Tight/Heavy steering on a 2006 Mitsubishi Colt 1.1 petrol

Question

Car is a 2006 Mitsubishi Colt 1.1 petrol.

It has electric power steering (EPS) with no hydraulic fluid involved.

When stationary or moving slowly, the power steering can be felt to be working, I can easily turn the steering wheel with the car stationary.  When driving quickly, the steering wheel becomes tight to turn and does not self centre.

I presume the power steering is meant to give proportional assistance depending on how fast the car is moving, with greater assistance at slower speed.  This makes me think that something to do with the steering is tight all the time, but the slow speed assitance is hiding it when moving slowly.

If I turn off the ignition, the steering wheel is tight to turn.  Likewise if I disconnect power to the EPS ECU, the steering is tight and the EPS warning light then comes on.  With both front wheels off the ground and the steering lock off, it is very difficult to move the steering by pushing on the road wheels.

I have disconnected the track rod end ball joints from both hubs, the hubs steer freely, so it is not faulty bearings at the top of the struts and the steering wheel still feels tight.

I have never done any work on a car with full EPS before, so am not sure what to expect under different circumstances.  I presume that there must be a fault in the steering rack, but I thought I would check with you guys to see if there is something I have missed.

I have read one account on a website where someone describes a similar situation.  He described a plastic gear inside the EPS motor that had swollen, which was causing tightness, so maybe this car has the same issue.

I have also found a website where they repair faulty EPS ECUs, but their advert sounds like the usual fault is that the steering is always heavy.  I think that the electronics are OK since it does appear to assist at slow speeds.

Does my diagnosis sound correct?

Also if you have worked a Mitsubishi Colt steering rack, what is the easiest way to remove it?

HandyHowie · Answer

I managed to fix this issue with the EPS.
I removed the steering rack from the car, which required dropping the front sub frame -

I could see that the aluminium casing was badly corroded -

Before I dismantled anything, I fastened some mole grips onto the steering input shaft to get a feel for how tight it was to turn off the car.
Some of the joints between different components appeared to be swollen due to the corrosion, for example where the steel casing of the motor mated up to the EPS body -

The bolts were difficult to remove and one of them snapped, so I had to drill it out.
I also dismantled some of the EPS body -

With the EPS disassembled, i again turned the input shaft and found it to be move more freely than before. Not finding anything obviously wrong, I cleaned all of the mating faces and reassembled the EPS.  The assembly was still easier to turn by hand.
I believe that the corrosion between some of the mating faces was causing miss alignment of the components, which was causing increased friction.  For example, the motor casing was probably slightly twisted due to the corrosion.
The car has been in use regularly for about 7 months and the steering is still working correctly.
There clearly was nothing wrong with any of the electronics.

Tight/Heavy steering on a 2006 Mitsubishi Colt 1.1 petrol

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