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Chassis guides and mods

Power Steering Fault

it is a common occurance for the Roadster power steering to become intermittent

Modification Details

Fixing Intermittent Power Steering

This is mainly a Roadster problem so I will only cover the Roadster although the 450 is similar.

Open the bonnet and remove the boot bucket from the front of the Roadster.

On the left hand side of the battery are 3 connections, 1 earth and 2 plugs.
Circled below shows the earth and the motor power connector.

On a disassembled PAS (power assisted steering) rack you can see the connections more clearly.

Circled in yellow are the 2 possible earth connections. These corrode which can affect the connection. Pull the connection off and clean with sand paper or wire wool.
A spray of contact cleaner on the tabs and connections will also help.

Reconnect the earth connection. You will only have 1 earth cable and you
may have 1 or both of the connection tabs. Whichever one you use is fine.

The final 2 main connectors should be sealed but it is always worth the time to disconnect
them and give all parts a quick spray in contact cleaner before reconnecting all
of the connectors. The top connector in the picture is the power to the power
steering motor, the lower of the 2 connectors is the column rotation sensor.

This should sort out the intermittent nature of the steering fault.

It Still Doesn't Stop The Problem

Check the cables coming away from the steering rack, you are looking for splits
in the sheathing ,chaffing and obviously cables that have been cut through totally.

Check for water under the carpet. The PAS controller is attached to the centre console,
underneath the dash, in the footwell, hidden by the carpet. Although it is unlikely,
there is a small chance that this controller could become water damaged.
While you are looking at it, ensure the connections to it are OK and pushed in tightly.

Pull fuse 35 for the power steering and replace it with a fresh one, make sure it's tight when
reinserted as a loose fuse could cause intermittence through the vibration of the engine.

The Problem Is Still There

There is a possibility of debris getting into the steering rack. Check the rubber bellows
on each end for splits and make sure the clips are holding rubber bellows in place.

If your rack has become contaminated there isn't much you can do apart from replace
it or try to take your existing one apart to clean it out, if you do attempt that, good luck.

Contact Cleaner

Also called switch cleaner. It can be bought from places such a Maplin.
If you are an online buyer then Google or Ebay search for contact or switch cleaner.

Servisol and Ambersil both do such a product and neither are expensive.

The Car Steers Itself

It's fairly rare but was captured by Steve on his 450 Fortwo.

It's most likely a fault with the rotation sensor in the steering rack but it could be a fault with the PAS controller.
We are seeing lead-free solder joint issues all over the world so it could be a cracked solder joint in the controller.

There's a possibility that a temporary fault could be occuring in one of the wires. Depending on how
the PAS controller sees the signal from the rack rotation sensor, a failing cable could create a pulsed
voltage which the PAS controller could possibly interpret as the sensor reading a rotation.


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