csuengr

Last week, the brake lights quit working (all three) and the ETS and BAS/ESP lights came on. The ABS is on intermittently. Took it in to get it checked out and no codes were found. Last night I noticed the license plate light is on all the time now. It will only go out when you turn the lights on. So essentially the light is working backwards. It is going into the shop on Monday, but was wondering if there is anything to look at before then that might save me some money.

I should add that this is a 2002 ML320.

Maj. Dundee

Was any work performed around the left rear quarter panel? That harness controls brake lights and license plate lights.

csuengr

No work has been done there. It is an idea to look. The license plate light problem is indicative of a bad ground.

But shouldn't the BCM throw a fit about the non-functional brake lights? Or is the BCM not that advanced yet?

Maj. Dundee

The BCM as you call it, is actually the AAM but it has nothing to do with the brake lights.

The ESP/BAS control module is not getting a signal that the brake light are working, hence the ETS/BAS lights coming on.

csuengr

All Activity Module. That is sort of a fun name. I am used to GM/US made vehicles, hence the BCM nomenclature. I will look at that harness.

Maj. Dundee

Here is what you should do. Start the engine, turn the headlamps on, then test both contacts on fuse #9 for 12v.

Then have someone step on the brake pedal while you test fuse #15 for 12v.

csuengr

No voltage on either fuse.

There is 12V on one side of fuse #9 with engine and lights off.

csuengr

So, got the license plate light issue resolved. This is my moms car, and my dad had switched relays 5 and 6, so the NC relay was in the socket for the license plate light. Still no brake lights, and the BLS has been replaced.

Maj. Dundee

Did you replace the BLS because of this problem?

csuengr

Yes. Other than fuses, it is pretty much the easiest and cheapest fix, if it works.

Maj. Dundee

Please follow the instructions in the PDF. Remove the switch and pull out the actuator pin as far as possible. Step on the pedal and install the switch. Then pull up the brake pedal and it will be properly set. If there are still no lights, see below.

OK, go to the BLS, turn the ign. to pos. #2 or start the eng.

Without touching the pedal, test the GREY and WHITE wires for 12v.

Then depress the pedal and test the BLUE wire for 12v.

Make sure the correct relay is in its place.

csuengr

Have 12V at white and grey. Have 12V at blue wire when pedal depressed.

Maj. Dundee

Then is has to be the K6 relay (special NC) or a wiring problem. Who knows what happened when your father switched relays, since all the other relays are NO.

1. ign off remove K6 relay.

2. turn key to pos. #2

3. have someone step on brake and test slot 30 and slot 87 for 12v.

4. then test slots 85 and 86 and tell me which one is GROUND and which one is 12v.


The slots in the fuse box have one or two silver contact points that must be touched to get a proper reading.

Get a heavy gauge wire stripped at both ends and insert one end touching a silver contact and test the other end.

csuengr

On K6, terminal 30 and 86 have 12V.

Does K12 do anything?

The brake light issue existed before the relay swap.

csuengr

Okay, the brake lights work now. I pulled the K6 relay, bench tested it. It worked fine. Jumped terminals 30 and 87a in the fuse box, lights worked. Put the relay back in, lights worked. Started engine, tuned steering wheel lock to lock and BAS ESP light went out.

Fixed it, somehow.

Thank you for all the help.

Don