Vauxhall/GM EPAS power steering details

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Vauxhall/GM EPAS power steering details

Post by badlyworntoy » February 16th, 2012, 6:40 pm


As requested Here are some details on the GM/Opel/Vauxhall Electronic power assisted steering (EPAS) power steering retro fitted to my lada.To those who don't know this is a motorised steering column which is triggered to assist when torque is applied via the steering wheel
I though maybe we could do this as a post as it may well intrest other people,I've been asked about it on numerous occasions.

This a rather new system fitted to Corsa B and C models from 2003 onwards A similar system is fitted to Fiat Puntos,but this isn't as good as GM version as its only designed to assist the steering for parking and is switched on and off via a button on the dash. It also generally isnt worth using as its not an easy unit to disassemble for modification (i've had a good look at one). Electronically the GM system uses a engine speed signal and a gearbox speed signal to regulate the tension of the Column. When we retro fit it to our cars we must use a aftermarket control unit which tricks the unit into thinking it has these signals. You can then adjust it with a twiddle knob which you can mount anywhere on your dash board. I've discovered that when you drive at high speed the steering can be very twitchy and its best to turn the unit off but at lower speeds its great. A chum of mine fitted one to an old Series 2 ex army Land rover but as the unit was getting worked hard off road it seemed to overheat and kept cutting out,they don't seem to lend themselves well to off road vehicles which is a real shame.

I wouldn't recommend you fitted this to any car unless you have very good skills with welding, machining and fabrication as its very involved no 2 cars are ever the same,In most cases you have to strengthen the Bulkhead column supports and adapt the pedal box. I've fitted these several times to various cars,Lotus esprit and Humber Sceptre to name a couple of recent ones and its always been a hard but worth while modification..
You can fit these 2 ways,the easy way is to retain the Corsa Column switches,ignition lock. You then must change steering wheel for GM one,This may look silly on an Old/Retro car and doesn't give a good look, you will also need to do extensive modifications to your wiring harness to make this work. They is advantages to this though. You get a modern steering lock and a very good quality ignition switch I did it this way in the Lotus esprit but because its a more modern sports car, GM switches and ignition lock cowling don't look so bad but In my 1965 Humber they look silly.
The other way to do it is to totally remove the corsa column and modify and adapt the one from you modified car. This requires joining the two column shafts together and for this you need a precision machined joint professionally welded together.

If you notice in the lada application the column looks very long this is because the unit physically is too big to fit in the desired gap,But in this application with bucket seats we want a longer steering column anyway bringing it closer to the driver so it works very well.

Its also worth noting that I pay around £80-£100, this is generally the going rate for a second hand unit no more than that. you must also get the brown and blue plugs from the corsa wiring loom to power up the unit.

Have a look at the pictures and give your honest opinion
epas 1.jpg
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epas 2.jpg
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epas 3.jpg
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epas 5.jpg
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epas 10.jpg
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epas 11.jpg
this is the lada pedal box and suppport modified using vauxall/lada parts
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epas 12.jpg
Lada modified pedal box
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epas 13.jpg
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Re: Vauxhall/GM EPAS power steering details

Post by Walezy » February 18th, 2012, 8:24 am

What have you used to make the speed sensor signal? I got for my Fiat 131 quaife sequential 6 speed gearbox and this unit does not have speed sensor which is required to run honda f20C(s2000) engine properly - i have this engine in my Fiat. I need to make the ECU think it still has the speed sensor running(simply connecting the sensor is not good enough, it needs to show speed)

Guy Croft
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Re: Vauxhall/GM EPAS power steering details

Post by Guy Croft » February 18th, 2012, 9:58 am


Nice work there Ian on the power steering - I know how time-consuming it is to form a decent article.

Thanks very much for publishing it here,


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Re: Vauxhall/GM EPAS power steering details

Post by Boyracer » March 5th, 2012, 11:18 am

I am adapting 1st gen Toytota MR2 electric power steering pump to be used with stock BMW steering rack. I have to get rid of belt driven pump to make room for oil filter/cooler pickup plate.

It is basically normal power steering pump that is run by decent sized 12 v DC motor. Normally it is controlled by dedicated unit that decides load but since I don't have that I am making the control box myself, a microcontroller and few MOSFET's to drive the pump. Pump has two ports, low pressure fluid in from reservoir and high pressure to steering rack. Quite same as OEM pump so fitting should not be a problem, you only need to make bracket for pump and some new hoses.

Basically the control box takes speed signal from normal ABS sensor and rate of steering wheel rotation from optical encoder fitted to steering column. Based on that microcontroller decides how much pressure is needed from the pump and then it adjusts it by using pulse width modulation, it is bit like taking RPM and load signals to calculate how much fuel you need to inject. This should work well (people have run these pumps without any load adjustment, basically 100% all the time) but optimal would be to get torque from steering column but since that is not possible I have to take the rate of rotation. I think also cockpit mounted adjustment knob for overall effect would be useful addition.

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