First post, please be gentle

My car has been exhibiting two odd electrical problems recently, the most regular and alarming of which is a sudden dimming of dipped beam within a few minutes of starting the car.

The loss of brightness occurs whether the engine is idling or not and lasts no more than about 2-3 seconds. As you might imagine it's very noticeable on unlit stretches of road at night, though the lamps quickly return to normal and strangely the problem won't recur that journey.

I've noticed this before in both the XJ8 and in plenty of other cars when punishing the electrics more than usual, such as with both heated seats, heated rear screen and so on, and most particularly when the A/C clicks in as well, but my car is doing this every trip now without any obvious trigger.

The other (almost certainly related) problem is that on a cold start two weeks back, I was using headlamps, heated rear, driver's heated seat and intermittent wipers when it dawned on me that that the wipers were operating in slow motion, on damp glass, at about one third normal speed. Having switched off the seat and the heated rear and tried the wipers again, they behaved normally. That isn't cast iron confirmation that the electrical drain was related, but it did seem that way at the time.

Is this something obvious like a duff battery, despite the battery not exhibiting any obvious signs of being duff - in that the car turns over fast and starts first time, every time? Could it be the A/C kicking in, or a problem with the A/C that exacerbates that? Something else? The car is used every day but has covered very few miles (circa 30K).

Thanks in advance for any and all wisdom received!

 

The car has power management software according to my Technical Notes of 2003, and will inhibit certain items if the generator/battery is unable to maintain a certain voltage in the electrical circuits.

I have to say your car seems to be suffering from "brown-out" so it could either be (1) duff battery, or (2) failing alternator, or (3) the power management is inhibited. This can be inhibited if one of the following cannot be measured: -

1. Engine speed
2. Road speed
3. ECT (not sure what this is, it's not in the glossary !)
4. Intake Air Temperature (from sensor)
5. System voltage at the ECM
6. Time since engine start

 

Fraser, thank you for taking the time to help.

I will try the most obvious - not to mention most cheapest - link in the chain first (ie battery) and then work from there.

I suspect that if it ends up being power management electronics then the local dealer is my only option

Much obliged

 

I'll be very interested in what you find.

I've a 2006 XJ6 with halogen headlights which I've owned for 4 years or so. For as long as I can remember my headlights dim for a couple of seconds, usually a couple of minutes after I've set off (obviously something I only really notice in winter). I also wondered if it was a load problem but could see no correlation with heated rear screen etc. I normally have A/C off, so I don't think its related to that. I did wonder whether it was related to the air suspension compressor running, but I've no real way to know.

I've not seen slow running wipers on my car, though they've always seemed to have a mind of their own (e.g. when set manually to intermittent wipe, they may still run continuously, or too quickly, or stop - seemingly dependent on the amount of rain).

Julian.