M&S lights

**Tins** · 10th November 2023, 02:57 PM

Two days ago I came out and started to drive off, cold. Sluggish take off, Sure enough, M&S limp home mode. In the past, different trans, a simple switch off and restart would clear this. Not this time. Out with the Nanocom, fault was "position switch" something. I'm assuming a slight maladjustment of the XYZ. Ok, look at that later. No issues since, until, after a visit to the doctor, M&S are back. Same, won't clear with the key. Nanocom says "Check watchdog". Clear fault and all is well.
I haven't had a dog for years, so I'm assuming it's telling me something. Is this code for check the oil level or something. I haven't seen this one before.
History tells me to worry about 4HP22 issues.

**Tombie** · 10th November 2023, 06:16 PM

How long since driven. How’s the battery?

**shack** · 10th November 2023, 06:37 PM

A Watchdog fault is theoretically the TCU failing.

Position switch fault would be the XYZ switch.

It could be battery condition as Tombie pointed out, it's a bit hard to test though.

If you start the car and it has the fault, if you then clear it with the nano while engine running, the fault will must likely disappear and not come back until you restart.

Unfortunately this is not necessarily an indication that it's the battery at fault.

I'd try a different battery, if that doesn't work swap the TCU If you can lay your hands on one easily.

I wouldn't drive it far with the MS lights flashing though, good way to cook the auto... Short drives should be ok, but towing would be very bad.

**Tins** · 10th November 2023, 06:43 PM

Originally Posted by Tombie

How long since driven. How’s the battery?

Driven daily atm. Battery is a little undersized for the car but is usually fine, although I did have a parasitic draw up until a week ago which I traced to the display illumination of the radio. Nano shows batt at around 14v.

**Tins** · 10th November 2023, 06:47 PM

Originally Posted by shack

A Watchdog fault is theoretically the TCU failing.

Position switch fault would be the XYZ switch.

It could be battery condition as Tombie pointed out, it's a bit hard to test though.

If you start the car and it has the fault, if you then clear it with the nano while engine running, the fault will must likely disappear and not come back until you restart.

Unfortunately this is not necessarily an indication that it's the battery at fault.

I'd try a different battery, if that doesn't work swap the TCU If you can lay your hands on one easily.

I wouldn't drive it far with the MS lights flashing though, good way to cook the auto... Short drives should be ok, but towing would be very bad.

I have a spare TCU. If it persists I will swap it.

Don't worry, after my experiences with autos in this car it doesn't get driven with them on at all. The fault clears and only has come back once, i.e. not every restart.

But, the batt is too small, the good one is elsewhere. I'll try to remedy that soon, but it has had this batt in it for months.

**Tins** · 11th November 2023, 12:48 PM

So, is the TCU plug and play, or do I need to do some nanocom trickery?

**discorevy** · 11th November 2023, 02:32 PM

Plug and play, but be careful with the connector

**Pedro_The_Swift** · 12th November 2023, 05:44 AM

As you know Tins.. Over the years M&S lights have nearly always been battery connected, before pulling the pin on a 1000cca CatBat, charge it properly overnight and check for parasites..

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