Canbus Gotcha

[GeoffL]

Not the motorhome this time, but I guess the same gotcha exists on motorhomes that use canbus ...

... Our car is booked in for MOT and service tomorrow. While giving it a quick 'once over', I noticed the bulb failure light come on and a quick check revealed that the front nearside sidelight was out. I replaced the bulb but no joy -- when I turned the sidelights on, although the offside light shone bright, the nearside light stayed out. So I checked the new bulb for continuity and found it OK. Next I checked the voltage at the bulb holder and got zero volts. I got the manual out and looked for fuses in case the sidelights were individually fused and noted that wasn't the case. So, as far as I could tell, both front sidelights were on the same circuit and I hence suspected a broken wire. (Cue much muttering and cursing!) I don't know why I did it, but in desperation I switched the ignition on to check whether the bulb failure light was still on. It went out after the 'power on self test' sequence and both sidelights were now shining brightly! What should have taken five or ten minutes had taken an hour and a half...

I guess that the moral of the story is that everything, even a lowly sidelight, is likely to be computer controlled on canbus vehicles and faults, no matter how mundane, might need to be reset after repairs are effected before the associated equipment will function properly.

 

[Ardachaidh]

It was much simpler when a man walked in front with a red lamp.

 

[SquirrellCook]

I have been warned a few times about changing all the bulbs, just for the sake of it. This is something I do on Murky every few years.
Apparently a new bulb might give a different reading to the original. So give a bulb fault

 

[Pudsey Bear]

I keep getting the bulb out icon too, but on checking they are all okay, then the icon goes out next time I fire it up, Canbus is pants.

 

[wildebus]

I keep getting the bulb out icon too, but on checking they are all okay, then the icon goes out next time I fire it up, Canbus is pants.

Interesting. in the last couple of months I get a phantom bulb warning on the dash as well but cannot find any that are not working when I check them all.

 

[Wrighpm]

Interesting. in the last couple of months I get a phantom bulb warning on the dash as well but cannot find any that are not working when I check them all.

Ha ha if it foxes you Wildebus then the rest of us a pretty FxxxxxD!

 

[SquirrellCook]

Just keep swapping bulbs until you cure it

 

[trevskoda]

I fitted new ones last autumn but was spring before I saw anything.

 

[GeoffL]

ISTR some pre-canbus cars I owned had bulb failure warning lights operated by comparing the current on each side and any difference triggered the system to light up the failure warning. So, for example, the warning would be triggered if you had different wattage bulbs or one side had some additional resistance. Also, you couldn't add trailer electrics by tapping into one of the rear light clusters because that too would create an imbalance. Perhaps the algorithm that detects bulb failure works the same way?

I keep getting the bulb out icon too, but on checking they are all okay, then the icon goes out next time I fire it up, Canbus is pants.

Interesting. in the last couple of months I get a phantom bulb warning on the dash as well but cannot find any that are not working when I check them all.