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MG MGF Technical - MEMS Unit reset

Hi

Me again!

Pardon my ignorance - does a MEMS unit reset have to be done by a dealer or is it something I (or rather my hubby) could do? If so - how's it done?

Sorry if this is a daft question.

cheers

Eileen
Eileen Barker

Eileen, I'm sure I've seen mention of this in the archive but no idea when/where.

You need somebody like Bruce or Dieter or Will to switch on their PC and gallop to the rescue.
JohnP

Eileen,

Not sure what you mean by a MEMS unit reset but I presume from your recent thread on Flat Battery it is in connection with that.
The MEMS unit is a computer in the engine compartment of your car and can probably 'crash' at times just like your desktop computer. To reset it would just entail removing the battery earth for a few minutes and then reconnect it. However, I have never heard of any MEMS units 'crashing' before. Rover dealers have what is called a 'Testbook' which is a computer that can interrogate the MEMS unit and associated circuits to find problems and reprogramme things like the Alarm ECU etc.

The flat battery problem has in the past been blamed on the MEMS Relay unit which is a box of, you guessed, relays next to the MEMS unit in the engine compartment. It has been noted by some owners, myself included, that very occasionally the MEMS Relay unit sticks on. Let me explain.
When you switch off your engine the MEMS unit keeps the power switched on to the engine bay fan and other things as well. This allows the fan to operate if need be after you have stopped the engine, thus cooling the engine bay. There can be a large increase in temperature when the car is first stationary and the engine has no cooling by the normal method.

After nine minutes or so the MEMS switches of the relay and the current drain on the battery drops to its minimum. Some people have found that the relay is still on after days and the battery is approaching flat. Whether this is caused by the computer staying on or the relay sticking has not been established (to my knowledge). It is possible also that the battery going flat may cause the MEMS to malfunction and switch on the relay thus worsening the problem. I am trying to find an answer to the cause of this problem myself. My car is wired up with various LEDS to indicate what's on etc after switching off the ignition.

Well, all this doesn't really help you because perhaps this is not the answer to your question?

It depends on what you mean by resetting the MEMS.

cheers

Bruce
Bruce Caldwell

>Some people have found that the relay is still on after days and the battery is approaching flat. Whether this is caused by the computer staying on or the relay sticking has not been established (to my knowledge).

The time until the relay should get switched depends on engine temperature.
If cold then its up to 3/4 hours. If warm it's 3 to 5 minutes only.
Longer times like the mentioned *days* direct to a broken ECU. Unfortunately no reset will help. A sticking relay is another case as mentioned by Bruce.

A so called MEMS reset may be required only after engine repairs is said to be possible with 'Testbook' only.

May be you reffer to the Steppermotor reset ?
This is ignition on to the affiliated ignition lock position. Then 5 times key the accelerator. Turn ignition key back and pull out. Then start as usual.
Dieter K.

Hi Dieter,

Can you explain further
<<The time until the relay should get switched depends on engine temperature.
If cold then its up to 3/4 hours. If warm it's 3 to 5 minutes only.>>

Do you mean that if, from cold, I switch on my engine and then turn off again the relay will stay on for hours? To what purpose? I've timed mine to be about nine minutes when hot but never checked from cold.

cheers

Bruce (still no job)
Bruce Caldwell

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Bruce Caldwell

This thread was discussed between 02/02/2003 and 04/02/2003

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