MGF/TF EPAS

DESCRIPTION

Steering power assistance is provided by an electric motor mounted on the steering column which drives the column through a worm gear arrangement. The level of steering assistance is governed by the power output of the motor. The EPAS ECU controls the current to the motor and hence the level of steering assistance. The EPAS ECU measures the steering column torque input from the driver and the road speed of the vehicle, supplying the motor with current to achieve the required level of assistance.
The motor is connected to the column via an electromagnetic clutch which is controlled by the EPAS ECU. If the EPAS ECU detects a fault in the system, the motor will be disconnected from the column by disengaging the clutch. The steering reverts to a normal unassisted system with the clutch disengaged.
The driver steering torque input and direction of torque is monitored by a sensor mounted on the steering column. The sensor measures the angular displacement of a torque tube. Outputs from the sensor are processed by two independent systems, these readings being compared by the EPAS ECU for accuracy. A difference in the two calculated values indicates a fault. The road speed signal, from a speed transducer on the gearbox, is also processed by two independent systems.

OPERATION
Power supplies
Power for the EPAS motor is supplied from the in-line EPAS fuse to the EPAS ECU on a brown wire.
Fusible link 4 in the under bonnet fuse box supplies battery power to the ignition switch on a brown-purple wire. When the ignition switch is in position II, the power is fed to fuse 1 in the passenger compartment fuse box on a black-yellow wire. Fuse 1 supplies the feed to the EPAS ECU on a green wire. A system earth is provided by a black wire connected between the EPAS ECU and an earth point.

General
When the ignition switch is first turned to position II, the EPAS ECU performs an integrity check to ensure that the system is operating correctly. During the integrity check, the EPAS ECU earths the pink-blue wire from the instrument pack to illuminate the EPAS warning lamp. The warning lamp remains illuminated until the EPAS ECU receives an engine speed signal from the ECM on a white-black wire. The road speed signal is transmitted on a white.orange wire from the speed transducer to the EPAS ECU . The EPAS ECU outputs a 5 volts supply to the torque sensor on an orange wire and connects the orange-yellow wire to earth to complete the circuit. Two independent torque signals are input from the torque sensor to the EPAS ECU on the orange-blue and white wires.

NOTE: Although installed in the harness, the blue-green and orange-white wires are not used.
When, from the torque sensor signals, the EPAS ECU detects a steering input, it switches the supply from the in-line EPAS fuse to the EPAS motor. For a right turn, the supply is switched to the brown-blue wire between the EPAS ECU and the EPAS motor , and the brown-red wire is connected to earth. For a left turn the polarity is reversed. The EPAS ECU regulates the supply to the EPAS motor between approximately 0.5 and 12 volts, depending on the level of assistance required.

The clutch in the EPAS motor has a power feed from the EPAS ECU on a blue-slate wire. The earth side of the clutch is connected to the EPAS ECU by a blue-pink wire. The EPAS ECU continually monitors the performance of the system. If a fault is detected, the EPAS ECU energises the clutch, to disengage the motor drive from the steering column, and illuminates the EPAS warning lamp in the instrument pack; a fault code is then stored in the memory of the EPAS ECU and the steering operates without power assistance. Fault codes can be read using TestBook, which communicates with the system on the pink wire connected between the EPAS ECU and the diagnostic socket . For certain faults, the EPAS ECU may temporarily reduce power to the motor instead of disengaging the clutch.

Possible causes for clutch disengagement or reduced power assistance include, (beside of a possibly blown 70 Amp Fuse):
- electric Motor overheat -
Repeated turning of the steering wheel from lock to lock causes a temperature build up in the EPAS motor. The EPAS ECU monitors the power supply to the EPAS motor and, if the level of EPAS motor activity will cause an unacceptable temperature, reduces the current of the power supply. Reducing the current of the power supply limits the power available for steering assistance and prevents permanent damage to the EPAS motor.
- Engine racing -
If the engine speed is in excess of 2500 rev/min for 30 seconds and no vehicle speed is detected, the EPAS ECU suspects a fault with either the engine speed sensor or the road speed sensor. The EPAS ECU then disengages the clutch and illuminates the warning lamp. If the vehicle subsequently moves off and a road speed signal is received, the warning lamp is extinguished and the clutch engaged.
- Low battery voltage -
If the battery voltage is below 8.4 volts, the clutch will be disengaged and the warning lamp illuminated.
- Poor power supply -
A fault in the power supply to the motor may produce poor steering feel. Low battery voltage may cause steering wheel loads to increase as the assistance is impaired. Fluctuating voltage due to poor battery condition or an alternator fault may cause torque fluctuations to be felt through the steering wheel.

Hi All,

Please read all before replying - sorry its a bit long.

First a bit of background - for the past 18 months my '99 MY2000 MGF has suffered from the now becoming rather common EPAS (electronic power assisted steering) bias where, when going slowly the steering wheel will turn to the left on its own quite dramatically. A way of proving this problem is evident is to raise the front of the car on a jack and then switch the ignition on - the steering will obviously turn to the left.

At my last but one MOT (March 2005), ATS failed it on this problem (it IS an MOT failure issue) and only when the MGR dealer wrote a letter would ATS agree to pass it but weren't happy to. After discussing it with the MGR dealer, B&G and MGOC they all said the only way to fix it is to replace the entire steering column - at a new part cost of £800 or a second hand part cost of less if you can find a second hand one from ebay or a breaker - you are then looking at fitting it yourself.

Another way of fixing it is to visit a man called Alan - a specialist in power steering. He has ised on here before and on eBay but had a few negative comments in return. I was happy to ignore these and so this is the method I chose. I visited Alan a couple of weeks ago with only his word over the phone that he could fix it in a couple of hours.

Well, after a couple of hours of my MGF being with Alan it is now perfectly fixed. It is now a delight to drive again - I no longer have to hold on tight to the wheel at all times while driving slowly. It was a pleasure to talk to Alan about the problem and the history behind it - an easy to get on with person who, yes although earns money from doing the fix, clearly wants to help where he can. He was also extremely flexible at when he could fit me in.

As with the majority of issues with MGFs such as head gasket failure, suspension problems, gear linkage cables snapping and simpler tasks such as replacing brake pads, oil changes etc I'm fully aware there are instructions out there on how to perform these jobs as DIY and some mechanically minded people are happy to follow these to fix them. However there are also a lot of people who lack the ability or confidence to do it themselves - these are the people who visit garages instead. I don't know of any of the normal MGF specialists (MS, MGFC, B&G, MGOC etc) who will do the EPAS fix as above without going down the costly route of replacement parts. So I'd very much recommended a trip to see Alan as a much cheaper alternative to solve the problem.

So, finally to pass on Alan's details - give him a call and discuss it with him:

Telephone: 07971 420682
Email: quoman_bigg@[NOSPAM]ntlworld.com (remove the [NOSPAM] part to send an email to him)

If you have any questions for me personally on this, please PM me - more than happy to help.

Thanks for reading and regards

ChrisT.
Posted 19 May 2006 at 09:31:18 UK time
David Clelland, http://www.csmgf.co.uk

Yes that's all very well Chris, but how much did Alan charge you for fixing your EPAS?
Posted 19 May 2006 at 09:57:34 UK time
Ted Newman, Royal Arsenal, London

David - good question! BUT I would guess a lot less than than having a new column fitted!
Posted 19 May 2006 at 12:19:50 UK time
Carl, Sweden.

And the more technical part of it : What is the reason for the need of "re-aligning" the pot? Could it be a ageing problem of the cermet track on the potentiometer? Wear on that track due to the moving slider? Most probably there is no permanent fix,in due time it will pop up again if it is based upon wear.
Just wonder if that pot can be found at any electronics part dealer at a fraction of cost for a new steering column.
Posted 19 May 2006 at 12:28:46 UK time
darren jeffery, milton keynes bucks , darrenjeffery@yahoo.co.uk

Did you check out rob bells and keith starbucks way to mend the epas steering. i did mine it saved me mega bucks i think you where done there chris sorry mate ..

darren jeffery

theres a page on robs site how to save money mr starbucks info and me check it out
Posted 19 May 2006 at 13:11:33 UK time
Chris Tromans, Cambridge, UK

Darren,

Take another read of the post - as mentioned in para 5 ("As with the majority...." - I'm fully aware of Rob and Keiths instructions on how to fix the epas steering but my report was simply intended to point out that, for those who are not confident at all of carrying out this task (similar to those who don't carry out their own HGF repairs) they need to be aware of specialists who can carry out the job for them.

My wish was to make people aware that Alan is a specialist on this and is very capable of completing the fix (yes, at a cost) and is a good friendly bloke who's there to help people. This is in a similar way to many people posting that the MGF Centre (for example) did a cracking job on an HGF repair for them (but again, at a cost).

Hope this is understood. Essentially, those people who do pay specialists to complete work should not feel they have been 'done' because they don't have the abilities themselves.

Cheers

Chris
Posted 19 May 2006 at 13:43:22 UK time
Ted Newman, Royal Arsenal, London

With any safety related item it is far better to have an expert do the job if you are not confident in doing it yourself.

And I should like to thank Chris for bring it to our attention that there is guy available to do it for us.
Posted 19 May 2006 at 14:33:20 UK time
darren jeffery, milton keynes bucks , darrenjeffery@yahoo.co.uk

Sorry chris for running off i see your point now.. argh that goes to show you should read things first before typing argh.. wasnt havent a dig at you honest. And thanks for the number matey. As you said some people have confindence to do things and others dont .

cheers mate no hard feelings

darren
Posted 19 May 2006 at 15:28:22 UK time
Chris Tromans, Cambridge, UK

Hey Darren,

Absolutely no offence taken :-)

Chris
Posted 19 May 2006 at 15:42:52 UK time
alan bigg, west wickham, quoman_bigg@ntlworld.com

thank you chris for your very positive response
i am glad that you didnt feel "done".i would also like to thank ted for his positive statement i hope to deal with some of you very soon!!
Posted 19 May 2006 at 16:12:34 UK time
darren jeffery, milton keynes bucks , darrenjeffery@yahoo.co.uk

hey chris did mine in the end remember last year???mine passed but still steering left they said i would need a new rack. well i done mine just moved the sensor and bingo job done,,, has not moved since

darren

Posted 20 May 2006 at 18:58:39 UK time
Roger Parker, Tamworth/Swavesey, RogerP@mgownersclub.co.uk

Adressing this problem has until the arrival of those prepared to tackle repairs been a complete column replacement at a new cost of well in excess of £600 plus fitting plus vat.

Of those who have had the repair done I have not had any negative feedback of recurring problems, and then if the steering does develop the bias again then it would be a matter of further adjustment and you would have to suffer around four repeat failures before even getting to the cost of a standard repair.

In addition to the services offered by those based in the Greenwich area of London, MGOC Workshop is able to offfer this repair service for a very competitive price (ring 01954 234001 for more details) and would be more convenient for many over the location of other current specialists offering the same service.

I expect that as more specialists start to offer such a service in more locations the price will drop some more with that growing competition.

Rog
Posted 20 May 2006 at 19:59:38 UK time
mike

Chris, we have been fixing the EPAS bias for well over a year by adjusting the bias, we ususlly alow 1-2 hours labour.
Posted 22 May 2006 at 09:09:58 UK time
alan bigg, west wickham, quoman_bigg@ntlworld.com

my price for this job is £95 to people who mention this site
Posted 22 May 2006 at 11:00:44 UK time
Chris Tromans, Cambridge, UK

Mike, Roger...

Thanks for correcting my post in that others are already doing this work. Roger - I've had my F serviced at MGOC for the last two services - it had the problem last year at my service and you didn't mention it was fixable by yourselves so thats why assumed you still didn't. Mike - I just didn't see it on your online price list so again, assumed you didn't. My mistake.

I guess for those near and around London, Alan is the quickest to get to :-)

Chris