Elunexpected results.ectrical glitch

[IanW]

Unexpected electrical glitch

On the way home this evening, I had an opportunity to test the kick-down operation, with unexpected results.

As the engine RPM went from approx. 1000 to 5000, the headlights went out, COMAND went off & the car hesitated. Within a second, everything is back to normal except for the new message in the instrument cluster - a red battery symbol and "Visit workshop".

The Memoscan gave the fault code P0563 "System voltage high", which I cleared & hasn't come back. I presume that the glitch was some form of overvoltage protection tripping and resetting.

I shall be measuring the battery voltage tomorrow - I'll build a little adapter to measure the voltage at the cigarette lighter, so I can check it while the engine is running under load.

Do I need to start saving for a new control module, or is it likely to be a software glitch?

The car is a 2005 CLK 500, with about 80K on the clock.

Ian.

 

[grober]

Sounds as if the car electrics experienced a little voltage spike- possibly induced by the kickdown action. May never happen again. If you want to experiment try duplicating the condition again- if its repeated then may point to problem with the kickdown switch or associate circuitry--- or something else entirely. Every time it happens I suppose you run the risk of more permanent damage occurring- how much to pursue it depends on how much you require the kickdown??? V the cost of protracted tracking down an intermittent fault. My advice would be "watchful waiting"--- if its anything serious its likely to increase in frequency/severity but if or until it does----?

 

[corned]

If it does happen again, I think you should test the output of the alternator, at the alternator output terminals and nowhere else.

Could be that the sudden spooling up of the engine revs (and therefore the alternator revs) temporarily defeated the voltage regulation circuitry in said alternator.

 

[Auto-mobile]

Personally if it was my car I would change the alternator, it has clearly spiked a high voltage, had this before on my Clio 172 when I bought it thE guy said it had a recon alternator, whenever it spiked (16.2v) on wot the headlamps went off and all the dash lights came on.

Not worth risking in my opinion

 

[BlackC55]

Dont change the alternator. Just the voltage regulator on the back of it. MB normally stock them as this has been an issue before.

 

[IanW]

Thank you all for your advice.

My preferred course of action *was* "watchful waiting", until I started the drive to work this morning. The gerry-rigged voltmeter clearly shows that the battery is not charging - in fact, even with all the unnecessary consumers off, the battery discharges at an alarming rate. From 11.5 volts after engine start, the 6 mile drive to the railway station took it down to 10.1 volts.

I shall be following BlackC55's advice & fitting a new regulator, and hopefully flagging this thread 'SOLVED' early next week. Fingers crossed.

Thanks,
Ian.

 

[Vlad]

I see that you are in Reading.....would be well worthwhile getting Star Motors to sort your alternator out.

Tel No 0118 9462750

 

[IanW]

All fixed!

It will surprise no one when I say that BlackC55's analysis was spot-on.
One new "regulator and cut-out" later and everything is hunky-dory. Overall, a very satisfying job, but if the weather hadn't been so good, it would have been straight round to Star Services.

A few observations on the procedure:
1. The charging system is a lot less sophisticated than I was expecting - a conventional 150 amp Bosch alternator, with the regulator mounted on the rear, and no over-run clutch.
2. I'm convinced that vehicle production starts with the alternator being placed on to the production line and the rest of the vehicle assembled round it. If the alternator needs to be replaced, it looks like an engine out job!
3. Given the experience, a set of right angled cross-head screwdrivers, 13mm and 15mm sockets, it should be simple to replace the regulator without unbolting the alternator. Once unbolted, the regulator is easily removed and comes out downwards. Since I was expecting to need to solder the connecions, I started by removing the accessory belt & unbolting the alternator. On the plus side, that did allow me to notice & replace the noisy idler pulley.
4. Depending on which storeman you talk to, there are either 2 or 3 possible regulator parts. You'll need to take the old part with you to make sure you get the correct one. In fact, for my 2005 model, the original (labelled F00M 145 333) has been replaced with part number MA003 154 52 06 - £30.90 + VAT from Greenoaks M-B.

Ian.