Brake Failure Message + BCU connections loose

Magyar1125 · Post by **Magyar1125** » 02 Oct 2018, 07:18

Hi All,
I'm the dad of a 2004 XC70 with 242,000 miles on her. A year ago, I got the Brake Failure message on my dash. It would come and go. Then one day, all kinds of other messages came up. The car still ran, but poorly. I bit the bullet and undid the negative battery cable, removed the airbox, and grabbed the wire bundle leading into the BCU. I gave it a pull. I gave it a push. I gave it a tug. Then reconnected the battery cable. PROBLEM SOLVED! Nothing wrong for a year until I sold it to my daughter's boyfriend (I came with the deal) and it died on his first outing. Same issue. Tried the same fix. Nothing. Now the car will not start. Plenty of battery. I read somewhere that if the battery gets low enough, memory will fade from the ECU and the car will not start. Anybody got anything on this? My plan: remove the BCU and check the visible connections. The printed circuit board is, I believe, the issue with soldered connectors lifted from the board. I may try to open it up and re-solder. Nothing to lose. Or I may send to XemoDex for a rebuild. XemoDex flashes the unit to match the car. BUT WILL I STILL NEED TO GET THE MEMORY FLASHED AT THE DEALER?
It's never just one thing.......
Thanks. Jeff

Post by **abscate** » 02 Oct 2018, 07:34

The brake issue and the no start sound like two unrelated things.

When where the plugs and coils last changed?

Try a bit of starter fluid (ether) into the air box to see if you can isolate ignition from fuel delivery problem. The definitive way to diagnose this is with a fuel pressure gauge on the rail or a measurement in VIDA software ($100)

DOnt crank it for more than a few seconds unless you have a battery charger.

Post by **oragex** » 02 Oct 2018, 11:14

If you scratched your head how to undo that connector see here at 12:00 www.youtube.com/watch?v=jKcDOLIYR3A

As above, I feel the engine running issue and the brake message may not be connected.

Obviously a code reader may point in the right direction but may also give misleading pointers. Careful when interpreting the codes.

Myself I don't have Vida, so the way I would do with this scenario is go step by step, check things - rather that guess-replacing them
in this order: test the alternator (engine running) see if it gets a decent 13.7V, also check power wires and connections around the car. May undo and inspect the connector at the ABS module. Before sending the module to xemodex ($$$) try reading the codes. Some people even split open the module to resolder some points (check online). Junkyard is another option but not sure how compatible are these modules (look at least for similar year and STC or DSTC option). Your 2004 also may be affected by corroded CEM - google up. Finally your AWD was sensitive at the DEM (again google), quite easy to see if it's corroded or not - this guy can also be fixed by that company and can cause a non start condition.

Disconnect the battery at all time so you don't spend an extra $100 at the end

Magyar1125 · Post by **Magyar1125** » 02 Oct 2018, 14:51

I have a cheap code reader. All it shows now is PO600. Basically, it is telling me that the computers are not talking to each other...no surprise since they are connected serially! The PO600 code is where I read that if the juice in the battery get too low, memory will fade from the ECU and the CAR WILL NOT START UNTIL IT GOES TO THE DEALER. I am working on getting the BCU out. I know how to do it but one of the screws is rusty and stuck...hmmmm. I will check connections as suggested when I am successful. Engine will not start so difficult to do an alternator test without taking her out. I have given thought to splitting the BCU open and re-soldering. Corroded CEM??? Can you tell me more?Will look into CEM and DEM. Thanks!!!

Post by **oragex** » 02 Oct 2018, 14:57

I assume the battery checks fine ? A non start condition can be related to corroded DEM, I'd check it first, google up how to find it. I'd say google up about these things, do a 'volvo cem or dem corrosion' search there are many discussions and details

Magyar1125 · Post by **Magyar1125** » 02 Oct 2018, 19:19

Thanks, Oragex. I have found these already and viewed them. I can look at the CEM tomorrow. I am set to get the BCU out tomorrow morning. I have also viewed the videos which people going in and re-soldering the board. I might do that first and test it again...nothing to lose. I would be surprised if the CEM had an issue...but I was surprised when I watched the video and saw that one was caused by a leak from a drainage hose onto it. First things first. Something is telling the car: "Don't you start!" I need to find out what that is. And it all started with the BCU....

Magyar1125 · Post by **Magyar1125** » 02 Oct 2018, 19:20

and one more thing...battery is fine.

Post by **abscate** » 02 Oct 2018, 20:18

The 2004 CEM has a known heat soak issue , there are a couple of threads on it here

Post by **oragex** » 03 Oct 2018, 07:15

While there, it seems there is an epidemy of non start at this moment. Try also to crank then careful push the schrader valve on the fuel rail, see if there is fuel pressure - use something over the valve so it doesn't spit fuell in eyes.

Magyar1125 · Post by **Magyar1125** » 03 Oct 2018, 09:01

I will check EVERYTHING I possibly can. New fuel pump a few years ago...