CDI parasitic draw woes - PeachParts Mercedes-Benz Forum

spark3542 · #1 01-29-2023, 03:46 PM

Here’s the current update (no pun intended)…

Cant find a fused circuit that is drawing…pulled all fuses one at a time

Assume possibly that voltage regulator is drawing when vehicle is off (battery will be too dead within about 18 hours of shutting off vehicle).

Installed new regulator (took 2 tries to get the right regulator…the most common one has a connector that comes straight off the back, but that interferes with charge air pipe, so special regulator with connector off to the side is required for the diesels).

Now immediately after start I get red battery screen of death and all “convenience” functions are disabled. I confirmed both from obd2 and voltmeter that alternator is charging. I even swapped batteries

Anyone have any insight as to why regulator change would give this screen? Again alternator IS charging, and battery IS good, but all convenience function remain disabled as long as the engine is running

dieselbenz1 · #2 01-29-2023, 04:21 PM

Strange one would think its the battery monitor/switch in the trunk but that doesn't really make any sense. Rollguy had issues with his regulator at least in the thread it gives the correct part number.
http://www.peachparts.com/shopforum/diesel-discussion/418574-05-cdi-communication-fault-n14-2-glow-output-stage-2538-4-jay-bob.html

Mxfrank · #3 01-29-2023, 06:20 PM

The alternator itself can cause parasitic draw. The reason would be a weak diode. The best way to diagnose would be to view the waveform on an oscilloscope. You can do a quick and dirty ripple voltage check with a multimeter by setting it to measure AC voltage. Measure at the positive battery post with then engine revved to about 1500 and the headlights on. If you have more than 100mv of AC ripple, the alternator needs to be checked further.

The VR itself cannot cause this problem, unless there's a bad diode in the D+ trio. If this is the case, you may not see a problem with AC ripple.

TimFreeh · #4 01-29-2023, 09:28 PM

Quote:

Originally Posted by spark3542

....Now immediately after start I get red battery screen of death and all “convenience” functions are disabled. I confirmed both from obd2 and voltmeter that alternator is charging. I even swapped batteries

Anyone have any insight as to why regulator change would give this screen? Again alternator IS charging, and battery IS good, but all convenience function remain disabled as long as the engine is running

The red screen isn't necessarily telling you the alternator isn't charging.

This message is triggered by the battery control module doing an evaluation and finding that in its opinion there isn't sufficient charge in the battery and it will be disabling the conveince functions until such time as a sufficient charge in the battery exists. I've had this message before when I've left my car in a garage for extended periods of time without a battery maintainer in operation. I've also had it when I had a marginal battery.

If your alternator is charging this message should disappear within 5-10 minutes of driving and you'll get a message on the cluster that the convince functions are once again operational.

You could test your theory that the alternator is causing the parasitic draw by disconnecting the plug and seeing if the draw goes away.

Zulfiqar · #5 01-30-2023, 05:25 PM

Quote:

Originally Posted by spark3542

Here’s the current update (no pun intended)…

Cant find a fused circuit that is drawing…pulled all fuses one at a time

Installed new regulator (took 2 tries to get the right regulator…the most common one has a connector that comes straight off the back, but that interferes with charge air pipe, so special regulator with connector off to the side is required for the diesels).

Now immediately after start I get red battery screen of death and all “convenience” functions are disabled. I confirmed both from obd2 and voltmeter that alternator is charging. I even swapped batteries

Anyone have any insight as to why regulator change would give this screen? Again alternator IS charging, and battery IS good, but all convenience function remain disabled as long as the engine is running

Firstly - you cannot remove fuses to find a battery draw on these cars as removal and install of a fuse can wake up a module and that module wont go to sleep/dark mode until its cyclic sequence - e.g. car locked etc.

Secondly - you have the wrong regulator on the alternator, the linbus is not able to communicate with and hence is showing that error, the good thing is that mercedes have designed it such that it will bootstrap itself and start charging the battery to full juice after a period of 10 seconds of no communication from the alternator regulator.

to find the draw, open the doors, trunk, hood etc and then lock all the latches with a screwdriver along with taping all the push buttons shut to fool the car that all doors are closed - then lock the car and leave it alone for about 10 minutes.

now one by one use your multimeter on 20DCV and check the voltage drop across all fuses and write them down.

find the bad circuit with this
https://www.underhoodservice.com/tech-tip-volkswagen-diagnosis-for-excessive-static-current-draw/

spark3542 · #6 01-31-2023, 12:17 PM

Quote:

Originally Posted by Zulfiqar

Firstly - you cannot remove fuses to find a battery draw on these cars as removal and install of a fuse can wake up a module and that module wont go to sleep/dark mode until its cyclic sequence - e.g. car locked etc.

Secondly - you have the wrong regulator on the alternator, the linbus is not able to communicate with and hence is showing that error, the good thing is that mercedes have designed it such that it will bootstrap itself and start charging the battery to full juice after a period of 10 seconds of no communication from the alternator regulator.

to find the draw, open the doors, trunk, hood etc and then lock all the latches with a screwdriver along with taping all the push buttons shut to fool the car that all doors are closed - then lock the car and leave it alone for about 10 minutes.

now one by one use your multimeter on 20DCV and check the voltage drop across all fuses and write them down.

find the bad circuit with this
https://www.underhoodservice.com/tech-tip-volkswagen-diagnosis-for-excessive-static-current-draw/

It's definitely the wrong regulator The car cranked and lit off fine (strong battery), and dash immediately went to this screen. You can see from my scangauge at bottom of pic that alternator is charging. It won't let me dismiss this screen. It was mildly unsettling driving 25 miles with this screen up the whole time.

On a bright note, Later (with the car off) I left the ammeter on the negative cable until the car went to sleep, and got a sleep reading of only about 10mA, which is acceptable. Perhaps root cause was bad regulator.

I have a junkyard alternator (from 05 CDI) on its way, while I procure the correct regulator (P/N Bosch F00M 144 132). Ultimately I hope to have a good spare alternator for any of the other 3 CDI's

Zulfiqar · #7 01-31-2023, 05:38 PM

You will need to verify with the dealership of what kind of alternator you need, even on CDI models you can have 2 different types depending on what was originally specced for your certain car.

ROLLGUY · #8 02-01-2023, 01:30 PM

My '05 CDI parasitic draw is back. After trying different ways to diagnose the draw, I came to the conclusion (so I thought) that the voltage regulator was bad: http://www.peachparts.com/shopforum/diesel-discussion/418574-05-cdi-communication-fault-n14-2-glow-output-stage-2538-4-jay-bob.html
A couple weeks ago, the turbo lost all it's bearings, and was blowing out a "James Bond" style smoke screen. I ordered a turbo cartridge, and will install it today (arrived yesterday). I went to move the car (was sitting for a week), and the battery was COMPLETELY DEAD! I took it out and charged it overnight. In the morning it only had 6 volts. Needless to say, the parasitic draw has NOT been fixed. I have an amp clamp meter on order, and hope it will help with diagnosing the problem. The last thing I tried was to open the trunk and doors, tripping the latches, and waiting a while. I then used the milliamp method to check all the fuses, using the chart found online (each amp rating fuse has a specific value listed on the chart). I found nothing wrong, and all the circuits were within the limits. That is when I assumed the only thing left was the voltage regulator. Now I am not sure what to do. I really don't want to ruin another $150 AGM battery.

dieselbenz1 · #9 02-01-2023, 01:53 PM

Not certain if you have a blue tooth but that gave me headaches a while ago.

http://www.peachparts.com/shopforum/diesel-discussion/402018-05-cdi-parasitic-drain.html

ROLLGUY · #10 02-01-2023, 03:40 PM

Quote:

Originally Posted by dieselbenz1

Not certain if you have a blue tooth but that gave me headaches a while ago.

http://www.peachparts.com/shopforum/diesel-discussion/402018-05-cdi-parasitic-drain.html

No bluetooth.

ROLLGUY · #11 02-01-2023, 03:44 PM

Can I use my SDS for finding a parasitic draw?

dieselbenz1 · #12 02-01-2023, 04:10 PM

Sort of there is an amperage reading in the battery module you can read. I did that but was drawing current from my foxwell in addition to the load and inspecting any module wakes it up so it gets real confusing. Problem is the offending module might wake up anytime I found that out when I just used a light bulb instead of a current meter. After about an hour I noticed the bulb get real bright when the module woke up. I'm still learning how to deal with these highly integrated systems.

spark3542 · #13 03-06-2023, 03:16 PM

Just to update the group…i still have parasitic draw after changing out the alternator. I haven’t had time to root cause any further in the last few weeks, so i put a charger on whenever i might go over 18 hours between starts…pretty annoying.

Zulfiqar · #14 03-06-2023, 08:13 PM

check the module under the driver seat - infact just disconnect it and see what it does to your case.

ROLLGUY · #15 03-07-2023, 09:40 AM

Quote:

Originally Posted by spark3542

Just to update the group…i still have parasitic draw after changing out the alternator. I haven’t had time to root cause any further in the last few weeks, so i put a charger on whenever i might go over 18 hours between starts…pretty annoying.

I changed the alternator as well, and that did not solve the problem in my niece's car. I found out that the CD player was in a tizzy, and was the source of the draw. I was told that the radio has not worked since about the time the battery started going dead. I removed both fuses (CD & radio), and the draw went away. The car sat for almost two weeks, and still was able to start. Once I put the fuses back in, opened the CD changer door, the radio came back and everything works! I used an amp clamp to monitor the modules gradually sleeping, and confirmed that the draw was gone.