tgeej

I have been getting occasional codes and occasional engine and shifting behavior that causes me to suspect my ECM. Before springing for a replacement ECM . . . I have seen a couple of videos describing disconnecting the battery and then grounding the positive cable for a number of minutes in order to drain residual voltage from the ECM (and other modules) to restore original parameters, and maybe correct any faults. Of course, I wonder if anyone has any thoughts, suggestions, or experience with this procedure.

CaliBenzDriver

The ECU gets rebooted everytime the key is cycled On/Off. Dumping learned data is a step backward, not a fix.

Disconnecting the battery reboots the SAMS. This helps prevent them from draining the battery when they fail to enter low power mode.

What sort of fault codes are causing you problems?

Many conditions can cause the ECU not to run the engine/tranny as best as possible. Kudos to you for recognizing degraded modes. Many people are satisfied when the engine simply runs.

What sort of troubleshooting steps have you done so far...?

tgeej

Thanks for your quick reply and insight. With all the complexity of this car I have been leery of trying that. I have disconnected and reconnected both batteries. It all started with simultaneous P0030 and P0050 Ox sensor no heat right and left side. Next P2176 Idle position not learned. Next P2240 Ox sensor discrepancy and P0300, P0301, P0302 Random, Cyl 1, Cyl 2 misfire. The most bizarre then being P0040 Ox sensor signal swap. I have not even touched the sensors or the wiring. Over the course of the last month or so the car will run fine for a day or more, then an acceleration or obvious misfire situation becomes apparent. Shutting down and restarting usually restores normality, or after normal temps are reached and a hard acceleration. Thanks again.

Festushagan

Wow, Almost exactly the same problem with my 2009 c300 with 66,000 miles on it. I also have a P0607 and an alternator serial interface fault. Always garage kept and rarely sees rain or snow so i dont think it is the common water leak problem. Hope someone replies with some clues. Trying to avoid the dealership for obvious reasons. Thanks!

CaliBenzDriver

That's a lot of headaches at one time... take a good look at the ECU connector and harness for traces of ENGINE OIL.

Are there any other CAN modules reporting faults or missing besides ECU crazy O2 handling?

tgeej

Thanks, yes I've checked the ECU connector (pins, harness, etc). No other faults.

CaliBenzDriver

You have got yourself an interesting case of non-standard random failure


It is all closely related to ECU, nothing remote. It can clear with a restart and not always stay bad.

Fuel supply pretty unlikely because of that code for O2 swapping.

Reported check NO "oil in harness" here.

Next....:
> Check running voltage is around 13.7V when this happens

> Inspect/clean every ECU groundings to both engine and chassis.

There are not many clues to go after. Do a good job here else car may be inching closer to trade-in lot.


​​​​​​

Festushagan

Hey, Going to inspect my grounds also, Was poking around underneath my 2009 c300 with similar issues and did a test at idle and a previous test indicated one of my 02 sensors was not functioning but now it is functioning. Also have a mild transmission leak. Idle still seems low and there is no change in rpm when i turn on the air cond. Going to erase all codes again and check to see what comes back! Last ditch effort is to disconnect battery and check the ecu connections. Thanks for all the info!

CaliBenzDriver

don't dump the DTC without letting us know what's on that list. Ppl keep hoping enough reset will bring joy.... nop! Got to make sense of as many clues as possible.

O2 are most important for ECU to adjust the injected mixture. They are well built not to quit even long after they should have been renewed. Anything O2 and ABS/ESP is seriously designed well.
That is not to say they don't get baked or never get from "oil in harness".
You can focus on that to

Festushagan

Hi, Still have the original OBD2 codes written down and the MB faults in the ecu written down. So the wiring harness inspection will continue! I am hoping to discover something obvious because an unrelated issue i had with another vehicle caused me to be apprehensive about dealership repairs. They part swapped me till i warned them the money spigot was drying up. Later the same electrical problem appeared so i set my mind that i was going to fix it and discovered a wire for the keep alive memory in the ecu had a loose crimp and the wire slid out. Solved the issue with a good old multimeter!