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Dear All,

For the last 3 years, I have been experiencing a persistent problem with my automobile that causes significant discomfort. Through careful observation, I have gathered some information that may assist an expert in making an informed speculation on the underlying cause of this issue. Essentially, on some occasions, the automobile fails to initiate, and does not even attempt to start when the key is fully turned to the right.

Car: S350 Bluetech, 2011 (W221)

Side note: When the vehicle successfully starts (which always happens, although sometimes after an hour or on the second attempt), all issues vanish and it operates well as expected.

Symptoms: -Ignition key turned to second position (just before turning the engine on), turning further wouldn't turn the engine on, not even a crank comes out.
-On the dash 2 mistakes pop up: Run flat inoperative, ESP Inoperative
-The engine cooler temperature doesnt move at all on the dash (even if the car has been running before and I am 100% sure it would be over 60-80C -The little coil sign (pre-ignition glow thingy) doesn't show up at all on the dash, even if the engine is completely cold -I can't hear the hissing sound of the compressor (for air suspension) so pretty sure that doesn't turn on either =Reading errors out, 2 peding one shows up: The error codes P0113 and P00AD indicate a problem with the Intake Air Temperature Sensor 1.

I have deduced that the issue is likely related to the battery voltage, given that it consistently occurs during winter and cold seasons. I have not seen it during the summer season. Additionally, it is an infrequent occurrence that typically happens only when the automobile has been recently in use and has reached a high temperature. Note that voltage is usually greater after a long drive (battery more charged)
- When my battery was exhausted (below 12V), it took me an hour to start the vehicle, twisting the key back and forth, praying, etc. Upon replacing the battery with a completely charged one, an error may sometimes occur. However, after attempting to start the engine 2-3 times, it is possible to successfully switch it on. Additionally, I once attempted to jumpstart the car using another running vehicle after 20 minutes of unsuccessful attempts to start it independently. Surprisingly, the car immediately began without any error appearing.

Now the problem is that even with a brand new, fully charged 95Ah AGM battery, I do get this error and periodic non-start issue.

Additionally, it is worth mentioning that when the key is switched to position 2, several consumers are activated. Air suspension compressor would start, pre-ignition glow, aircon air, etc. Upon observation, I have seen that the battery voltage decreases by around 0.5 volts, even without attempting to start the engine. Fully charge brand new battery installed shows only 12.5V, and once I turn the key twice, that 12.5 drops to 12.0 -It has happened a few times that I turn key to position 2, I do see the glow plug show up for a half sec/air suspension starting to hiss, than suddenlly these cut off, the error message appears on the dash and I can be sure that I won't be able to turn the car on at that point.

Could this issue maybe be attributed to a short-circuit or a similar electrical malfunction triggered by a component that is activated while the ignition is in position 2? And voltage lowers, some module malfunctions and consequently problems show up/car doesnt start? It is peculiar that the automobile consistently starts, however occasionally it may need up to an hour, or necessitate locking the doors and attempting again after a 20-minute interval.

I really value even speculative conjectures.

It is possible that the defective component is the ignition barrel, while the glow plug light issue might be caused by a blown fuse. I recommend checking all the fuses to see if any need to be replaced.

Damaged ECU caused by water? If the drains are obstructed at the base of the windscreen, water may overflow into the battery compartment, potentially causing harm to the neighbouring Electronic Control Unit (ECU).

Thank you for the prompt response! Is it straightforward to determine whether the ignition barrel is the cause of this issue?

Thank you, that may definitely be the issue since sewers were previously obstructed. Furthermore, this mistake occurred on at least two occasions while the vehicle's engine was warm, which is an uncommon occurrence. The first instance was immediately after I cleaned the car with a high-pressure water jet, and the second instance was after a prolonged drive in rainy conditions.

It is rather vexing that none of the garages, even those affiliated with Mercedes-Benz, inspect or clean the drains. It took me a considerable amount of time to discover that I must do this task on my own.

If the ECU is actually destroyed, will increasing the voltage still be effective in starting the vehicle and resolving the errors? Earlier today, I attempted to start the automobile and encountered the typical problem messages. Subsequently, I elevated the automobile using an additional battery, namely a three-year-old authentic MB battery that I had just replaced with a brand new one. As a result, all problems vanished and the car immediately began.

Additionally, is the voltage of my battery within the expected range? The battery is a new 95Ah AGM Varta, which has a little larger capacity than the one initially installed by MB. It is completely charged and had a voltage of 12.7V when it was fitted. After driving for a duration of 3 hours on the highway, the following morning the battery voltage is indicating a range of 12.2-12.3V. When I turn the key twice, the voltage decreases by 0.5V to below 12V immediately before I start cranking up the engine. This voltage drop occurs when all the consumers, such as the air compression and pre-ignition glow system, begin to operate.

I would really appreciate any suggestions for a reputable independent garage in London.

What voltage do you have on the batteries while engine running, should be about 14v, if not then battery not getting charged.

The voltage reaches 14.7-14.8V during engine operation.

It is unexpected to see a decrease in electrical potential on a recently acquired battery the next morning subsequent to a 3-hour operation. It may be advisable to use an ammeter to check for any parasitic current draw in the vehicle (use caution while doing so). It is important to note that automobiles often take some time to completely shut down. Ideally, one should observe a draw of no more than around 30mA when the vehicle is totally shut down.