Battery - Stop Vehicle Warning

[NickWal]

Hi. I purchased an E220 Cabriolet in January this year. In April, one morning the car just wouldn't start - it was a flat battery and the breakdown guy gave me a charge. I took the car back to the supplying dealer (not Mercedes) and he fitted a new battery. 2 minutes after leaving the dealer I had a red warning to stop the car, with a battery symbol (I had never had this warning before, even when the original battery was clearly on the way out). I took it straight back and the guy hooked up his diagnostic computer and said he hadn't cleared down one of the messages after fitting the new battery. I drove off again to go back home - about 200 miles. No issues at all. Stop / Start was working and it never had before, and a couple of other little niggles had disappeared.

A few days later I had it in Mercedes Liverpool on a recall notice. About an hour in they told me they had to replace the NOX sensors and they'd give me a call when they came in (free as part of the recall thankfully). I drove home and about a mile from home this red battery warning popped up. I arranged to go back to Mercedes the next morning. However, the next morning the message had disappeared. I drove it to Mercedes and still no message. They hooked it up and said everything was fine and that it may have had a voltage drop as a result of them having the car hooked up the previous day. I drove it home and no issues.

Now I've had the red warning pop up twice in the last 4 days, but it's gone again the next morning.

I can't fathom it. It's had a new battery, Mercedes didn't find anything in the diagnostics. Any advice?

The battery is reporting a voltage of 14.1 in the MercedesMe Adaptor app.

Thanks

 

[grober]

Might be your auxilliary/backup battery?

 

[davymead]

Next time it comes on, take a pic on your phone and take it back to Mercedes.

 

[markjay]

The voltage you see on the Mercedes me Adapter app when the engine is running is that of the charging system (alternator and voltage regulator), not that of the battery.

You need to check the battery voltage with the engine switched-off. If you don't have a voltmeter handy you can try one of the following:

Turn the ignition key to position I (one position before all the LEDs on the dash come-up). Make sure the LCD in the instrument cluster is showing the trip odometer (aka 'Standard Display'). Hold the 'answer phone' button on the right side of the steering wheel, then quickly hold down the OK button on the left side. Keep both buttons pressed for 10 seconds. When you get the 'Vehicle Data display, let go of both button and press the OK button until you can see the voltage.

This is what it looks like on mine, yours should be similar (the E-Class Cabrio A207 is based on the C0Class Saloon W204, which is what I have):

The other option is to bring-up the Cockpit display on the Mercedes me Adapter app with the engine running, then while looking the voltage display, switching-off the engine by turning the key from position II to position I, and quickly back to position II. The app will continue to show the voltage even without the engine is not running as long as the key remains in Position II.

 

[markjay]

Also, on a car equipped with AGM battery and Stop/Start, you are likely to see 12.4v (80% charge) at best.

This is because the Battery Management Module will charge the battery at a high rate until it reaches 80% capacity, and it will then only trickle-charge it for the last 20%.

But realistically, unless the car is driven for several hours each day, the trickle charging will never be able to get the battery to 100% capacity (12.7v). This is not an issue, this is by design.

If you do want to charge the battery to 100% without driving the car daily, you'll need to do this via a trickle charger, e.g. CTEK.

And, if trickle-charging, make sure you connect the charger to the charging poles in the engine bay, and not to battery poles directly.

This is because the Battery Management Module monitors the battery power input and output, and charging it directly to the battery poles will bypass the Battery Management Module and confuse it.

Incidentally this could be one of the reasons you're getting fault messages after replacing the battery. The correct procedure involves using STAR to save the battery parameters prior to the swap, and then reset the Battery Management Module once the new battery is fitted. If this is not followed, then this again can confuse the Battery Management Module because it is not expecting to find a new fully-charged battery out of the blue. That said, these issues usually resolve themselves after driving the car for a while, when the Battery Management Module eventually sorts itself out.

Also, if the new battery isn't a genuine MB battery, then check the model to ensure that it is the correct battery for your car, i.e. an AGM battery with the correct Ah / CCA rating etc. .

 

[markjay]

The recall and NOX issue could be the Dieselgate software update, you can search it on the forum, there are many threads here about this topic.

 

[NickWal]

The recall and NOX issue could be the Dieselgate software update, you can search it on the forum, there are many threads here about this topic.

Thank you for all the advice. I’ll try what you suggested to find out the battery voltage.

Yes, the recall was about diesel.

 

[NickWal]

Might be your auxilliary/backup battery?

Is there a way to check?

 

[NickWal]

The voltage you see on the Mercedes me Adapter app when the engine is running is that of the charging system (alternator and voltage regulator), not that of the battery.

You need to check the battery voltage with the engine switched-off. If you don't have a voltmeter handy you can try one of the following:

Turn the ignition key to position I (one position before all the LEDs on the dash come-up). Make sure the LCD in the instrument cluster is showing the trip odometer (aka 'Standard Display'). Hold the 'answer phone' button on the right side of the steering wheel, then quickly hold down the OK button on the left side. Keep both buttons pressed for 10 seconds. When you get the 'Vehicle Data display, let go of both button and press the OK button until you can see the voltage.

This is what it looks like on mine, yours should be similar (the E-Class Cabrio A207 is based on the C0Class Saloon W204, which is what I have):

The other option is to bring-up the Cockpit display on the Mercedes me Adapter app with the engine running, then while looking the voltage display, switching-off the engine by turning the key from position II to position I, and quickly back to position II. The app will continue to show the voltage even without the engine is not running as long as the key remains in Position II.

Hi. Here is the reading

 

[markjay]

12.6v is perfect.

Although 9.6A sound a bit high - I wonder what others are getting?

 

[NickWal]

12.6v is perfect.

Although 9.6A sound a bit high - I wonder what others are getting?

Thanks. Am I ok to ignore the stop vehicle message - will it do any harm if I do?

 

[markjay]

Thanks. Am I ok to ignore the stop vehicle message - will it do any harm if I do?

I can't say... given what you have described, if it was my car I would probably drive it. But this is just my personal choice.

 

[NickWal]

Faulty battery sensor. £260 to replace.