P38A BECM Perhaps?

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GavinDavis

GavinDavis

Member
Posts
40
Hi Guys,

Some of you may have seen a couple of my previous posts, whereby I recently changed the diesel injection pump on my 2000 DSE. All is now back together and running great mechanically, however I have now encountered a number of electrical gremlins that weren't present before.....

To cut a long story short, the vehicle has been parked for a few years, and has periodically been started/fettled with, but more recently i've been attempting to give her a new lease of life - and i'm getting there slowly. The interior developed a bit of mould from condensation etc, which may point to the issues, but I'd like a second opinion before I start stripping everything down if possible?

The issues I have now are:

  • Windows/mirrors/sunroof don't work - and the rear door switches don't work either
  • Fan blowers on full speed, and they wont turn down
  • Rear wiper doesn't work, nor does the wash
  • Interior light only works when the doors are opened, and not via the switch when doors are closed
  • SRS Airbag fault - been showing since I owned it 10 years ago and ive never been bothered by it, however its an MOT requirement now so I need to clear the fault. Tried the underseat connectors a few times but the fault still remains.

I have checked every fuse in the car, and all appears fine. Would any of the above faults point to a BECM that is on it's way perhaps?
 
Possibly corrosion on the BECM connectors, could also be the under bonnet fuse box, if you have diagnostics some of the things you have mentioned can be operated via diagnostics to narrow things down. What is the battery voltage?
 
Usually "in my experience" a BeCM on the brink causes things to happen when you don't want them to!
again In my experience, the rear window would work of its own accord and the interior light would flicker..

I'd check the carpet, the foam can get saturated with water and eek into the BeCM..

Also worth checking the underbonnet fuse box, give it a smell.
 
Thanks for your input gents.

Unfortunately i have no diagnostics to hand, and don't know anyone who does, however Ill measure the voltage at the battery to see if all is satisfactory there.

The fusebox appeared fine when I checked it - no signs of distortion or burning under any fuses/relays which is good. But i will check the carpets for any water too.
 
GavinDavis said:
Thanks for your input gents.

Unfortunately i have no diagnostics to hand, and don't know anyone who does, however Ill measure the voltage at the battery to see if all is satisfactory there.

The fusebox appeared fine when I checked it - no signs of distortion or burning under any fuses/relays which is good. But i will check the carpets for any water too.
Click to expand...

The fusebox can look ok, you have to get your snout in there and sniff it! ;)

A burning smell is the indicator!
 
my fusebox issue was where one of the 3 cables screwed down underneath, where the screw thred attached to the board, the solder had cracked, giving several intermittent issues.
for the SRS light, check both bulbs in the dash are good. also check the yellow connector under the dash for the steering wheel airbag, this got me last week
 
GavinDavis said:
Hi Guys,

Some of you may have seen a couple of my previous posts, whereby I recently changed the diesel injection pump on my 2000 DSE. All is now back together and running great mechanically, however I have now encountered a number of electrical gremlins that weren't present before.....

To cut a long story short, the vehicle has been parked for a few years, and has periodically been started/fettled with, but more recently i've been attempting to give her a new lease of life - and i'm getting there slowly. The interior developed a bit of mould from condensation etc, which may point to the issues, but I'd like a second opinion before I start stripping everything down if possible?

The issues I have now are:

  • Windows/mirrors/sunroof don't work - and the rear door switches don't work either
  • Fan blowers on full speed, and they wont turn down
  • Rear wiper doesn't work, nor does the wash
  • Interior light only works when the doors are opened, and not via the switch when doors are closed
  • SRS Airbag fault - been showing since I owned it 10 years ago and ive never been bothered by it, however its an MOT requirement now so I need to clear the fault. Tried the underseat connectors a few times but the fault still remains.

I have checked every fuse in the car, and all appears fine. Would any of the above faults point to a BECM that is on it's way perhaps?
Click to expand...

Windows mirror, sunroof etc - could be an issue with the 12V feed to the switchpack off the BECM, or it could be the switchpack itself - especially if there has been moisture in there. If you get 12V at the switchpack connector (should be there permanently and comes from F1 on the BECM), then chances are the switchpack has failed. I have seen them where they will inhibit the rear windows when they've completely failed, so the rear door switches don't work either. I repair switchpacks, so if this is the case I can either take a look at your one or supply a repaired/tested one on exchange.

Fan blower on full speed - this is usually down to a fault in the blower motor itself - there are a couple of speed transistors in there which can fail, and a common sign of them having failed is the blowers running at full all the time when the ignition is on. Is it just one of them which is running full all the time, or both?

Rear wash/wipe... this could be an output issue from the BECM - but could also be that it's not getting a proper input from the stalk. The wash is powered from the BECM, rather than the underbonnet fuse box (for the rear only) and the wiper is driven off a relay in the BECM - do you hear a click in the BECM when you try to operate the rear wiper? Silly question, but you don't have a TAILGATE OPEN message on the dash at all? If the vehicle thinks the tailgate is open (even if it isn't - could be a dodgy switch in the tailgate lock) then it won't operate the rear wash or wipe.

Interior lights - The switch is just an input trigger to the BECM - I've known for the tracks on the PCB where the connector plugs in (on the front interior light unit) to get corroded and cause strange issues. It's worth popping that out and checking it.

SRS fault.. on the later ones the fault will self clear once the problem is fixed - so if it isn't under seat connectors, then also worth trying the one for the steering wheel (do the steering wheel buttons/horn work? if so then the rotary coupler is probably fine). It could also be one of the warning lamps has burnt out - there are 2 of them, and even if one of then fails then it will throw a fault.

One other thing that could be worth checking is the bottom of the B pillars of the vehicle. There are seatbelt pretensioners on the later P38's aswell and thy connect to the SRS loom there - if one of them has a bad connection, then it could also cause your fault. Also worth checking the fuse in the underbonnet fuse box if you haven't already as the SRS unit gets it's power from F23 under there,

Whilst there *could* be a fault in the BECM - I don't think it is your only issue - and I wouldn't be surprised if there are a few different faults that are external to the BECM.

If you get to the point where you've traced everything and it does point to the BECM for some of the faults, then I'm happy to take a look at it - I've repaired a few random issues on them now. But I would be surprised if it was you main problem in this case!

Hope this helps,
Marty
 
What Marty said. If it has been sat and damp has got in then any switch on it could do with some contact cleaner and wriggling.

Whereabouts are you? Might be someone with diag nearby.
 
Datatek said:
The power cable connection to the fuse box can also corrode or come loose.
Click to expand...

I'll add that to my list of checks - can't get on it until the morning as I'm stuck at work :(

kermit_rr said:
my fusebox issue was where one of the 3 cables screwed down underneath, where the screw thred attached to the board, the solder had cracked, giving several intermittent issues.
for the SRS light, check both bulbs in the dash are good. also check the yellow connector under the dash for the steering wheel airbag, this got me last week
Click to expand...

Is the SRS light illuminated by two bulbs? Or is there a secondary fault light I should see? I have the red SRS and Airbag Fault on the digital readout.

Datatek said:
An SRS fault can be caused by low battery volts.
Click to expand...

I hoping to rule this one out as it's a recent battery that I bought - but I guess its always possible.

RangeRoller dt said:
Although it could be becm related I don’t think it sounds like that.
Mine was full of weird electrical gremlins after standing years, proper battery sorted the majority. Few others you mention are regular things
Click to expand...

I really hope it isn't the BECM! I'm waiting on a friend that might have a spare working switch pack for me to try.....fingers crossed!

martyuk said:
Windows mirror, sunroof etc - could be an issue with the 12V feed to the switchpack off the BECM, or it could be the switchpack itself - especially if there has been moisture in there. If you get 12V at the switchpack connector (should be there permanently and comes from F1 on the BECM), then chances are the switchpack has failed. I have seen them where they will inhibit the rear windows when they've completely failed, so the rear door switches don't work either. I repair switchpacks, so if this is the case I can either take a look at your one or supply a repaired/tested one on exchange.

Fan blower on full speed - this is usually down to a fault in the blower motor itself - there are a couple of speed transistors in there which can fail, and a common sign of them having failed is the blowers running at full all the time when the ignition is on. Is it just one of them which is running full all the time, or both?

Rear wash/wipe... this could be an output issue from the BECM - but could also be that it's not getting a proper input from the stalk. The wash is powered from the BECM, rather than the underbonnet fuse box (for the rear only) and the wiper is driven off a relay in the BECM - do you hear a click in the BECM when you try to operate the rear wiper? Silly question, but you don't have a TAILGATE OPEN message on the dash at all? If the vehicle thinks the tailgate is open (even if it isn't - could be a dodgy switch in the tailgate lock) then it won't operate the rear wash or wipe.

Interior lights - The switch is just an input trigger to the BECM - I've known for the tracks on the PCB where the connector plugs in (on the front interior light unit) to get corroded and cause strange issues. It's worth popping that out and checking it.

SRS fault.. on the later ones the fault will self clear once the problem is fixed - so if it isn't under seat connectors, then also worth trying the one for the steering wheel (do the steering wheel buttons/horn work? if so then the rotary coupler is probably fine). It could also be one of the warning lamps has burnt out - there are 2 of them, and even if one of then fails then it will throw a fault.

One other thing that could be worth checking is the bottom of the B pillars of the vehicle. There are seatbelt pretensioners on the later P38's aswell and thy connect to the SRS loom there - if one of them has a bad connection, then it could also cause your fault. Also worth checking the fuse in the underbonnet fuse box if you haven't already as the SRS unit gets it's power from F23 under there,

Whilst there *could* be a fault in the BECM - I don't think it is your only issue - and I wouldn't be surprised if there are a few different faults that are external to the BECM.

If you get to the point where you've traced everything and it does point to the BECM for some of the faults, then I'm happy to take a look at it - I've repaired a few random issues on them now. But I would be surprised if it was you main problem in this case!

Hope this helps,
Marty
Click to expand...

Wow!! Thanks Marty that was a pretty comprehensive read! Really appreciate the info and your offer to look at my BECM if it appears to be the issue - i'll do some checks over the weekend and i'll report back :)

Grrrrrr said:
What Marty said. If it has been sat and damp has got in then any switch on it could do with some contact cleaner and wriggling.

Whereabouts are you? Might be someone with diag nearby.
Click to expand...

Contact cleaner would certainly be a good option to be honest. I live in Redditch, Worcestershire :).
 
martyuk said:
Rear wash/wipe... this could be an output issue from the BECM - but could also be that it's not getting a proper input from the stalk. The wash is powered from the BECM, rather than the underbonnet fuse box (for the rear only) and the wiper is driven off a relay in the BECM - do you hear a click in the BECM when you try to operate the rear wiper? Silly question, but you don't have a TAILGATE OPEN message on the dash at all? If the vehicle thinks the tailgate is open (even if it isn't - could be a dodgy switch in the tailgate lock) then it won't operate the rear wash or wipe.
Click to expand...

Hi Marty,

I don't have a "tailgate open" warning - however I have recently rebuilt the spring and seal for the tailgate push button, and occasionally the lower tailgate appeared to stick and not open on the press of the button. After a few operations this is now working great, so I wonder if something might have been disturbed to cause this?
 
When illuminated they should blink at you. If it’s just on probably bulb. Not too hard get the bulbs out but leave it discharge thoroughly before you go pulling any connectors.

I did it other week, to no avail
Turns out I need a Nanocom. :(
02F46589-FE17-4C82-A766-E30EA76A9100.jpeg
 
Well I definitely don't see any blinking on mine - just a solid state red SRS, so hopefully it will be a simple bulb change to clear the fault.

Cheers for pointing out the two bulbs, are they available from any motor factors?

Good luck with yours.....I really could do with getting a diagnostic solution moving forwards too!
 
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