[MK2] [N/A] Power Steering Motor Not Stopping

[webb2800]

Hi All,

After getting the car back on the road after a few years my P/S motor seems to be much noiser than I remember. It's practically silent when the car first starts but after a little driving you can hear it from inside the cabin.

This has also come with another odd bug. Per other info I've read on the P/S system, the pump should autmotically switch off if the wheel isn't moved for a while (and the car is under about 10mph) mine currently runs constantly. I've got not warning lights and I've followed the diagnostic in the BGB and confirmed the steering postion sensor works as intended. I've also flushed and replaced the fluid. I wondered if the P/S ECU was faulty but that apparently usually results in no P/S at all and/or a warning light. I'm pretty sure the motor is switching off as intended at high speed but it could be noise from the engine masking the sound.

Any ideas on what else could be preventing the motor from switching off at idle?

[ChrisW]

There's a "power steering driver" next to the power steering ECU. I don't know much about it but looks like it controls the P/S motor using signals from the P/S ECU. I suppose that could be faulty but I don't know if there's any diagnostic tests you can do on it.

The relay is known to get stuck "off" rather than "on". If it was stuck "on" then presumably your P/S motor would keep running even with the ignition off, so it can't be that.

Seems likely it's either a broken wire or a faulty P/S ECU or "driver". Sorry I can't be more specific, I haven't got any experience diagnosing this system.

[jimi]

This has also come with another odd bug. Per other info I've read on the P/S system, the pump should autmotically switch off if the wheel isn't moved for a while (and the car is under about 10mph) mine currently runs constantly. I've got not warning lights and I've followed the diagnostic in the BGB and confirmed the steering postion sensor works as intended. I've also flushed and replaced the fluid. I wondered if the P/S ECU was faulty but that apparently usually results in no P/S at all and/or a warning light. I'm pretty sure the motor is switching off as intended at high speed but it could be noise from the engine masking the sound.

Any ideas on what else could be preventing the motor from switching off at idle?

Where did you find/read this information ?
Because none of the information ( BGB's, Wiring diagrams) that I have mention anything about the pump switching off at idle.

EHPS (ELECTRO HYDRAULIC POWER STEERING)
SYSTEM OUTLINE
THE EHPS (ELECTRO HYDRAULIC POWER STEERING) SYSTEM FUNCTIONS TO CHANGE THE FORCE REQUIRED FOR STEERING MANEUVERS, AND THEREBY PROVIDE THE IDEAL STEERING FEELING FOR AT VEHICLE SPEEDS AND STEERING CONDITIONS. THIS IS DONE BY THE POWER STEERING ECU CONTROLLING THE HYDRAULIC PRESSURE ACTING UPON THE HYDRAULIC REACTION CHAMBER (LOCATED IN THE GEAR BOX CONTROL UNIT) BY REGULATING THE POWER STEERING MOTOR’S SPEED (AND HENCE THE AMOUNT OF FLUID FLOW).
EHPS OPERATION
WHEN THE IGNITION SWITCHED ON, STARTING CURRENT FLOWS FROM THE GAUGE FUSE TO TERMINAL IGB OF THE POWER STEERING ELECTRONIC CONTROL UNIT, TERMINAL VS OF THE STEERING POSITION SENSOR, AND TERMINAL (A) 4 OF THE POWER STEERING DRIVER.
THE VEHICLE SPEED IS DETECTED AT THE SPEED SENSOR, AND SIGNALS ARE INPUT AS CONTROL SIGNALS TO TERMINAL SPD OF THE POWER STEERING ELECTRONIC CONTROL UNIT AND TO TERMINALS SS1 AND SS2 OF THE POWER STEERING ELECTRONIC CONTROL UNIT.
WHEN THE ENGINE IS STARTED, SIGNALS ARE INPUT TO TERMINAL EFI OF THE POWER STEERING ELECTRONIC CONTROL UNIT FROM THE ENGINE OF TERMINAL PSCT OF THE ENGINE AND ECT ECU. AS A RESULT, THE CURRENT APPLIED TO TERMINAL IGB OF THE POWER STEERING ECU FROM THE GAUGE FUSE FLOWS FROM TERMINAL MRLY OF THE POWER STEERING ECU → TERMINAL (B) 1 OF THE POWER STEERING RELAY → TERMINAL (B) 2 → GROUND, AND THE POWER STEERING RELAY IS SWITCHED ON. AS A RESULT, THE CURRENT APPLIED TO TERMINAL (A) 1 OF THE POWER STEERING RELAY FROM THE ABS FUSE FLOWS FROM TERMINAL (A) 2 OF THE POWER STEERING RELAY → TERMINAL (B) 1 OF THE POWER STEERING DRIVER AND TO TERMINAL (A) 1 OF THE POWER STEERING MOTOR.
IF THE VEHICLE SPEED IS LOW, THE SPEED OF THE POWER STEERING MOTOR IS INCREASED BY INCREASING THE VOLTAGE OF THE CURRENT THAT FLOWS FROM TERMINAL (A) 1 OF THE POWER STEERING MOTOR TO TERMINAL (A) 2 OF THE POWER STEERING MOTOR → TERMINAL (B) 2 OF THE POWER STEERING DRIVER → TERMINAL (C) 2 → GROUND, WITH THE RESULT THAT THE VOLUME OF FLOW OF THE POWER STEERING FLUID BECOMES GREATER, THUS PROVIDING A LIGHT STEERING FEELING.
WHEN THE VEHICLE SPEED IS HIGH, THE SPEED OF THE POWER STEERING MOTOR DECREASES AS A RESULT OF THE REDUCED VOLTAGE APPLIED TO THE POWER STEERING MOTOR, AND THUS THE VOLUME OF FLOW OF THE POWER STEERING FLUID IS REDUCED, SO THE STEERING FEELING IS MORE RESISTANT.

If there's no PS warning lights and the diagnostic procedure doesn't show any faults then it would suggest to me that the system is OK.
Noisy pump could be down to worn brushes/bearings, air in the system/aeriation of fluid, low oil level.
Jimi

[webb2800]

Tbh, I've never seen any official documentation suggesting that the motor switches off at idle but it's something I've seen mentioned on many forums/topics. Some more googling suggests that the motor doesn't switch off but just slows down until turning input is detected. Again - can't seem to find any official confirmation of this behaviour other than the steering sensor diagnostic in the bgb having two tests: one at 0mph and a rolling one. If the motor just slows down that would explain why I always hear the noise - especially if the motor is on the way out and noiser than usual.

As for the motor, I've already tried re-surfacing the brushes. Is the motor itself serviceable, or is the only option to replace it?

[SonicSW20]

Where did you find/read this information ?
Because none of the information ( BGB's, Wiring diagrams) that I have mention anything about the pump switching off at idle.

Pump on mine turns off if the wheel is not touched for a short period of time. Every SW20 I've had with PS has done this.

[jimi]

Pump on mine turns off if the wheel is not touched for a short period of time. Every SW20 I've had with PS has done this.

Thanks for confirming, I thought I'd heard that before but couldn't find anything about it in the BGB's

[webb2800]

Where did you find/read this information ?
Because none of the information ( BGB's, Wiring diagrams) that I have mention anything about the pump switching off at idle.

Pump on mine turns off if the wheel is not touched for a short period of time. Every SW20 I've had with PS has done this.

Roughly how long does it take before it switches off?

Any ideas what could cause the system to not do this?

[Juliuswws]

Hi, it supposed to shut off after 20 seconds if you are stopped and the don't move the steering wheel.

I would check and replace all capacitors in the PS ECU and driver board. They tend to cause problems at their age.
I made a quick guide years ago:
https://www.imoc.co.uk/viewtopic.php?p=&t=194300

Cheers