defective engine control module (ECM).

Fault symptoms
Malfunction indicator lamp (MIL) lit.

Marcobrick · Post by **Marcobrick** » 08 Mar 2019, 16:58

Except that the speedometer works perfectly...

Marcobrick · Post by **Marcobrick** » 08 Mar 2019, 23:15

I removed the BCM today. It has been opened in the past. It’s different to the spare P2 bcm I have unfortunately, so I can’t play Swapsies. Presumably it has been re-soldered.

Also when I clear P0571, the P0504 disappears too. Went to the local Pick-a-part today. They have a V70 turbo but somebody has beaten me to the brake pedal position sensor!

Marcobrick · Post by **Marcobrick** » 11 Mar 2019, 00:00

I know this fault knocks out the cruise control, but does it also prevent torque converter lockup?
Brake pedal position sensor is on its way.

Post by **precopster** » 11 Mar 2019, 05:29

The brake pedal position sensor is essentially the same unit as fitted to the 850s and there was a write-up here on MVS on how to repair it. The casing is a little difficult to pry open but once done there is a small contact board at the top that needs to be re-soldered.

Marcobrick · Post by **Marcobrick** » 11 Mar 2019, 13:21

I found the write up. Thanks! Maybe I’ll give it a go later this week when I’m off work. I have nothing to lose I guess.

Marcobrick · Post by **Marcobrick** » 13 Mar 2019, 17:13

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. I then opened up the original (yep, it’s tricky and hard work while trying not to wreck it) I have cleaned the insides, re-tensioned the wipers and re flowed the solder on the board. I’m waiting for the sealant to cure and then I’ll swap it back in.

IF this is the part causing the problem, is there a special reset procedure to apply once a good(?) part is swapped in?

Marcobrick · Post by **Marcobrick** » 13 Mar 2019, 19:34

After refitting the original "repaired" brake pedal position sensor (no joy) I have removed the BCM and taken the lid off to see what someone did in there last time. I see no evidence of soldering but the pins look to have been bent slightly. I came across the pin bending trick on a UK volvo forum but it doesn't seem like a sound enough "repair" to me.

: IMG_0200.jpg (445.5 KiB) Viewed 10628 times

Does the inside of this look normal to any P2 experts out there? All my previous experience is with P80 cars and the insides of this one are a bit different.

Marcobrick · Post by **Marcobrick** » 14 Mar 2019, 21:58

The P.O has provided me with additional information. The brake failure message appeared while driving home after having the brakes bled by his local mechanic. I’m not sure how that can lead to a fault like this.