P0503 code and brake failure message

AussieTimmeh

Today my XC90 started displaying a Brake Failure - Stop Safely message along with some warning lights, roughly a couple of minutes after I left home. The tripmeter was dashed out and the odometer stopped incrementing. Cruise could be selected but would not engage. I naturally browned my pants a little but quickly figured out the brakes were still working.

I turned around and started driving home, and after a minute or so, everything disappeared back to normal. I kept driving home, and noted that cruise could be selected but not engaged still, even though there were no errors. The odometer and trip meter returned to normal. I returned home to get the code reader and put it on the car, but when I restarted the car, the message had changed to Engine System Service Required with different warning lights. The car still drove fine around the driveway and cruise could still be selected, but not engaged. The odometer and trip meter were still working.

I drove the car a few times afterwards once I had confidence that it was safe enough, and found that the car randomly switched between these three states: 'Brake Failure Stop Safely', no failure, 'Engine System Service Required'.

In all 3 states, the car seems to drive fine. I've read stories of the tacho not working, the gearbox not shifting, the throttle not changing the revs with similar failures, but I don't get any of that. The only thing that is consistently not working now is being able to select cruise. I thought a sticking brake pedal might cause Cruise to not be able to be selected. My brother was driving behind me and reported that the brake lights are working fine, but I think that some pedals may have multiple switches, one for cruise and one for brakes. I could be wrong though.

I've done a lot of googling and read in a variety of Volvo forums that it could be a speed sensor on the wheel, or perhaps a module like the ABS module or BCM. Other people suggested dry solder joints, some say pedal sensor. One thread suggested a plug into the CEM comes loose.

I'd like to know where the vehicle gets its speed signal from, because that seems to be working fine at all times (speedo), so why does the odometer stop working I wonder? I was wondering if anyone had any experience with this and could offer any suggestions before I start down the path of replacing things?

AussieTimmeh

Bit of an update. Had the error so I swung by my local mechanic this morning and ran the G-Scan over the car. It came up with the following fault that seemed relevant: Communication with the ABS control module. Signal missing.

I'm not sure if it's the ABS module not communicating with a single sensor, or the car not communicating with the ABS module. This site would indicate it is a problem with the module itself: https://www.dtcdecode.com/Volvo/CEM-1A5F

I'll have to do some more searching to see if there are any ABS module connectors that could be cleaned or reseated, otherwise I'll have to start looking for a new module. If anyone recommends a place that sells them, I'd appreciate any advice.

pauljloz

Did you check your battery condition first?

AussieTimmeh

pauljloz
Did you check your battery condition first?

I haven't, no. I did replace it last year when I had starter motor issues, so it should be pretty good, but I can check it again. Is there a good way of checking them at home, or should I take it to the mechanics to have them check it? I have a multimeter but not sure if I should be checking while off, cranking, or idle.

AussieTimmeh

Bit of an update. Still happening occasionally but only on hot days, roughly 30+ degrees C days. Will occur about 2 minutes or so after I start driving if it's a hot day. Also once the codes are cleared, a power cycle fixes the cruise issue and it will work again until the next time. On cooler days, the car is fine like nothing is wrong. Still unsure what to change first at the risk of wasting a lot of money. Mechanic tested the battery ok.

VolvoDeger

first of all you need a wiring diagram and see when it happens if 12 volts is being supplied to bcm and a good earth. then i would be checking the can wires from bcm.

AussieTimmeh

VolvoDeger
first of all you need a wiring diagram and see when it happens if 12 volts is being supplied to bcm and a good earth. then i would be checking the can wires from bcm.

Ok thanks, I'll see what I can find.

AussieTimmeh

For anyone else who may have this in the future, the fix was having the ABS module refurbished.

jamesinc

AussieTimmeh
For anyone else who may have this in the future, the fix was having the ABS module refurbished.

This seems to be a pretty common occurrence with older ABS Volvos, what year is your XC90?

Thanks also for reporting the outcome ?

AussieTimmeh

jamesinc
https://ozvolvo.org/discussion/comment/188641#Comment_188641
This seems to be a pretty common occurrence with older ABS Volvos, what year is your XC90?
Thanks also for reporting the outcome ?

No worries. 2006. My local Volvo specialist that fixed it said it's very common. My ABS module was so bad that it was deemed unrepairable. They had to buy a second hand one and have it refurbished and coded to my car. They said it was very common, as you say. A new module was something like $3800 from Volvo (from memory), second hand unit was $250 and refurbishment/re-coding was around $1200 so still better off, and comes with 12 months warranty (for what its worth).