R50/53 Power steering pump runs with key on?
1st Gear
Joined: Dec 2022
Posts: 29
Likes: 5
Relevant to this thread: I recently replaced a failed alternator (rear bearing gone bad) in my '05 MCS.
With the alternator removed, the PS pump runs when the key is in the ignition position (i.e. all electrical accessory operational, but engine off).
With the new alternator installed, the PS pump runs only when the engine runs.
So the PS pump can be fooled into believing the engine is on if there's a problem with the voltage regulator in the alternator.
With the alternator removed, the PS pump runs when the key is in the ignition position (i.e. all electrical accessory operational, but engine off).
With the new alternator installed, the PS pump runs only when the engine runs.
So the PS pump can be fooled into believing the engine is on if there's a problem with the voltage regulator in the alternator.
Really wouldn't have expected to see the behaviour I'm getting with the alternator removed/disconnected
I've just removed my pump again, it's going off for repair, it sounds awful anyway so needs looking at
If I continue to see the same behaviour when refitted then will definitely look at changing the alternator
1st Gear
Joined: Dec 2022
Posts: 29
Likes: 5
Hi, bit delayed but thought I better come and close this one off
In my case, a refurbished PS pump fixed the issue.
Lesson learned, don't buy a pump from a breaker car, it's likely to be faulty or fail soon
Refurb pump has 2 year warranty, so it's piece of mind
Thanks all for the advice!
In my case, a refurbished PS pump fixed the issue.
Lesson learned, don't buy a pump from a breaker car, it's likely to be faulty or fail soon
Refurb pump has 2 year warranty, so it's piece of mind
Thanks all for the advice!
Neutral
Joined: Mar 2021
Posts: 4
Likes: 2
100% the answer to the original question.
So much misinformation from various other powersteering behaviours and symptoms. Let me clarify..
1) if your pump stays on after the key is off this is a different issue involving carbon buildup and faulty power steering pump.
2) if your pump is coming on and slowly spinning up in the acc key position without the engine on this is a wiring or alternator issue not a pump issue.
3)if your pump only comes on when steering with the engine on it is operating correctly.
The original question is specifically describing the symptoms of 2) so the wiring needs to be checked and made sure its connected correctly to the alternator and ground and if that's all OK the alternator and ONLY the alternator is at fault. Perhaps an adtermarket replacement or a cheap ebay job that dosent have the correct module for the power steering.
1) if your pump stays on after the key is off this is a different issue involving carbon buildup and faulty power steering pump.
2) if your pump is coming on and slowly spinning up in the acc key position without the engine on this is a wiring or alternator issue not a pump issue.
3)if your pump only comes on when steering with the engine on it is operating correctly.
The original question is specifically describing the symptoms of 2) so the wiring needs to be checked and made sure its connected correctly to the alternator and ground and if that's all OK the alternator and ONLY the alternator is at fault. Perhaps an adtermarket replacement or a cheap ebay job that dosent have the correct module for the power steering.
Last edited by Pete Doughty; Apr 24, 2025 at 10:18 PM. Reason: Comes off as rude but edited to be more
Neutral
Joined: May 2025
Posts: 3
Likes: 2
From: Paris
What if yellow wire voltage is always 0 or near 0?
Thought it was worth an update...
With the key in the on position, but engine not running:
Pin 1 Green 12v
Pin 2 Yellow 0.6v
Pin 3 Violet 10v
Engine running:
Pin 1 Green 13v
Pin 2 Yellow 13v
Pin 3 Violet 13v
Long story short, with my limited knowledge I think the fault is in the pump rather than alternator or wiring
With the key in the on position, but engine not running:
Pin 1 Green 12v
Pin 2 Yellow 0.6v
Pin 3 Violet 10v
Engine running:
Pin 1 Green 13v
Pin 2 Yellow 13v
Pin 3 Violet 13v
Long story short, with my limited knowledge I think the fault is in the pump rather than alternator or wiring
Facts :
- PS pump never turns on.
- With the test tools, the pump is running ok during the 10/15 seconds of the test.
- Tried with another ECU, same.
- Tried with another pump, same.
- New fuses, including 100A, and relay.
Voltage checked :
yellow refers to the jan 30, 2024 MiniMonkey08 post, quoting deepgrey’s manual.
Pin 2 Yellow 0v
Engine running:
Pin 2 Yellow 13v
Car design, as far as I understand but I may be wrong:
- The pump has its own control unit.
- There is a kind of logical test inside of it :
do I receive a ‘I am alive’ signal from the generator ?
If no, it means the generator is not running ok, which basically means the engine plus the car accessories run on the battery only, which won’t last forever.
Consequently, the lower the power consumption, the higher the mileage until the engine stops running.
So, as a security measure, when the pump control unit detects the generator is not running, it does not turn on the electrical PS pump.
How is this ‘I am alive’ signal conveyed ? Through a 12 V voltage at yellow cable.
No voltage or close to nothing means : the generator is not working, so pump won’t turn on because it would dry the battery.
Is there a fault code ?
The tricky thing is that the ‘alive’ signal does not provide from the generator itself.
As shown on the forementioned electrical diagram, there is a yellow/black wire connection from the generator to the instrument cluster.
The yellow wire does not start from the generator itself, it is plugged onto the black/yellow wire.
So, in case there is some trouble with the yellow wire only and if the generator is running ok, the black/yellow wire provides the cluster with the ‘alive’ signal (consequently no fault code and no red light on the dash) whereas the yellow wire provides the pump with the ‘not alive’ signal, which does not trigger any specific fault code.
So, now I suspect the yellow wire and only the yellow wire to be at fault. Not sure this is the correct diagnosis but I have no idea how to proceed regarding this yellow wire.
Neutral
Joined: May 2025
Posts: 3
Likes: 2
From: Paris
Experiencing an issue connected to these posts and still unsorted.
Facts :
- PS pump never turns on.
- With the test tools, the pump is running ok during the 10/15 seconds of the test.
- Tried with another ECU, same.
- Tried with another pump, same.
- New fuses, including 100A, and relay.
Voltage checked :
yellow refers to the jan 30, 2024 MiniMonkey08 post, quoting deepgrey’s manual.
Yellow wire :
position I : nothing
with the engine running : nothing
Design, as far as I understand but I may be wrong.
- The pump has its own control unit.
- There is a kind of logical test inside of it :
do I receive a ‘I am alive’ signal from the generator ?
If no, it means the generator is not running ok, which basically means the engine plus the car accessories run on the battery only, which won’t last forever.
Consequently, the lower the power consumption, the higher the mileage until the engine stops running.
So, as a security measure, when the pump control unit detects the generator is not running, it does not turn on the electrical PS pump.
How is this ‘I am alive’ signal conveyed ? Through 12 V at yellow cable.
No voltage or close to nothing means : the generator is not working, so pump would not turn on because it would drain the battery.
That's for theory.
In practice, the yellow wire does not stem from the generator itself, but from a spinoff from the yellow/black wire.
This could lead to a situation where:
There is power on the black yellow wire, so at the cluster instrument level, everything is fine: no fault code of any kind, which makes things difficult to diagnose.
There is no power on yellow wire due to some malfunction on this wire. So the PS pump does not turn on, falsely believing the generator is out of order.
I bélieve this explains why the PS pump does not run on my car.
I can add two things:
- I've just replaced the generator for a cheap probably redone generator. It could be a faulty generator, but in this case, there would be a fault code. There is absolutely no fault code and two test tools were used. Besides, as I mentioned, the test tools allows the pump to run as a test.
- I thought the angle sensor could be faulty as well. An experienced mechanics told me there is no way a faulty angle sensor could impact the way the PS pump runs.
I am looking for some way to bypass the dubious yellow wire. Work in progress, any suggestion welcome. Thanks.
Facts :
- PS pump never turns on.
- With the test tools, the pump is running ok during the 10/15 seconds of the test.
- Tried with another ECU, same.
- Tried with another pump, same.
- New fuses, including 100A, and relay.
Voltage checked :
yellow refers to the jan 30, 2024 MiniMonkey08 post, quoting deepgrey’s manual.
Yellow wire :
position I : nothing
with the engine running : nothing
Design, as far as I understand but I may be wrong.
- The pump has its own control unit.
- There is a kind of logical test inside of it :
do I receive a ‘I am alive’ signal from the generator ?
If no, it means the generator is not running ok, which basically means the engine plus the car accessories run on the battery only, which won’t last forever.
Consequently, the lower the power consumption, the higher the mileage until the engine stops running.
So, as a security measure, when the pump control unit detects the generator is not running, it does not turn on the electrical PS pump.
How is this ‘I am alive’ signal conveyed ? Through 12 V at yellow cable.
No voltage or close to nothing means : the generator is not working, so pump would not turn on because it would drain the battery.
That's for theory.
In practice, the yellow wire does not stem from the generator itself, but from a spinoff from the yellow/black wire.
This could lead to a situation where:
There is power on the black yellow wire, so at the cluster instrument level, everything is fine: no fault code of any kind, which makes things difficult to diagnose.
There is no power on yellow wire due to some malfunction on this wire. So the PS pump does not turn on, falsely believing the generator is out of order.
I bélieve this explains why the PS pump does not run on my car.
I can add two things:
- I've just replaced the generator for a cheap probably redone generator. It could be a faulty generator, but in this case, there would be a fault code. There is absolutely no fault code and two test tools were used. Besides, as I mentioned, the test tools allows the pump to run as a test.
- I thought the angle sensor could be faulty as well. An experienced mechanics told me there is no way a faulty angle sensor could impact the way the PS pump runs.
I am looking for some way to bypass the dubious yellow wire. Work in progress, any suggestion welcome. Thanks.
Neutral
Joined: May 2025
Posts: 3
Likes: 2
From: Paris
solved issue ... wasn't easy to find out
Short version: the Deepgrey post below is an excellent contribution to understand how the electric power steering runs, but a key information is missing: the yellow wire should deliver in the area of 14V, if it delivers something in the area of half 14V, let's say 7V, that would not be enough.
Extended version
1/ Alternator replaced.
2/ No light on dashboard concerning the battery loading.
3/ OBD allows to test the electric power steering at 100% and 50% , both tests are OK.
4/ OBD tells Electric Power Steering is OK.
But ...
When starting the engine, no power steering.
Asked a Mini guru with tens of Mini in his backyard: found no explanation
Asked an official Mini dealer, $230/hour labour cost: found no explanation
Reminder
Electric Pump Control Unit has a 3 pin cable connector (see below).
GN/WS (green/white)
GE (yellow)
VI/WS (violet/white)
Explanation of the 1 to 4 symptoms:
3/ The test is conducted through violet/white wire (color VI/WS within Bentley illustration page 311). This wire links X6975 (at pump) to X9397, which offers the way to proceed with the OBD test.
What is this test for? This test assesses whether the pump will work when the VI/WS violet/white provides with the right voltage. It's kind of 'would the pump run on a bench?' test. The test is agnostic to the condition of the yellow or the green/white cables. BUT, in the real world, the pump relies on these yellow and green/white cables, not on the violet/white one.
4/ OBD tells Electric Power Steering is OK.
Presumably the OBD uses the violet/white cable. Same as 3/ No reason to draw any conclusion about the condition of the yellow or green/white cables.
2/ No light on dashboard concerning the battery loading.
Analysis : there would be a light in case the yellow/black cable from the generator would bring no power or not enough power.
No light means the generator is working ok.
But at position X6806 (on top of the engine head), a yellow cable is plugged on the yellow/black cable and is connected to the Steering Control Unit.
Diagnosing the cables:
Let's suppose the yellow cable is cut, there is no way to know it. We would have 2/, 3/ and 4/, no error message, but no power steering since it is the yellow cable that brings the signaling message to the pump control unit : "the generator is working ok, let's work'.
I first thought the yellow wire was the culprit.
A continuity test showed the cable in itself was ok.
Then, another test was conducted: which voltage?
yellow: a bit more than 7V.
green/white: a bit more than 14V.
Now we come the 1/ Alternator replaced.
Reminder, the yellow cable is connected to the yellow/black cable which itself comes from the generator and more precisely from the generator regulator.
The regulator has two diodes.
In case a diode is dead, the voltage from the regulator falls by half ... 7V instead of 14V.
And 7V is exactly what we have on the yellow cable.
I think the final explanation is : one of the diodes of the generator's regulator is dead.
There is enough power to load the battery, enough power to avoid a light or an obd failure, but for some reason, the pump control unit considers what it receives from the yellow cable as not enough power: so it won't ask power to start the pump engine.
Summary: the pump control unit requires to receive a certain voltage, and a not-so-faulty generator with only one dead diode out of two does not provide enough power.
Glad to share this result with you guys. The car had been sitting for months before to find out what was going on. I printed every post and every one did help to get some understanding of how this power steering works, so thanks to all of you.
Extended version
1/ Alternator replaced.
2/ No light on dashboard concerning the battery loading.
3/ OBD allows to test the electric power steering at 100% and 50% , both tests are OK.
4/ OBD tells Electric Power Steering is OK.
But ...
When starting the engine, no power steering.
Asked a Mini guru with tens of Mini in his backyard: found no explanation
Asked an official Mini dealer, $230/hour labour cost: found no explanation
Reminder
Electric Pump Control Unit has a 3 pin cable connector (see below).
GN/WS (green/white)
GE (yellow)
VI/WS (violet/white)
Explanation of the 1 to 4 symptoms:
3/ The test is conducted through violet/white wire (color VI/WS within Bentley illustration page 311). This wire links X6975 (at pump) to X9397, which offers the way to proceed with the OBD test.
What is this test for? This test assesses whether the pump will work when the VI/WS violet/white provides with the right voltage. It's kind of 'would the pump run on a bench?' test. The test is agnostic to the condition of the yellow or the green/white cables. BUT, in the real world, the pump relies on these yellow and green/white cables, not on the violet/white one.
4/ OBD tells Electric Power Steering is OK.
Presumably the OBD uses the violet/white cable. Same as 3/ No reason to draw any conclusion about the condition of the yellow or green/white cables.
2/ No light on dashboard concerning the battery loading.
Analysis : there would be a light in case the yellow/black cable from the generator would bring no power or not enough power.
No light means the generator is working ok.
But at position X6806 (on top of the engine head), a yellow cable is plugged on the yellow/black cable and is connected to the Steering Control Unit.
Diagnosing the cables:
Let's suppose the yellow cable is cut, there is no way to know it. We would have 2/, 3/ and 4/, no error message, but no power steering since it is the yellow cable that brings the signaling message to the pump control unit : "the generator is working ok, let's work'.
I first thought the yellow wire was the culprit.
A continuity test showed the cable in itself was ok.
Then, another test was conducted: which voltage?
yellow: a bit more than 7V.
green/white: a bit more than 14V.
Now we come the 1/ Alternator replaced.
Reminder, the yellow cable is connected to the yellow/black cable which itself comes from the generator and more precisely from the generator regulator.
The regulator has two diodes.
In case a diode is dead, the voltage from the regulator falls by half ... 7V instead of 14V.
And 7V is exactly what we have on the yellow cable.
I think the final explanation is : one of the diodes of the generator's regulator is dead.
There is enough power to load the battery, enough power to avoid a light or an obd failure, but for some reason, the pump control unit considers what it receives from the yellow cable as not enough power: so it won't ask power to start the pump engine.
Summary: the pump control unit requires to receive a certain voltage, and a not-so-faulty generator with only one dead diode out of two does not provide enough power.
Glad to share this result with you guys. The car had been sitting for months before to find out what was going on. I printed every post and every one did help to get some understanding of how this power steering works, so thanks to all of you.
Looks like it's the diagnostic bus.
From the manual:
"A small electric fan is used to cool off the EHPS. It is mounted on rubber bushing to the subframe to prevent vibrations from transmitting to the chassis. There is no connection nor communication between the EHPS and the cooling fan. The EHPS cooling fan power is supplied from a relay that is activated by the "same" wire that supplies power to the engine cooling fan. When the EMS2000 activates the engine cooling fan, the EHPS also gets power up."
"There are two modes of operation for the EHPS: no steering assistance and steering assistance. With the engine running and no steering assistance required the pump operates at approximately 80% capacity at a speed of 3,500 rpm. Movement of the steering changes the hydraulic pressure within the circuit which in turn affects the operation of the pump, this is identified at the control electronics by the increase in current, the pump speed is increased to 4,500 rpm and now operates at full (100%) capacity. The unit's DC motor, is capable of drawing a maximum current of 120 Amperes, but running at an average 11.5 Amperes, powers the system. In standby mode with the engine running but the vehicle stationary the draw is 7.0 Amperes ±10%."
"The EHPS consists of two connections:
2-pin cable connection
From the manual:
"A small electric fan is used to cool off the EHPS. It is mounted on rubber bushing to the subframe to prevent vibrations from transmitting to the chassis. There is no connection nor communication between the EHPS and the cooling fan. The EHPS cooling fan power is supplied from a relay that is activated by the "same" wire that supplies power to the engine cooling fan. When the EMS2000 activates the engine cooling fan, the EHPS also gets power up."
"There are two modes of operation for the EHPS: no steering assistance and steering assistance. With the engine running and no steering assistance required the pump operates at approximately 80% capacity at a speed of 3,500 rpm. Movement of the steering changes the hydraulic pressure within the circuit which in turn affects the operation of the pump, this is identified at the control electronics by the increase in current, the pump speed is increased to 4,500 rpm and now operates at full (100%) capacity. The unit's DC motor, is capable of drawing a maximum current of 120 Amperes, but running at an average 11.5 Amperes, powers the system. In standby mode with the engine running but the vehicle stationary the draw is 7.0 Amperes ±10%."
"The EHPS consists of two connections:
2-pin cable connection
- KL30
- KL31
- KL15
- KL61 (used to determine if the engine is running)
- Diagnosis bus (used for communication with the control electronics integrated in the pump)
4th Gear
Joined: Jul 2024
Posts: 333
Likes: 306
Great find!
About a month ago I also went into the powersteering pump electrical system rabbit hole. In my case the yellow wire had been rubbed through and instead of fixing that someone had decided to run a new wire to the pump from the fuseboard.
About a month ago I also went into the powersteering pump electrical system rabbit hole. In my case the yellow wire had been rubbed through and instead of fixing that someone had decided to run a new wire to the pump from the fuseboard.
6th Gear
Joined: Feb 2018
Posts: 1,734
Likes: 329
some good information in this thread, thank you @olivierparklane and others for the details
the timing of this thread / post could not be more convenient
today (and over the last few days) I've been dealing with what I thought was a bad battery. the battery light came on and the power steering was not working with the engine running. I gave it a few revs and the bat light went out (on the cluster) and power steering was back
pretty sure the alternator is going
the timing of this thread / post could not be more convenient
today (and over the last few days) I've been dealing with what I thought was a bad battery. the battery light came on and the power steering was not working with the engine running. I gave it a few revs and the bat light went out (on the cluster) and power steering was back
pretty sure the alternator is going
6th Gear
Joined: Feb 2018
Posts: 1,734
Likes: 329
thinking this one: https://www.ecstuning.com/b-tyc-part...317515030~tyc/
or this one: https://www.ecstuning.com/b-lucas-pa...2317515030kt1/
any recommendations?
or this one: https://www.ecstuning.com/b-lucas-pa...2317515030kt1/
any recommendations?
4th Gear
Joined: Jul 2024
Posts: 333
Likes: 306
thinking this one: https://www.ecstuning.com/b-tyc-part...317515030~tyc/
or this one: https://www.ecstuning.com/b-lucas-pa...2317515030kt1/
any recommendations?
or this one: https://www.ecstuning.com/b-lucas-pa...2317515030kt1/
any recommendations?
6th Gear
Joined: Feb 2018
Posts: 1,734
Likes: 329
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