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Welcome to what could be a very long diagnosis. Intermittent faults are usually the hardest to find. Don't be fooled into changing anything at the start unless there is unequivocal proof that it's the fix.
There are too many stories here of people who've unloaded the parts canon on their cars at great cost, and yet they still have the problem, or it turned out to be something simple they overlooked at the start.and theyve spent a heap of cash on parts they didn't need.
Time, research and a scan tool will help as well as a good independent MB mechanic.
I'd suggest like CaliBenz that you most likely have an ECU or harness/wiring fault. Preparation prior to diagnosis is the key. Start with checking battery (incl terminals) and alternator to make sure everything has adequate voltage. 11.7v minimum engine off and 13.7v engine running. Then the ground wires and connections to make sure there's no corrosion and they have a good contact base.
After that, you can then start on more specific areas depending upon where your research and advice sends you. Its essentially a process of elimination. Best ot luck.
I just checked the vehicle data and embedded photos of the results for the battery with engine off and engine on, plus my engine type. (Engine on reading was made with climate control on, radio on and headlights on -- I didn't think at the time to turn them all off.) Running doesn't match the 13.66 my Launch scanner said (with no climate control, radio or headlights), but I guess that fluctuates...?
I found out my drivers mirror is heated when I was fiddling around with my Mercedes scanner, came across an option to test it, turn it on and off using the scanner. I think it works automatically when the heat is turned on, or maybe the defrost. I was thinking maybe the code didnt come back because the heated mirror function hasnt been used since clearing the codes, or it was a random code and fixed itself.
I think the fuel filler flap actuator is mounted to the back of the filler door assembly. Its what lock/unlock the door from being opened. I know my fuel door wont open unless the car is unlocked. looking at the parts diagram it shows a harness at the filler door (900). And part 440 is the emergency pull located in the trunk if theres an electrical problem so you can get the door opened.
Try your door, see if its always opened.
photo os a used filler door on eBay, can see the electrical connection.
I tried the fuel filler door when the car is locked and the little door is locked unless I unlock the car.
I just checked the vehicle data and embedded photos of the results for the battery with engine off and engine on, plus my engine type. (Engine on reading was made with climate control on, radio on and headlights on -- I didn't think at the time to turn them all off.) Running doesn't match the 13.66 my Launch scanner said (with no climate control, radio or headlights), but I guess that fluctuates...?
These two pics show :
Low battery voltage w/ engine OFF
High current with engine ON
So the direct conclusion is battery is in discharged state. That much is for sure!
Countless reasons why that can be including dangerous "drain while driving" of concern here.
You noticed the live voltage is very dynamic. It is controlled by ECU... sometimes part of that logic fails due to poor GND reference.
Extended Test Drive:
-- Drive with this display selected and watch if BAT voltage ever deeps below 12.3V or while driving longer than 45mn.
-- STAY OUT OF FAST LANE!!
> Catch-22 Question :
is it the ECU crash that causes low voltage ?
or is it low voltage that crashes the ECU ?
I vote No1+2, both!
Poor chassis GND skew the voltage reference that gets increasingly lower until enough conditions soft-crash the ECU into scary "limp-mode".
Just clean stupid painted GND ✌️
ECU uses multiple separate circuits (power vs. signal) with distinct voltage references. 👏
Last edited by CaliBenzDriver; 02-20-2024 at 03:39 PM.
Guess im confused. I don't see that 11.7v as bad. Sure the engine is not running but the car is still turned on and all the electronics are running, fuel pump, etc.
When i was fiddling around with my 2 battery testers my battery showed 11-12v engine not running. As soon as the engine started it ramped up to over 14v.
So the direct conclusion is battery is in discharged state. That much is for sure!
Countless reasons why that can be including dangerous "drain while driving" of concern here.
You noticed the live voltage is very dynamic. It is controlled by ECU... sometimes part of that logic fails due to poor GND reference.
Extended Test Drive:
-- Drive with this display selected and watch if BAT voltage ever deeps below 12.3V or while driving longer than 45mn.
-- STAY OUT OF FAST LANE!!
> Catch-22 Question :
is it the ECU crash that causes low voltage ?
or is it low voltage that crashes the ECU ?
I vote No1+2, both!
Poor chassis GND skew the voltage reference that gets increasingly lower until enough conditions soft-crash the ECU into scary "limp-mode".
Just clean stupid painted GND ✌️
ECU uses multiple separate circuits (power vs. signal) with distinct voltage references. 👏
Guess im confused. I don't see that 11.7v as bad. Sure the engine is not running but the car is still turned on and all the electronics are running, fuel pump, etc.
When i was fiddling around with my 2 battery testers my battery showed 11-12v engine not running. As soon as the engine started it ramped up to over 14v.
It's enough voltage so things appear to work, but just not very well. Modules hate even a small drop in voltage. 11.7v is your battery dying unfortunately. 14v is the alternator topping up the system. If you put a load tester on the battery, rather than just read the voltage, it will show its inability to withstand a large draw on its capacity. I used to want to believe that anything over 11v was OK "She just needs a charge" but no.
I went to double check and see my battery did not appear to drop below 12v, so I may be wrong with my comment above.
I wrote a threat documenting what I thought was a battery issue at the time, now i think it was just in my head. I ended up buying two different battery testers to see what was going on. I never bothered looking at the battery voltage thru the dash board. The testers worked by connecting directly to the battery, key not in ignition. Unless I was driving around. heres some screen shots of the readings.
Guess im confused. I don't see that 11.7v as bad. Sure the engine is not running but the car is still turned on and all the electronics are running, fuel pump, etc.
When i was fiddling around with my 2 battery testers my battery showed 11-12v engine not running. As soon as the engine started it ramped up to over 14v.
Yes, this can be confusing... we'll keep this simple.
Keep glancing at IC Display "Batt volt/amp" to see voltage getting too low while driving.
If below 12.3V park the car safely then restart it while stopped.
It's enough voltage so things appear to work, but just not very well. Modules hate even a small drop in voltage. 11.7v is your battery dying unfortunately. 14v is the alternator topping up the system. If you put a load tester on the battery, rather than just read the voltage, it will show its inability to withstand a large draw on its capacity. I used to want to believe that anything over 11v was OK "She just needs a charge" but no.
Alleged 72 month battery is 54 months old and Interstate only makes you whole if it fails at 30 months or less, so I guess I can ask the shop that installed it if I get a discount on a replacement since we are still 18 months short. (Then again there was a period during shutdown where I hardly drove, so maybe that screwed things up...?) But I'm curious if people think that Interstate is a good battery brand for a Benz? I posted prior that my Mercedes branded batteries each died after less than 36 months.
Last edited by Aging C300; 02-20-2024 at 04:06 PM.
Youtube "Carbon Pile Tester" and you'll see the load testers that are the most definitive way to test a battery. Battery testers are good in that they show voltage, CCA etc, but they don't put enough of a draw on the battery to really test it. Some of the carbon pile testers can put up to a 500A load on the battery which the rest can't. I'll admit I struggled with the concept that 11.7v wasn't enough. But that was me coming from old school muscle cars where as long as it started, who cared?
Yes, this can be confusing... we'll keep this simple.
Keep glancing at IC Display "Batt volt/amp" to see voltage getting too low while driving.
If below 12.3V park the car safely then restart it while stopped.
My commute home in torrential rain on a So Cal freeway (the 405, probably the worst in the universe) will be interesting as I glance at the data! Update to follow.
I went to double check and see my battery did not appear to drop below 12v, so I may be wrong with my comment above.
I wrote a threat documenting what I thought was a battery issue at the time, now i think it was just in my head. I ended up buying two different battery testers to see what was going on. I never bothered looking at the battery voltage thru the dash board. The testers worked by connecting directly to the battery, key not in ignition.
Unless I was driving around. heres some screen shots of the readings.
Ok great, lets not confuse everything:
The battery is tested as GOOD
The tester says RECHARGE.
That means battery is DISCHARGED like I was saying above by looking at high charge current.
The battery is *NOT* causing this car to limp-mode.
Then something else is... ECU GND REF.
The reason we look at the ECU screwing up the voltage control is because active regulation acts a marker of ECU software crashing: thread topic.
There's no direct fault code I know of to flag that limp-mode on the freeway. It's hush-hush.
Last edited by CaliBenzDriver; 02-20-2024 at 04:18 PM.
Alleged 72 month battery is 54 months old and Interstate only makes you whole if it fails at 30 months or less, so I guess I can ask the shop that installed it if I get a discount on a replacement since we are still 18 months short. (Then again there was a period during shutdown where I hardly drove, so maybe that screwed things up...?) But I'm curious if people think that Interstate is a good battery brand for a Benz? I posted prior that my Mercedes branded batteries each died after less than 36 months.
Where the replacements AGM or lead acid? There's a difference in opinion as to whether a lead acid battery is good enough for these cars. My factory AGM battery (Varta from memory) lasted 10 years and that is common place. Some go longer. I replaced it with a lead acid battery. 4+ years in, so far so good. Im surprised that your MB branded ones have failed so quickly.
Batteries hate being drained. That's what kills them. Short trips after that don't help as they've enough current to operate, but never get the chance to fully charge, so their life is drastically shortened. I stick mine onto charge for 6 or so hours every 6 months.
But if you've been through so many AGM ones, and you're condident that you haven't let them drain, it's possible they're draining via a parasitic draw that you're not aware of. That is, they're draining enough to damage the battery, but still have enough to start so you don't notice it.
Where the replacements AGM or lead acid? There's a difference in opinion as to whether a lead acid battery is good enough for these cars. My factory AGM battery (Varta from memory) lasted 10 years and that is common place. Some go longer. I replaced it with a lead acid battery. 4+ years in, so far so good. Im surprised that your MB branded ones have failed so quickly.
Batteries hate being drained. That's what kills them. Short trips after that don't help as they've enough current to operate, but never get the chance to fully charge, so their life is drastically shortened. I stick mine onto charge for 6 or so hours every 6 months.
But if you've been through so many AGM ones, and you're condident that you haven't let them drain, it's possible they're draining via a parasitic draw that you're not aware of. That is, they're draining enough to damage the battery, but still have enough to start so you don't notice it.
The AGM are a great upgrade to cheap liquid lead-acid.
Mine is original and going on its 11th year. It survived the 90Amp deep drain by ALT controlled by the Bosch ECU wired carefully in Mercedes-Benz with painted GND posts.
Last edited by CaliBenzDriver; 02-20-2024 at 04:33 PM.
The battery in my car when I bought it was a Mercedes battery and that lasted 7yrs according to the manufacture date stamped on it. I replaced it with the same H7 Mercedes battery from the dealer, it was $201 + tax with $30 refundable core charge.
I dont drive my W204 that much which is why I bought a charger, hook it up once a week.
I was just posting the tester screen shots to show I was wrong in thinking my battery went below 12v, it hadn't. My memory isn't that good which is why I take photos of everything. Those are cheap $15 battery testers and not very accurate. The tester with the app doesn't even let you switch to agm battery or input the CCA's, the Konnwei does at least so I think that may be slightly more accurate.
Where the replacements AGM or lead acid? There's a difference in opinion as to whether a lead acid battery is good enough for these cars. My factory AGM battery (Varta from memory) lasted 10 years and that is common place. Some go longer. I replaced it with a lead acid battery. 4+ years in, so far so good. Im surprised that your MB branded ones have failed so quickly.
Batteries hate being drained. That's what kills them. Short trips after that don't help as they've enough current to operate, but never get the chance to fully charge, so their life is drastically shortened. I stick mine onto charge for 6 or so hours every 6 months.
But if you've been through so many AGM ones, and you're condident that you haven't let them drain, it's possible they're draining via a parasitic draw that you're not aware of. That is, they're draining enough to damage the battery, but still have enough to start so you don't notice it.
I looked up my current battery on the Interstate site -- it is lead acid with a 6-year performance warranty. I have to dig deeper to see what battery the dealer used.
-- Batteries are on the receiving end of poor voltage control. Batteries arenot the root-cause of "highway stalls".
-- When the driving chassis voltage deeps down too low then everything starts disfunctioning dangerously.
-- For a while strong batteries can help make up for missing power until it is exhausted. Then the chassis is defenseless against glitchings that tank COMS.
Good Voltage + LOW Amperage: nice ECU job: 100% charged!
I get three dynamic voltages :
14.9V during decelerations
14.4V during normal cruising
13.7V during accelerations
(12.6V during float... M.I.A!)
All along the current is decreasing as battery is absorbing charge all the way to 100%.
Alternator supplies 100% of all running demand, battery does nothing while engine is running, except smooth out voltage ripples.
Last edited by CaliBenzDriver; 02-20-2024 at 08:10 PM.
2015 SL400 (M276 Turbo), 2014 C350 Sport (M276 NA), 2004 SL500 (M113), 2004 Audi TT225 (BEA)
Did you buy your Interstate battery from an Interstate store or from Costco? I've heard Interstate batteries from any place other than an Interstate store (to include independent shops) are not the same quality.
Did you buy your Interstate battery from an Interstate store or from Costco? I've heard Interstate batteries from any place other than an Interstate store (to include independent shops) are not the same quality.
So the direct conclusion is battery is in discharged state. That much is for sure!
Countless reasons why that can be including dangerous "drain while driving" of concern here.
You noticed the live voltage is very dynamic. It is controlled by ECU... sometimes part of that logic fails due to poor GND reference.
Extended Test Drive:
-- Drive with this display selected and watch if BAT voltage ever deeps below 12.3V or while driving longer than 45mn.
-- STAY OUT OF FAST LANE!!
> Catch-22 Question :
is it the ECU crash that causes low voltage ?
or is it low voltage that crashes the ECU ?
I vote No1+2, both!
Poor chassis GND skew the voltage reference that gets increasingly lower until enough conditions soft-crash the ECU into scary "limp-mode".
Just clean stupid painted GND ✌️
ECU uses multiple separate circuits (power vs. signal) with distinct voltage references. 👏
Glancing periodically at voltage data while on the freeway during my commute, the range was 13.6-14.5, but most often 14.0-14.1. Once off the freeway it fluctuated a lot more — as low at 12.9 for a millisecond and as high as 14.8 for a millisecond, but still mostly 14.0-14.1. After about ten minutes with the engine off it reads 11.8.
Glancing periodically at voltage data while on the freeway during my commute, the range was 13.6-14.5, but most often 14.0-14.1. Once off the freeway it fluctuated a lot more — as low at 12.9 for a millisecond and as high as 14.8 for a millisecond, but still mostly 14.0-14.1. After about ten minutes with the engine off it reads 11.8.
That sounds okay. Voltage is dynamically managed by the ECU based on what the engine is doing.
What were the Amp numbers during that time... from 10A down to near zero?
Try not to drain the battery listening to the radio engine OFF. It is doable but not best-practice for battery sake. ECO emulates drain cycles real well.
Last edited by CaliBenzDriver; 02-21-2024 at 04:04 AM.
That sounds okay. Voltage is dynamically managed by the ECU based on what the engine is doing.
What were the Amp numbers during that time... from 10A down to near zero?
Try not to drain the battery listening to the radio engine OFF. It is doable but not best-practice for battery sake. ECO emulates drain cycles real well.
I checked Amp this morning on the way in. It hovered around 20A for the first ten minutes of driving (heat on, radio on) then when I got on the freeway it went steadily down and did not go above 6A for the duration of the drive, about 30 more minutes. Voltage was pretty much the same as last night.
Have you used the heated mirror function since clearing the codes?
Isn't the code for the fuel filler cap having to do with it locking/unlocking the filler door? Does the door lock and unlock when using the key fob? I'm assuming it is if your getting gas.
Mines a 2010 and records show trans serviced at 40,000 miles, 80,000 miles and now its a little over 150,000 miles and Im just waiting for nicer weather to do it myself, along with replace the rusted trans pan. My Maintenance manual says it should be serviced every 40,000 miles.
Awhile back I was pulling into my parking spot in the back, i do a large half circle then back up into my spot which is on an incline. Soon as I stepped on the brakes to stop and put it in reverse it stalled, oddest thing. Hasn't happened again since. Maybe this was just an odd one time issue. few months ago my red battery light was showing on the dash, was driving me crazy trying to figure it out. hasn't happened since.
last thing, when you mention going down an incline im wondering how much gas you had in the tank, if it was very low maybe something with the fuel pressure, Im totally speculating on this one.
Yeah, I checked my records and it looks like the transmission oil was not changed at 120k when it was supposed to be. I'm at 133k now so may just have it done and test the battery while I'm at it.
02-20-2024, 01:37 PM
