evenin' all;
SWMBO's Zafira developed a little 'feature' a couple of months back, finally got round to having a look today. Basically the TID is constantly showing 'brakelight'; although all 3 brake lights are in fact working. Poked around in the rear light clusters today, both brake light bulbs were rather black, although they've only been in a few months. Poking around with a DVM there is only 11.0V on the bulb when lit, which sounds a little low. I've replaced both bulbs and cleaned / bent the contacts in the cluster to make sure all is Ok, but still showing 'brake light' on the TID.
Any ideas anyone?
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With engine running this voltage should increase.I would be interested to know what the voltage drop is between the earth circuit on the bulb holder cluster and a good earth point on the body.How accurate is your dvm?hth
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The DVM is a Fluke 77 series2, acquired for a fiver when my employers shut the R&D dept. down:-((... ( big cloud, small silver lining ); so results should be reasonably accurate.
Good point; I'll try and check the cluster to chassis voltage tomorrow, plus I'll check the tail light voltage, to see if that's a bit low as well.
The Haynes manual for the Zafira has the new 'mickey mouse' style pictures of bits of the wiring, rather than the proper ISO circuit diagrams given in the Vectra B and Omega manuals, and misses the check control system off completely, so that's a fat lot of use.
Cheers doc.
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Fluke 77 sounds spot on to me! any more for a fiver!!?
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Fluke 77 sounds spot on to me! any more for a fiver!!?
Nah, we'll have to wait for the next department to be shut down ...... :-/
I got two of the 77s and a fair few hand tools for a tenner!
Unsurprisingly all the expensive test gear, 'scopes, spectrum analysers etc. went back to H.Q.
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there is only 11.0V on the bulb when lit
I suspect this'll be the cause. The check control works on resistance - if the voltage is too low then the resistance measured will be wrong and report back an error to the check control system. Even putting in the wrong wattage bulb (eg, a 6 watt side bulb instead of a 5 watt bulb) can upset the system.
Edited by Dynamic Dave on 20/12/2008 at 20:59
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mmm.. I haven't had chance to check for volts drop on the cluster earth point yet, but I removed fuse 38 and measured current flowing across the terminals there; 15mA with brake lights off (I assume this is the trickle current the check control uses to detect bulb failure), and 2.5A with the brake lights on, which sounds a bit low (ohms's law in action). I seem to have lost about 1.5V somehwere - all measurements with engine off.
I noticed that when I removed fuse 38 the TID (actually MID thinking about it ) changes from 'brakelight' to brakelight fuse'; I didn't realise it was that clever.
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I noticed that when I removed fuse 38 the TID (actually MID thinking about it) changes from 'brakelight' to brakelight fuse'; I didn't realise it was that clever.
I noticed that as well in the 2003 electronic Zafira handbook I downloaded some time ago from Vauxhalls website.
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Being an engineer of sorts I've never read the manual thoroughly ;-). Looking in the manual now the 'fuse' warning only occurs with the brake lights, not the headlights or tail lights. Not sure if my lovely green Vectra is the same, must see if I can find the manual for that.
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Don't know how sensitive the detection is, but (as you mentioned ohm's law) maybe the low voltage = low current which the system detects as a bulb fail?
JS
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>Don't know how sensitive the detection is,
The bulb fail circuit on my Jag is quite sensitive.
I had a brake light filament go a few months ago so replaced both lamps with some (Ring?) from a local motor factors. Within days it was telling me a brake light had failed again even though the lamps were OK.
Replaced both lamps with slightly more expensive Bosch units and no more problems.
Kevin...
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OK Folks;
Just had a few minutes out in the cold with the Fluke; a few more measurements ( all with engine off but ignition on unless stated otherwise) :-
Battery voltage : 12.55V
Voltage at live side of fuse 38 terminal, with fuse removed : 12.35V
Voltage between light cluster earth and chassis, with brake light on : 0.1V
brake light voltage at cluster connector with lights disconnected : 12.1V
brake light voltage at cluster connector with lights connected : 11.1V
Voltage at cluster connector with tail lights on : 12.05V
mmm.... maybe I'll splash out on a couple of Vauxhall bulbs, just in case they've 'fine tuned' the filament resistance, but this still doesn't add up properly from what I can see.
P.S. I've swapped fuse 38 with a new one in case it had increased resistance somehow.
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SC, have you tried measuring the voltage at the live connection of the cluster and chassis earth to see what readings you get?
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SC have you tried measuring the voltage at the live connection of the cluster and chassis earth to see what readings you get?
whoops, forgot that one; in theory it'll be 11.2V ( given the 0.1V drop between cluster earth and chassis ); but theory isn't stacking up too well so far on this one :-/
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The 1v drop doesn't look right to me.
I think there's a high resistance / poor connection either at a wiring multi-plug, or, at the switch itself.
It might be worth testing the voltage drop across the swich directly.
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Hi,
From what I can ascertain you have poor connections somewhere. If you have poor connections then this can cause lower voltage due to the resistance across the terminals. Black glazed bulbs are a dead givaway. Check the terminals at the bulb holder are in good condition and smear the bulb connections with petroleum jelly. Ensure your earth is a good earth with no restance across it. The least resistance there is, the better the connection and voltage loss will be kept to a minimum. Use quality Osram bulbs too.
hope this helps...
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>Voltage at live side of fuse 38 terminal, with fuse removed : 12.35V
What range is the DVM on?
0.2V drop with no current draw (fuse removed) looks odd to me, as does the half volt drop with the lamps removed. Once the DVM has settled I'd only expect 0V +/- 0.01V if there is nothing else in circuit. Is it a straight copper connection to the lights or electronically switched?
>brake light voltage at cluster connector with lights connected : 11.1V
>Voltage at cluster connector with tail lights on : 12.05V
Like NC and RtT I think you have a dodgy connection, probably between battery and fuse.
Kevin...
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I let the DMM autorange, so it's probably set to 20V FSD. If I can get one of the offspring to assist I'll try a direct terminal 38 to battery live terminal measurement this evening.
So far as I can tell from the rubbish wiring diagrams in the Haynes manual the brakes are mechanically switched.
I have no idea where the check control system is located, either physically or functionally, but I assume it works using a low value series resistance to monitor the current in the brake circuit, so there's another potential source of voltage drop.
Thanks for the feedback all.
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but I assume it works using a low value series resistance to monitor the current in the brake circuit
I don't know, but, it's also possible that using some turns of wire, the operating principle could be magnetic - possibly in conjunction with a Hall effect sensor.
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Just a quick update; the tail light on the opposite side blew today, so I replaced that stop & tail bulb ( which was also black inside), now the 'brake light' nag has gone away. I'm not at all convinced I've solved the root problem mind you.
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