VERY odd electrical fault '97 P38 4.6 HSE

paclx · Sep 28, 2014

Having just replaced the coolant expansion tank today (the tube at the bottom for the radiator bled pipe cracked and I lost 90% of my coolant) and bled the system, I then ran the engine to get up to temperature. All was fine, no leaks and steady temp gauge. Switched off to let it cool down.

30 minutes later I put the key in the ignition, and the message display came up with LH & RH front windows not set, fuse 8, 9, 10, 20 & 22 fail. I turned the key to position 1 to set the windows........windows wouldn't operate, and the audible alarm was very quiet. Turned the key back to position 0 the blowers came on. They stayed on even if I removed the key. The only way to get them to stop was by pressing unlock on the key fob!!!!! I tried this several times just to make sure it wasn't dreaming.

I'd recently had some odd electrical issues with blowers and cigar lighter failing momentarily, and fuse fault messages so I removed each maxi fuse 1 - 5 and then put them back. Key in, position 1 and everything was fine. Set the windows, the audible alarm was back to its annoying level, and off I went for a test drive. Did 8 km, no electrical gremlins, temp gauge was steady.

So does anyone have any ideas on what caused this round of electrical issues? I'm totally stumped!

ukadamwest · Sep 28, 2014

Battery ?

the P38's don't like weak batteries. If your battery is weak, or lots of little stop starts without being run enough to recharge it will drop the battery down starting it to run it takes a fair draw off the battery so unless it was run for 15 mins with no electrics going the charge remaining may be too weak. put the battery on charge and once charged see or if you have a voltmeter see what it reads across the terminals

paclx · Sep 28, 2014

I've had battery issues before, and have a good 3 stage charger to keep it topped up. I agree, the fuse faults (which were fine) could point to a low battery. BUT, it was the blower motors running when I removed the key that have got me very puzzled.

stopover · Sep 28, 2014

Perhaps you have dislodged a lead pack in the fusebox which is close to the water expansion bottle?? or got water in there?

Rick-the-Pick · Oct 1, 2014

This problem is caused by the under bonnet fuse box failing.

wil2813 · Oct 1, 2014

Rick-the-Pick said:
This problem is caused by the under bonnet fuse box failing.

+1 prob drownded

tomcat59alan · Oct 2, 2014

wil2813 said:
+1 prob drownded

+2, is it swimming in the fuse box ?

Littelwill · Oct 2, 2014

+3 seen the fuse box take a drink when topping up expansion tanks ;(

paclx · Oct 13, 2014

Stripped out the fuse box and dismantled yesterday. I found that the captive bolts for BeCM power are not that 'captive'. Obviously my 'tight' is more than the workshop manual 'tight'. Some evidence of coolant (or something) on the circuit board. I'll give the board a good clean, may add some conformal coating for good measure, and give the bolts plenty more solder and see how 'captive' it is this time.

forthbridge · Oct 13, 2014

Did you have a coolant leak under the header tank, if so it may be worth looking at the large electrical connector that sits underneath the header (big round plug)? I've had to check mine for corrosion before now and this coupled with what's been said about the fuse board is definitely a start. The coolant on the board is mentioned on here somewhere as a reason to have to replace the board, you may be able to search for the thread.

paclx · Oct 13, 2014

Yes, lost over 8l of coolant. Still the temp gauge didn't move off normal. Good point about the connector. I'll check it at the weekend. The board cleans well using alcohol and a Demel with a soft brush bit. I'll check the board with a Mega before I put it all back together.

Datatek · Oct 13, 2014

paclx said:
Yes, lost over 8l of coolant. Still the temp gauge didn't move off normal. Good point about the connector. I'll check it at the weekend. The board cleans well using alcohol and a Demel with a soft brush bit. I'll check the board with a Mega before I put it all back together.

Don't go near it with a Mega, you may blow the diodes.

paclx · Oct 14, 2014

Datatek said:
Don't go near it with a Mega, you may blow the diodes.

Can't see any diodes on the board.

Rick-the-Pick · Oct 14, 2014

They're between the two layers. Personally, when these fuse boxes take a hit of any fluid or burn up, the chances or a successful repair are very very slim.
But keep in mind, when these fuse boxes blow properly they can take every other ecu out with it.
They should be replaced every five years as it's a servicable item.

paclx · Oct 14, 2014

Rick-the-Pick said:
They're between the two layers. Personally, when these fuse boxes take a hit of any fluid or burn up, the chances or a successful repair are very very slim.
But keep in mind, when these fuse boxes blow properly they can take every other ecu out with it.
They should be replaced every five years as it's a servicable item.

Still cant see them. The board isn't bad, apart from the solder joints of two of the BeCM posts, which I will re-solder. I've been following this guide on repairing the fuse box Fuse Box Repairs It's very good

Datatek · Oct 14, 2014

paclx said:
Still cant see them. The board isn't bad, apart from the solder joints of two of the BeCM posts, which I will re-solder. I've been following this guide on repairing the fuse box Fuse Box Repairs It's very good

They can be repaired if the damage is not too bad, but still don't go near it with a Mega.

VERY odd electrical fault '97 P38 4.6 HSE

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