mis3

I had a scary experience with my car today. My car is a 2004 CLK320 and the battery is 5 years old.

I started the car when I left the office. I had a malfunction "Visit Workshop" with a picture of a battery. The car drove OK so i went to the store. After the store, I could not start the car. After a few trials, the car finally started. I rushed home and there was a lot of traffic. The gas pedal was not too responsive and ABS and ESP malfunctions came on. There was no headlight, the dash went dim and I could not even wind down my windows. At one point, even with the gas pedal fully depressed, the car would not go faster than 15 kmh.

All of a sudden, everything came back to life. The headlights came back on and the gas pedal was responsive again. I drove for another 20km and arrived home safely. I restarted the car, it went OK and I still have the same "Visit Workshop" message.

I hooked up my battery charger and the display said my battery was less than 50%. I will charge the battery for the next few hours.

Now I have to figure out if the culprit is battery or the charging system. Any comments?

mis3

An update.

After charging for almost 3 hours, the battery was 90% full. Put the key in ignition and went to dyno mode. The voltage was 13.1v-13.1v. I started the car, the voltage went to 12.4v to 12.6v. The "Visit Workshop" malfunction came up again. I started the car twice and the results were consistent. I hooked up the battery charger and the battery is now below 50%.

Based on some readings on this forum, the voltage after started the car should be 14v. Does this mean that the alternator is toast?

Rudeney

It could be the alternator, but dead battery cell(s) can act like a giant resistor and pull down the voltage. Given the age of the battery, I would start there.

mis3

Using the a battery charger, the battery did charge. Doesn't this mean that the battery is okay?

One thing strange was when everything went south (non-responsive gas legal, no power windows, no headlights, no dash, etc), it recovered all of a sudden.

After the battery charger, after starting to car, it would go from 13.2v to 12.4-12.6v.I let it run for 2-3 minutes, the voltage would not go beyond 12.6v. Since the correct voltage should be over 14v, this shows that it is a bad alternator, right?

Another possible culprit is the voltage regulator.

iyeoh

Sounds like your battery has a bad cell that is acting up sometimes. When it misbehaves, voltage drops too much and everything goes haywire. When it works, all is well for a bit, until the cell acts up again.

It has happenned to me before on a different MB. Just because the battery charges up does not mean that the battery is good. "Visit Workshop" is pretty much a sign that the battery is toast.

It doesn't sound to me that it's the alternator, but that's a guess. I would replace the battery first. Much easier and costs less.

mis3

Just got it fixed. The culprit was the alternator.

I went to my indie this morning and he tested and determined that the alternator was not charging the battery. He ordered a reconditioned alternator (Bosch AL0787X) and surprisingly, the parts arrived in about 15 minutes. He replaced the alternator and the whole job took maybe 1 hr 15 minutes. He charged me $524CAN for the job (parts + labour + tax). The alternator carries a 2-year warranty.

I went to a few places afterward. I monitored the battery voltage and it was 14.1-14.4v consistently while driving. It would drop 0.6v when rear defrost was turned on. It would drop another 0.6v when I turned on the ventilation fan full blast. The new alternator seems to be working fine. Just in case, I will carry my jumper cable in my trunk in the next few days.

I know that Autohausaz sells the same reconditioned alternator for $190US. I also found a Canadian online store who sells it for $240CAN. I could not wait because this is my daily commute. Also, it's more work because I would have to return the old part.

I have decided not to charge the battery overnight as suggested by the indie. If my car will start tomorrow, my alternator/battery are okay.