Hi All

Firstly - I am posting this in the "general" as I find the c max forum to be dead at the best of times...

Driving on the motorway earlier and suddenly an amber warning - steering malfunction - service required albeit steering is normal. I then cycled the ignition to try and clear the fault and straight away red warning - power steering failure - pull over (or words to that effect). No power steering the rest of the day. Back home now and plugged in For Scan and the following - U0420 invalid data from power steering control module A. I have cleared the codes and the power steering is back to normal again, took it a short drive and all is well.

I have had a quick google but didn't find it overly helpful

Any ideas or things to check to prevent future occurence

Thanks

Craig

Low battery charge is the first thing to check here.

These electric steering racks are a fairly common failure though, so I wouldn't be surprised if the rack is failing internally. You can check the wiring and plug for any signs of damp, corrosion or chafing. But that was more common on the older EHPAS models.

When this problem occurs while driving on the motorway it is almost certainly caused by the EPAS steering rack failing.

Low battery voltage causing the warning usually occurs just after a cold start. However, it is worth to check the battery voltage and condition before replacing the steering rack.


Unfortunately, failure of the EPAS steering rack is quite common. These steering racks consist of a ball nut mechanism that is driven by an electric servo motor with an integrated control module. The servo motor is connected to the ball nut mechanism by a small toothed belt.

It is usually the integrated control module that fails either due to water ingress or failed electronic components. However, the servo motor/control module is part of the steering rack and is not available as a spare part. Removal of the servo motor/control module requires the full steering rack to be disassembled since it is bolted to the rack from the inside.

Back in the days I managed to repair one of these steering racks, but the amount of labor involved was not really worth the effort. Installing a used steering rack can also be a hit or miss. On one hand a used steering rack can be incompatible with the vehicle or suffer from the exact same problem soon. On the other hand, there is the risk of buying a steering rack which has the steering angle limiters installed/activated (which cannot be undone). Steering angle limiters are only installed/activated on 18 Inch (or larger) wheels.

Therefor I recommend installing either a brand new steering rack or having the existing steering rack professionally repaired/refurbished.

I noted there was quite abit of rust on the fuse / feed to the power steering rack ( the connections in front of the battery box ). If the rack is indeed failing then I doubt I will replace as the cars simply becoming a money pit.