So, my car is 2006 Fabia with 1.4 75hp BKY engine, equipped with SMI Koyo PAS system. The car has 198k km in clock. The power steering assistance has been playing its game for a couple of months now and I am running out of ideas and patience. Any clues would be much appreciated, as I would like to avoid spending the price of the car to replacing the pump and steering rack.

 

Symptoms: PAS works only occasionally, usually after cold start. It works normally for about 10s to 10mins and suddenly goes into some sort of limp mode when I turn the steering wheel. In this mode pump still runs but the steering assistance is poor. There are no warning lights or fault codes (read with VCDS), which is strange. The orange steering wheel light is lit for few secs after switching IGN on, as it should.

 

PAS related problems are not rare with Fabias, but in all other cases I have read either the steering wheel symbol is permanently lit or there are fault codes in the PAS or engine ECU together with the problem. The problems are usually related to cracked PAS fuse, poor battery condition, faulty steering angle sensor or corrosion in electrical contacts. 

 

What I have done:

Checked the pump fusing: was OK

Checked the PAS fluid level: was OK

Checked and measured the alternator DFM signal wire: was OK

Renewed battery and alternator, checked belt and tensioner: system charges at 14,3-14,4 V

Cleaned and tightened the battery +/- terminals: were OK

Cleaned the grounding point of the battery ground cable: no corrosion was visible

Cleaned the connectors at the pump end as well as the grounding point of the pump ground cable: no signs of corrosion, dirt or water 

Logged PAS with VCDS: pump runs at specified speed, steering angle sensor values seem OK, and all looks normal to me except when the PAS goes to limp mode. Then the pump motor takes max. 20 amps current, no matter how I shake the wheel. When PAS works, it takes >50 amps when turning the wheel. With 20 amps max it feels like there is no PAS at all. You need both hands if you want to turn the car at low speeds. Not nice.

 

I even tried changing the coding of the PAS, and it works as it should. Eg. changing coding to handicapped mode really makes the steering light as feather, but only until the limp mode kicks in again.

 

Am I missing something here? What else could I have a look on? It would be nice to hear if someone has had similar issues, where no fault indicators are active even there is a fault situation going on. 

 

I attached a short xls file from one measurement. Comments on that?

PAS_problem.xls

Steering angle sensor?

As mentioned, no fault codes from steering angle sensor and steering angle value seems reasonable when logged with VCDS.

Ok but you don't always get fault codes from the sensor.

I suspect the pump unit is starting to fail, there really is no easy way to diagnose the problem and the pump ECU is very simple and offers few codes and often none at all.

Thanks for your tips so far, keep 'em coming 

 

The G250 steering angle sensor on SMI Koyo rack seems to have 4 pins, so I assume it contains double sensors (steering rate & direction), probably inductive ones. Due to my stingy nature, I think I will have to make some oscilloscope measurements before buying a new sensor... it does however sound a lot better than changing the pump (and rack, if done by the book).

 

BTW I just found this thread which is first found by me mentioning PAS going sporadically into limp mode. However in that thread it is said that they have had either steering wheel symbol on dash or fault codes from G250 sensor.

 

Luckily it seems that winter is coming... less grip = lighter steering?

You won't need a new rack whatever the outcome, the rack is just a hydraulically powered mechanical unit and sounds to be in perfect working order.

You either need a new sensor or a new pump, there are no other parts in the system, it's completely separate from the rest of the cars electronics.

This problem seems to be finally solved   All it needed was just a replacement PAS pump... I could not find any problem with steering angle sensor (actually turned out to be Hall-type), so it was either the pump or rack. 

 

I ordered a renewed PAS pump from a Polish company, Auto Fun. It cost abt. 220 € inc shipping to Finland and it comes with 2 yr warranty. IMO this was the most feasible solution taking into account the value of the car.

 

The reason I talked about changing both pump and rack was because I recall seeing some information that SMI Koyo parts should be renewed together for some reason (maybe €€€...?)

 

Of course I had to disassemble the old PAS pump, and actually I found some damaged sealings at the gear pump located in the unit. It sounds logical that there was an internal pressure leak between intake and outlet of the gear pump. There was also some corrosion visible inside the PAS pump, but not very much - looks like electronics are still intact.

 

I mounted the "new" pump, filled the system with fresh PAS fluid, started the engine, did a few lock-to-lock twists and checked the fluid level. Dropped the car on its wheels and went for a test ride - worked like a charm from the first moment!

 

Thanks to all or your comments and help!