P38A Spurious Failure Warnings

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It's so shouting bad earth at me!!! Look everywhere. Get a few lengths of decent (2.5mm2 or above) cable and a handful of croc clips and take a few earth points from the battery neg to various parts of the engine/chassis/body and see what gives.
I'll bet a beer or 4 that it's an earth somewhere.
(Sorry, I accidentally posted this on someone else's thread too!!!)
 
Wazzajnr said:
It's so shouting bad earth at me!!! Look everywhere. Get a few lengths of decent (2.5mm2 or above) cable and a handful of croc clips and take a few earth points from the battery neg to various parts of the engine/chassis/body and see what gives.
I'll bet a beer or 4 that it's an earth somewhere.
(Sorry, I accidentally posted this on someone else's thread too!!!)
Click to expand...
Hi Wazzajnr,
I have some 6mm conductor cooker cable to play with and a spare set of soft-copper jump leads, but not sure where to apply it specifically. Pretty new to car electrics I'm afraid.
As long as I don't short anything out I guess it will be fine.
Surprising that it went from OK to "naff" in one big hit, but that is the nature of things I guess.
Thanks for the steer (you are not the first to suggest poor earthing somewhere either :D ) ....so maybe the clues are there ;-)
 
I've seen a few times now where the wiring from the ignition switch to the BECM is damaged/intermittent in the loom, so that randomly things keep dropping in/out all the time, with a variety of clicking of relays etc.

What actually turns off? do Radio/HEVAC drop out?

It's worth checking the continuity of the White/Pink wire, from the ignition switch, to the connector on the BECM.
It arrives on the BECM on pin 13 of the 16 pin white connector under the BECM fuse box (the bigger of the 2 white connectors - in the middle between the other white one and the yellow one). It can be accessed by removing the plastic trim - held in usually be a few 'fir tree' fasteners and a single screw.
 
martyuk said:
I've seen a few times now where the wiring from the ignition switch to the BECM is damaged/intermittent in the loom, so that randomly things keep dropping in/out all the time, with a variety of clicking of relays etc.

What actually turns off? do Radio/HEVAC drop out?

It's worth checking the continuity of the White/Pink wire, from the ignition switch, to the connector on the BECM.
It arrives on the BECM on pin 13 of the 16 pin white connector under the BECM fuse box (the bigger of the 2 white connectors - in the middle between the other white one and the yellow one). It can be accessed by removing the plastic trim - held in usually be a few 'fir tree' fasteners and a single screw.
Click to expand...
Hi Marty,
Everything seems to "Blink" if you will. The Satnav screen flashes, there is a "Beep" from the main console, the fans pause and instantly restart all gauges go to Zero (RPM for example) ; The engine (running) keeps running (momentum?) as the power instantly goes back on after this brief pause. Radio Is disabled (needs key code entering) so I will do that and see if it too drops its power.
Another "New" message on the console is "Keyfob Battery Low".
 
is there a main system relay?
had this on an Opel frontera. Most of the systems were dead apart from the engine running??
found two blown fuses and a duff heavy relay.!.!.!. ! Also a Volvo v50 system relay that would heat up and set the wipers going and the clocks off...left for 5 minutes and all was well..answer, heavier relay with it's cap left off...
 
DanClarke said:
Hi Wazzajnr,
I have some 6mm conductor cooker cable to play with and a spare set of soft-copper jump leads, but not sure where to apply it specifically. Pretty new to car electrics I'm afraid.
As long as I don't short anything out I guess it will be fine.
Surprising that it went from OK to "naff" in one big hit, but that is the nature of things I guess.
Thanks for the steer (you are not the first to suggest poor earthing somewhere either :D ) ....so maybe the clues are there ;-)
Click to expand...
Right, if it were me, I'd start by attaching a wire to the battery negative, then I'd clip the other end to a metal part of the engine. Try it, see if anything is different. If not then try battery negative to a non painted part of the chassis. No joy? Same again but to the bodywork. On the bodywork test, I'd try a number of different places as the body isn't one big lump welded or bolted together like chassis and engine.
 
Mark Piercy said:
i would start the car and put my ear to the under bonnet fuse box and listen for clicking that might match the glitching.
Click to expand...
That's where I started at the very beginning, RL-7 is going on & off in time with the reset's. The scorched nature of the relays suggested a change of the whole box.....which I did.
Something is telling it to restart the whole system....but what? Will try to check for a dodgy earth today while it isn't raining.
 
**UPDATE**
=========
Interesting.........
I just tried the "alternate earthing" approach between the -VE battery post and various parts of the body/engine. No difference.
But then........ While flitting between noisy engine bay and cyclically operating relays I though why not give it some revs?
Magically, as the revs go above idle and towards 2,000 the problem just goes away completely.
Now, I monitored the Alternator output volts to the battery and it was 14.3 at idle and 14.3 also under full load (main beams + Defrost program + heated seats + whatever else). So I believed the Alternator to be good.
But this revs-related wrinkle is obviously something to do with the problem. Any thoughts (other than always drive like a mad bastard in 1st gear that is)?
 
DanClarke said:
**UPDATE**
=========
Interesting.........
I just tried the "alternate earthing" approach between the -VE battery post and various parts of the body/engine. No difference.
But then........ While flitting between noisy engine bay and cyclically operating relays I though why not give it some revs?
Magically, as the revs go above idle and towards 2,000 the problem just goes away completely.
Now, I monitored the Alternator output volts to the battery and it was 14.3 at idle and 14.3 also under full load (main beams + Defrost program + heated seats + whatever else). So I believed the Alternator to be good.
But this revs-related wrinkle is obviously something to do with the problem. Any thoughts (other than always drive like a mad bastard in 1st gear that is)?
Click to expand...
Interesting, could it be that there is a bad connection from the battery to the fuse box? (+ve side I mean)
Not sure exact how it's wired, but I'd be using an alternative feed to the permanent live side of the fuse box and see what happens.
 
Hi Wazzajnr,
Thanks for the suggestion.
Well, the connection is a short 15" stranded cable that is sweated into the main battery +ve connector at the one end and arrives at the main fuse-box on a crimped ring connector.
I bypassed it with a jump lead and a screwdriver and it has made no difference. I am beginning to think Alternator (again!!).
The only thing electrical that varies with RPM is HT sparks and VOLTS/AMPS from the Alternator.
 
Measure the voltage drops between Alternator +ve and Battery +ve. Then do the same between battery +ve & fusebox +ve. Might show where something is wrong.

Would definitely be worthwhile getting a Nanocom onto it, to see what stored faults there are ? Then clear the faults, run the engine & read again.

Also wondering if one shorted diode in the alternator could do weird things ? Would this put AC ripple on top of the 14V DC output ?
 
DanClarke said:
Hi Wazzajnr,
Thanks for the suggestion.
Well, the connection is a short 15" stranded cable that is sweated into the main battery +ve connector at the one end and arrives at the main fuse-box on a crimped ring connector.
I bypassed it with a jump lead and a screwdriver and it has made no difference. I am beginning to think Alternator (again!!).
The only thing electrical that varies with RPM is HT sparks and VOLTS/AMPS from the Alternator.
Click to expand...

Crank & Cam sensors feeding engine ECU also vary with revs. Various other ECU's also use engine revs for different things.
 
pwood999 said:
Measure the voltage drops between Alternator +ve and Battery +ve. Then do the same between battery +ve & fusebox +ve. Might show where something is wrong.

Would definitely be worthwhile getting a Nanocom onto it, to see what stored faults there are ? Then clear the faults, run the engine & read again.

Also wondering if one shorted diode in the alternator could do weird things ? Would this put AC ripple on top of the 14V DC output ?
Click to expand...
For sure this could cause a problem that possibly a basic multimeter wouldn't show up.
It's a tough one without seeing it.
All I would say is that with many things wrong, it HAS to be an earth or a main feed causing it.
 
Having just entered therapy sessions for my recent BeCM induced ptsd (which are going well, incidentally), I think the culprit could well be the +ve feed to the very same or the unit itself.
Luckily there are wonderful people who can initially test and then repair if necessary. Vehicle wiring diagrams are available on the tinterweb with the attendant masses of info regarding earth locations etc etc.
From the symptoms it's almost like somethings tripping and resetting although why raising the rpm seems to sort things out is strange - it crossed my mind to suggest seeing what happens if you run the vehicle with jump leads connected to another healthy vehicle - two batteries in parallel would smooth out any ripples or abnormalities from the alternator.
Oh, here's nursey with the syringe again - must be that time already.........
 
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