Slow battery drain caused by failing power steering pump?
 

Hi! I'm new to the forum and trying to get started doing my own work on my 2003 Mini Cooper with 94,000 miles.

I have been having a persistent slow battery drain that the mechanic could not diagnose. It is quite slow and will take about 7 days before I need to jump the car. The mechanic had the car for over 2 months and could not find the issue. They tried replacing the battery, disconnecting the radio, replacing the steering angle sensor (this seems so wrong), and cutting the connection to my after-market driving lights with no success. During this time the only thing I noticed was that the lock actuator for the driver's side door had failed.

Flash forward to a few days ago and I have purchased a voltmeter with the intention of trouble-shooting the issue. However, after jump starting the car and driving around to charge up the battery, I now have a persistent fan noise running under the car after the car is turned off. I believe this is the power steering fan, which drains the battery even more quickly (~1 night).

My question is this: am I dealing with two separate issues (a bad power steering pump plus a slow battery draw from perhaps the dead door actuator?) or one issue (a failing power steering pump that was slowly draining the battery). My thought is to start by replacing the power steering pump and fan and then assessing whether the slow leak is still happening. Am I going about this correctly? Any help would be much appreciated!

My first step would be to get a service manual. I’d personally troubleshoot the battery drain problem first.

Are you familiar with using a meter? If not, find someone to help! I’d trace the slow drain by removing the negative battery cable, and putting the meter leads in series between the battery and cable, with the meter set to the highest Amperage (DC current) has range. (Set the meter before putting it in the circuit!) You can go to a lower range if needed.

You should see less than 1/10th of an amp (or so) being drawn from the battery with the car completely off. I can’t remember what the amp draw is for sure, but it’s small. If it’s more, I’d pull fuses, starting with the accessories, until the amp draw drops off.

The service manual will tell you which fuse powers what so you can check the offending circuit once you know which one it is. Hope that helps.

Edit: What is the voltage across the battery with the car running?

Thanks for your reply, Dan! I will get a service manual, that's a great idea!

I am not very familiar with the meter, but I have a colleague helping me out. He suggested the same process, however I was unclear about whether the car has a "sleep" and "deep sleep" mode. I was worried the car wouldn't go into "deep sleep" with the fuses pulled, which would make it quite a bit more complex. So I was planning to figure out some way to check the current at each fuse after the car is in deep sleep (some combo of small metal pieces and alligator clamps to make a meter accessible "fuse").

The voltage across the battery with the car running is 14.0 volts, so I think the alternator is fine. Is that about correct? Thanks again!

My daughter’s car has 14.5 volts at idle. Somewhere on this board I saw a thread that said Mini’s get flaky at about 13.8 or 13.4 volts, something like that, can’t remember. I’d try revving the engine to around 2000 or 2200 rpm’s and see if that raises your voltage closer to 14.5V. It’s possible the voltage regulator is on its way out. I’m not yet sure if the regulator is in the alternator or mounted separately elsewhere.

We’ve had our Mini for less than 2 weeks, I’m still learning myself, but have worked on a lot of other makes and models so I have that knowledge to help.

I recommend the Bentley Service Manual, it covers the subject much better than the Chilton’s or Haynes books. They aren’t cheap, but you get what you pay for and good used copies are available online.

The one I bought is the later one that covers 2002 through 2006, and this book includes “Diagnosis Without Guesswork”.

There is an earlier version available that covers 2002 to 2004 (IIRC the years right)

I’d also recommend using/modifying a blown fuse to gain access to a circuit protected by a fuse. The reason for this is that you don’t want to damage the fuse clips in the fuse block by stuffing something in there that deforms them so bad they can’t grip a fuse anymore! I learned that the hard way.

Your local auto parts store would likely have an inexpensive tool for this, it’s worth a try.

Let us know what you find.

Dan

Have you confirmed where the fan noise is coming from? It’s either going to be the power steering or radiator fan. Radiator fan is unmistakeable as its loud. Does the fan noise stop at some point? If it doesn’t shut off I’d say that’s the issue. Disconnect power to the power steering and see is that stops the power drain.

I haven't confirmed where the fan noise is coming from, but it seems like the region of the power steering, and not the radiator fan. The fan noise isn't on when you first start the car, but comes on after driving a bit and then doesn't turn off. There is also heat radiating from the region of the power steering pump after driving for a bit. I just did a parasitic battery draw test and everything is normal. The car is drawing about 30 mA and didn't drop at any point when I pulled the fuses one at a time. That was starting from completely cold though.

I'm starting to think that the power steering pump fan isn't working. Then the power steering pump would begin to overheat and continue to run in an effort to cool itself? I tried pulling every fuse when the "fan noise" was happening but couldn't find a fuse that stopped it. That would point to the noise coming from the pump, right?

Thanks for your comments :)

Quick update on this post, I have fixed the issue!

With the help of a friend I confirmed that the "fan noise" was in fact the power steering pump itself. It would spontaneously turn on even when the car hadn't been driven for a while, which would quickly drain the battery.

I know power steering pump failures are common, but I thought I'd share my story of an intermittent failure in case anyone else is experiencing the same. I figured out the issue by:

1) Doing a parasitic drain test, finding the drain to be in the normal range.
2) Confirming the the power steering pump fan was working by using a borescope to look under the car with the AC running.
3) Testing that the sound was coming from the power steering pump by removing the power steering pump fan and then disconnecting the wire that should tell the pump when to turn on. I found the pump was still running, suggesting an internal failure.

Then I replaced the power steering pump. All better!