I intermittently get the fault code P056200 low voltage on the brake booster module according to my OBDeleven.

According to the OBDeleven website it says “This code is a big red flag - you shouldn't drive your car when this appears.”

Is that statement an over exaggeration or is this something that needs immediate attention?

I've had that and a host of other faults pop up today, electric park brake, auto hold, lane assist, front assist, SOS...

Did you apply an OTA application update a couple of days ago by any chance?

25 minutes ago, scotthugh3s said:

I've had that and a host of other faults pop up today, electric park brake, auto hold, lane assist, front assist, SOS...

Did you apply an OTA application update a couple of days ago by any chance?

No. I think the reason i get the fault code is that my battery isn’t the freshest.

7 minutes ago, Micky 32 said:

No. I think the reason i get the fault code is that my battery isn’t the freshest.

Yep, I'm actually thinking the same thing. I was sitting in traffic behind and accident today, and left the engine running for the blowers as it was really cold out. Parked up shortly afterwards then when I got back in is when these pinged up.

Gonna connect my charger tomorrow and hopefully that sorts them

1 hour ago, Micky 32 said:

I intermittently get the fault code P056200 low voltage on the brake booster module according to my OBDeleven.

According to the OBDeleven website it says “This code is a big red flag - you shouldn't drive your car when this appears.”

Is that statement an over exaggeration or is this something that needs immediate attention?

If it is a genuine fault indication, I'd say definitely yes - I'd have thought that driving with any braking system fault that could result in sudden loss of braking force would be a no.

I once tried rolling a vehicle down a gentle slope with the engine off, and was shocked at how I literally had to stand on the brake pedal with full weight to get any braking - this was at less than 2MPH!

The very first thing to do if odd, and sometimes seemingly random errors are indicated on these vehicles should be to give the battery a through test, including at a high load.

1 hour ago, Warrior193 said:

If it is a genuine fault indication, I'd say definitely yes - I'd have thought that driving with any braking system fault that could result in sudden loss of braking force would be a no.

I once tried rolling a vehicle down a gentle slope with the engine off, and was shocked at how I literally had to stand on the brake pedal with full weight to get any braking - this was at less than 2MPH!

The brakes seem to work fine regardless of the code. I’d say my battery just isn’t as good as it should be despite it being only 19 months old. Performs ok ( cranks fast and start stop works ok) but cranking voltage can drop below 9.6v at times.

Edited 17 January17 Jan by Micky 32

9.6 volts is too low and is a strong indication the battery is failing.

What is the charging voltage?

Total failure can be sudden and leave you stranded.

At the very least, you will be chasing phantom fault warnings - remember what happened to the Boy who called Wolf once too often.

The Mk4 needs the battery to be in peak condition, it doesn't take much of a drop to cause random codes. Obviously, ignoring codes is a potentially dangerous practice, so you're always obligated to check them out and determine whether genuine or phantom. About 12 months ago I started the habit of connecting my smart charger when the car isn't in use for more than a few days, since then I've never had a code appear.

2 hours ago, Warrior193 said:

9.6 volts is too low and is a strong indication the battery is failing.

What is the charging voltage?

Total failure can be sudden and leave you stranded.

At the very least, you will be chasing phantom fault warnings - remember what happened to the Boy who called Wolf once too often.

The lowest i have seen is 7.96v.

12 hours ago, Micky 32 said:

The lowest i have seen is 7.96v.

I mean what is the alternator output? - measured at the battery terminals with the engine running.

A voltage as low as 7.96 is far too low under any conditions - was this while the engine was being cranked? It is little wonder that fault codes (DTCs) are being thrown!

The alternator is charging fine. The brake regeneration works now and again but it seems to constantly charge the battery mostly 14.5-14.9v. The cranking voltage readings i get are from a bm2 battery monitor and a Topdon battery tester.

Which instruments will presumably be flagging that the battery is failing and should be replaced?

If that battery is only 19 months old, is it still under warranty? If so, I'd be looking to submit a claim on it.

Edited 18 January18 Jan by Warrior193
added information

5 hours ago, Warrior193 said:

Which instruments will presumably be flagging that the battery is failing and should be replaced?

If that battery is only 19 months old, is it still under warranty? If so, I'd be looking to submit a claim on it.

A test i did today. “ replace”. The strange thing is if i didn’t do any tests or diagnostics i would never suspect a failing battery. Cranks fast and starts quickly and the start stop works perfectly.

I suspect it won’t be easy to get replaced under warranty if the car starts ok etc.

Edited 18 January18 Jan by Micky 32

The 55% health is only part of the story though - the voltage dropping through the floor while the engine is being cranked will be what is causing apparent spurious DTCs.

That's pretty bad for a battery less than 2 years old!

Internal resistance is fine, so that's not the problem.

Can you show a cranking test result on that too?

A couple of low ones via the BM2 over the last couple of months. I constantly get ‘U’ data bus codes etc

Edited 19 January19 Jan by Micky 32

On 19/01/2026 at 14:50, Micky 32 said:

A couple of low ones via the BM2 over the last couple of months. I constantly get ‘U’ data bus codes etc

What's the app you're using in those screenshots please?