Thread: M and S lights flashing on dash.

Originally Posted by Skimmo

What causes this to happen intermittently. They reset when car restarted. When lights flashing together the car loses power.

It is usually triggered by a CAN communication error or by the battery voltage dropping below 9 volts when starting the car.

If you restart after the battery has charged a bit and it is ok, that would suggest it's the battery voltage that's causing it.

When the M & S lights flash, the auto ECU will adopt a "limp home" strategy with the modulator pressure to max and 1st and 2nd gear will be ignored, the auto will be locked into either 3rd or 4th depending on the scenario, that's why it seems to have no power.

There are numerous other reasons for the M & S lights, but those are the most common.

Cheers
James

Thanks James. The battery is new and fully charged. Any other possibilities. I have read that a faulty switch on the auto trans can cause this to happen.

Originally Posted by shack

It is usually triggered by a CAN communication error or by the battery voltage dropping below 9 volts when starting the car.

There are numerous other reasons for the M & S lights, but those are the most common.

Cheers
James

True.

If, on the other hand, they come on when you are driving normally get the auto checked. I did not and the auto failed. Not instantly, but the M & S lights in my case were a warning that I ignored, as they went away with a restart so I assumed gremlins.

Good advice. I’ll get the switch on the gearbox checked (someone called it the xyz switch I think). If not faulty I’ll get the trans looked as well. It doesn’t happen when I’m on the move driving say on the freeway, but usually flashes when I drive out of the driveway ie start then stop prior to getting getting into general road mode.

Originally Posted by Skimmo

Good advice. I’ll get the switch on the gearbox checked (someone called it the xyz switch I think). If not faulty I’ll get the trans looked as well. It doesn’t happen when I’m on the move driving say on the freeway, but usually flashes when I drive out of the driveway ie start then stop prior to getting getting into general road mode.

The XYZ switch is expensive, but there are a few threads here about repairing them. Also, there can be an issue where the wiring going over the trans will chafe, which can cause issues.

Shack is a lot smarter than me when it comes to the electrics on these things, but it's worth following this up. The warnings were put there for a reason, so if they persist it's good to find out why.

If it is the XYZ switch, which is probably the next most likely culprit, you can sometimes avert the issue by parking the car so you can take off in drive in the morning, then moving the selector into neutral before turning the key on to start, once started in neutral, move into drive and see what happens.

I know that's a ridiculous procedure, and that no one should ever know that it might work... But here we are!

As Tins said, the M & S lights should not be ignored, they are happening for a reason, it's necessary to find out why, someone with a nanocom might be able to help read the fault codes.

If you drive for extended periods or tow with the lights flashing, you will have a fairly sick auto pretty quick.

Cheers
James

If I go from drive to reverse to quickly the m&s lights go off been like it for a long time now, it’s on the list

Here's a simple test for the switch if you don't have a reader.

ignition on in Park, engine doesn't have to be running, slowly move through R,N,D,3,2,1 while observing the dash readout, if you see blank screen between any of them, especially if the M and S lights start flashing, then it's XYZ replace / refurb time.