Dear All!

I just got my car (X-Type Exec., Aut., 2003, 3L V6) back from the MOT which found no problems.
But there is a problem...

I found this problem only for other types, I would appretiate any ideas, comments for the X-Type specificly.

It all started last July when the charge indicator lit up. I turned off all electronics and stopped as soon as possible. But the battery held the charge and the indicator did not come back after restarting the engine.
This has been happaning again and again since then. The charge indicator lits up, but dissapears when the car is restarted. It is more likely to happen on warm, sunny days.

In January my battery died on the road, but there was no charge indicator. It was a noname battery, it was replaced by a Varta 760 AGM Silver Dynamic battery.
A few weeks ago, I a parked the car after a long drive (100+km), and 6 days later the car did not start because this new battery died but run fine after recharging it.
When the light was on I measured 13.3-13.6 V charge on the battery with the engine running.
I decided to have my alternator replaced: I got a newly renovated original as a replacement.
Now I measure 14.6-14.7 V charge on the battery with the engine running when the light is on. Because the light keeps coming back, and dissapears when the ignition is swittshed off for a few seconds. I drove 150 km (cc 90miles) city+highway, with the light on the entire time, and no problem. The car drives perfectly.

What the hell is this?

Thank you!
Laci

 

Laci, depending on when you checked the voltage across the battery, the 14.5 VDC you saw may be a good voltage. Keep in mind that the X-Type has a "recovery" function in the charging system. So, for example, if you put a multimeter across your battery with it turned off, it will read 12.6 VDC. As you crank the engine, it will drop to about 11.0 VDC. As soon as the engine catches, you will watch it ramp up to 14.5 VDC and hang there for a few moments (it is all based on how the ECU sees the status of your battery. It will then ramp down to 13.7ish VDC. It does this to quickly restore the battery to 100% following the large draw that came from the battery to start the engine. Now, if you let the car idle for a minute or two and still have 14.5 VDC, then that is a problem. The system should have already ramped down.

Kinda like you can test the alternator by starting the car initially with nothing on. You should then be able to turn the dash fan on high, both seat heaters, rear defroster, and headlights and have the same voltage that you had with nothing on. If you find that the voltage drops to below 12.6 VDC, then you have an issue. Now, you add say wipers on fast, radio cranked up, and anything else you can turn on, then you might have a slight voltage issue at idle as the alternator cannot output its full 130 amps at idle (needs to get up to around 1500-2000 engine RPM).

Now, it is possible that the voltage sensing line is deteriorating and it is causing the ECU to see the wrong voltage. Kinda like you can have an issue with the line supplying the field voltage to the alternator. But then, all this could very easily be caused by bad battery terminals. The cables are well known for creating crazy problems like this due to their failures. A check you can do is start the car with the engine cold. As soon as the car gets started, turn on the dash fan to high, both seat heaters on high, rear defroster on, and headlights. Let the car idle for 5-10 minutes. Turn off all the electrical stuff and immediately cup your hand OVER!!!!!!! the battery terminals. Do they feel warmer/hotter than the surrounding metal? If yes, then you most likely have a bad battery cable. Notice I say OVER!!!! the battery terminal. Some people after doing this test have found their battery terminal hot enough to cook an egg on it. If this is your problem, do some looking here and there are tons of recommendations on what cables to get and what you need to look for.

 

Dear Chris,
Thank you so much! I did a little testing as you suggested:
after the night, before engine startup: 12.6V
After angine startup with all electronics switched off: 15.2V
Running idle for a few minutes (still everything off): 15.2V
Everything (seat heating, AC, radio, turned on, high beam etc) on: 13.4 and slowly decreasing to 12.6 (I assume it would had dropped more if I had let it run more). The battery terminals were not hot, and definitely not any warmer than the surrounding metal parts. I could easily touch them.
I turned off all electronics: 14.8V slowly dropping to 13.3V
Engine turned off: 13.0V
Restarting the engine: 15.0

Again, thank you so much for your ideas and help!

Laci

 

Laci, sounds like you have a wire that developing a high resistance and is getting warm as the car runs current through the wire. So, if you have a FLIR (thermal) camera, that will make finding the problem easier. But, that is not something that most people have just laying around. So, the next thing I would say then to do is to repeat the measurements using the large terminal on the starter as your point for the multimeter vice the battery terminals and see if you get the same indications/readings. After that, you will need to either access the alternator 3 wire plug or the ECM (ECM will probably be easier). You will want to locate an orange wire with a green stripe (terminal 3 on the alternator plug, pin 65 at the ECM). If you measure VDC, you should see a fairly low voltage (say 5-7 VDC) with the car at idle and the voltage down at 13.7 VDC. Then, as you turn on electrical stuff, that voltage will go up as more stuff is turned on. If you have 10+ VDC with nothing on in the car, then your ECM has an issue. If it is down around 5-7 VDC but you have 15+ VDC on the terminals, then your alternator has an issue. We can diagnose closer once we know a faulty component.

If you measure at the starter and see a different set of voltages, then odds are, you have either a bad wire between the alternator and starter or more likely the starter to the battery. It is possible that the terminal on the starter has some corrosion on it and that is causing your issues.

 

DearChris,
Thank you so much, this is super helpful. At least I am less stressed about the car suddenly braking down.
This is much over my capacities, I forward it to my mechanic, I believe he has thermal camera as well. He also has a guy who will go throught the car with an oscilloscope.
I will post any result here.
Laci

 

UPDATE
All wires look normal with a thermal camera and all connections as well. A mechanic (who writes software code for new Mercedes engines) took a very close look att he electronincs and found no fault. It seems certain that it has nothong to do with the alternator or the battery, more likely some misunderstaning inside the ECU.
So currently I have a data-recorder plugged into the OBD II port of the car monitoring everything and hopefully it will show us a hint.

 

I promised to return when this gets solved. It is hard to believe that it took almost 2 years. But DONE!
So to make the long story even longer, here is the final chapter:
Last summer we installed a recorder into the OBDII slot and kept it there for over 3 months. And it recorded nothing that could lead to the problem.
I measured the charging voltage and the battery voltage with and without the light on, warm and cold and a dozen other locations - always perfect.
For the autumn I kinda put it to rest a bit. The indicator kept turning on randomly and while it was extremely frustrating, it did no harm after all.
Late February on a sunny Saturday I drove cc 100km through mostly mountain serpentine - what a car, what a drive! I enjoyed every second. I stopped the car in the center of a beautiful town and spent a few hours with the family.
My GF walked to the car to pick me up from the restaurant, she started the engine, put the car in D - and the car did not move. Back N, return D - all fine. Maybe she did not fully pull the stick back? But when I sat in 5 mins later, the same. Same but worse. For a few minutes the car refused to move in D. No warning lights, no error messages or codes. Engine ran smoothly; the car moved in R but in not in D-2-3-4. The engine reacted to to the accelerator with a nice roar as it should - but the car did not move, acting as if it was in neutral. After a few desperate attempts it suddenly started moving and we drove home. It was not the joyride I had earlier. It acted as if the clutch was slipping or as if it randomly fallen back into N at lower speeds. But we got home and then went to my mechanics.
There were no error codes of any kind. There were no visible mechanical problems. The gearbox the preselector, the computer were all fine. But after an exhausting test there was a strange clue: when measuring the voltage at different components, he noticed that the values were mostly within the range but they were not consistent. On each connector the value always fluctuated a bit. The device showed continuous oscillation. With a brand-new battery and a brand-new alternator.
So he began clearing and polishing every single fuse and wire connector in the car. This is when he found that culprit: one of the main grounding points looked normal, but when he tried to remove the screw it turned out to be broken and it barely pushed the connector to the body. He fixed that, checked the other points, finished clearing the connectors. And the voltage values became a single consistent line.
He believes that this issue was behind everything. Ever since I drove 650 km (400+miles) and no warning light of any kind. Everything works perfectly. Better than ever.
So I hope, that this is solved, and may be it will be useful for someone.
Thank you for all the advice!

 

Thanks for the follow up post.