Dipped beam error - headlights working!?

[kdevitt]

Have had a dipped beam error on the check control for months now - not an issue as I was working on the car and just assumed a bulb was gone. I bought all new bulbs the other day and replaced them all - high / low beam and sidelights. All the bulbs are working fine now - but am still getting an error light on the check control.

Anyone have any idea where the issue could lie?

[ChrisHC]

When I had a similar problem with the brake lights it turned out to be a faulty earth connection, as so often with electrical problems. Try running a temporary wire from a good earth to both headlights in turn, and see if that solves the problem.

[paultv]

The active check control passes power to each lamp through a thick coil of wire - inside the coil is a reed switch - when current passes through a working bulb, the reed switch is activated - this kills the fail warning led - if the bulb blows, the reed relay drops out and the tell tale failure led comes on. If your lamp is working but the check stays on, it could be pin 3 active check unit to ground point G200 brown wire - or one of the reed switches is duff - there are 2 in series, one for Right and one for Left , so one failed reed will give a constant failure LED.

I would jump the earth and see if that fixes it - then pull the check unit and test the reeds.

Paul

[kdevitt]

Thanks guys - will do some more investigation!

[kdevitt]

Bit of a bump on this. Managed to eliminate the reed switches as being the issue - swapped in a known working relay and the issue is still there. When I bought the car, someone had hacked the check control unit in the headliner to remove some bulbs, so I'm figuring this is a long standing issue.

Would a duff K4 relay have any impact on this?

[Brianmoooore]

Missed this one first time around!
Can't see that a duff K4 would have any effect on this, other than the obvious that the dipped beams wouldn't be lit at full brightness.
Only 'bulb' in the display unit (UK version) is the on that illuminates the buttons. All the fault indicators are soldered in LEDs, and if the previous idiot has hacked his way in this far, there's a good chance that other damage has been done.
IF the headlamps are working as they should and are of equal brightness, then the easiest way forward would be to borrow a known working display unit and to try that.
Just remembered one bodge I came across once, where someone had attempted to fix one non working headlamp by linking it across to the working one, running two lamps of of one circuit and none of of the other. Check that fuses 13 and 14 each control only one light by pulling them out in turn.

[kdevitt]

Missed this one first time around!
Can't see that a duff K4 would have any effect on this, other than the obvious that the dipped beams wouldn't be lit at full brightness.
Only 'bulb' in the display unit (UK version) is the on that illuminates the buttons. All the fault indicators are soldered in LEDs, and if the previous idiot has hacked his way in this far, there's a good chance that other damage has been done.
IF the headlamps are working as they should and are of equal brightness, then the easiest way forward would be to borrow a known working display unit and to try that.
Just remembered one bodge I came across once, where someone had attempted to fix one non working headlamp by linking it across to the working one, running two lamps of of one circuit and none of of the other. Check that fuses 13 and 14 each control only one light by pulling them out in turn.

Haha - there were some interesting wiring in place to say the least when I got the car, and random speaker grilles screwed into the door cards.

The original check control computer did indeed have leds yanked out of it, my bad - forgot they weren't bulbs. The coolant level led was ripped out too, instead of just installing a new coolant level sensor! Have two check control displays - both showing the low beam error only.

Will check the fuse idea. Am I right in saying the low beam check control is built into the fuse box itself? There was some crappy hacking going on in and around the fuse box for tow bar electrics - getting concerned a new fuse box is the solution.

[kdevitt]

Fuses 13 and 14 working as they should too

[Brianmoooore]

Fuses 13 and 14 working as they should too

That's one possibility eliminated then!
You're quite correct that the dipped beam check relays are built into the fusebox. They're inside a small rectangular raised area that you an see on the deck of the fusebox, near fuses 13 an 14.
I've not experienced this particular fault with the check system (most faults are oil level or coolant level sensor related), but looking at the circuit diagram, I suspect that the yellow wire at pin 21 of the check panel is 12 volts + with the headlamps on (so that the system knows that the lights are on) and the signal on the yellow/black wire on pin 22 is the one from the check reed switches, which should be earthed when the lights are on and working, but open circuit to earth if one or both lights is not working, or they are switched off.
If this is so, the electronics would simply need to invert the reed switch signal, to give 12 volts + when things are OK, then use that signal plus the one from pin 21 to feed a simple NAND gate controlling the LED.

[kdevitt]

Thanks Brian - will do a bit more investigating. This might be a job which goes on the list for the lads at BMR when I eventually get the car over for some fettling!