hi guys, so I have a problem with my 2003 mini cooper. My check engine, abs and brake light all came on at the same time. P0500 code after testing it with a scanner. Replaced both of the rear wheel speed sensors today. Didn't help, but ran into a problem. My speedo works but when I turn my headlights on, my speedometer stops working. The needle drops down to 0 mph. If I start the car with my headlights on the speedometer will work. It only stops working is when my driving and turn my headlights on. Any suggestions ?

I replaced the sensors with after market ones. It was cheaper and I'm on a budget.

 

Did you check the Battery/Alternator?

 

I replaced the alt. Last year. As far as the battery goes no I haven't checked it. I never had this issue before replacing the rear wheel speed sensors so why would the battery now be an issue.

 

Because when you turn your lights on, things stop working

 

Just because you replace the alternator doesn't mean it's still working, especially if it's a discount parts house brand unit (Autozone, O'Rilleys/Kragen, Napa).

Get a volt meter put it on the battery while someone turns on the lights, if the voltage drops below 13 volts your alt is not doing it's job.

 

Actually, with the car running, the voltage shouid be no lower than 14.0 volts, as the system on these cars needs that to function properly. (14.2 to 14.5 is proper spec) If the battery is worn out, or the alternator is not charging enough, you will have many codes, that will come and go and many weird things with the electrical can occur.

 

I was told because I'm having this problem now after I replaced the 2 rear speed sensors, they could be the problem.

 

 

Tested the battery. 12.5 with the key in the on position. Had my buddy start the car while I had both Leeds on the terminals. Dropped down to 10.8 then going up to 13.96 and stood there.

 

 

The battery is factory still. Still has all the bmw stickers on it. Maybe the previous owner replaced it with one from mini..? Who knows, I never replaced it. I've owned the car for 3 years .

 

Hmm, well, 15+ years is a loooong time. MINI = BMW, but who knows, if you're not the original owner, all bets are off on the fidelity of that battery.

BTW, I've had fairly good luck with First Interstate batteries. They also have a refurb program where you can buy refurbished batteries very inexpensively. I think the last time I checked, a battery for a MINI was about $180 new and $50 for a refurb.

 

That's for the information. Tomorrow I'll most likely take it down to a local autozone and they'll test it for me. Unless there's a test I can do at home??

 

Kyle

There's a date on BMW/MINI batteries. Check that first to see how old your battery really is.

I replaced my original 2002 battery in 2013 for $155.99 after 11 years.
Autozone have batteries that are perfect replacements for MINI batteries.

If the battery isn't the problem, I'd disconnect the new sensors at their plugs, ignore the warning light & see if everything else then works correctly.
I'd also check all the ground cables & battery connections - they should all be clean & bright & tight. The critical one is under the right side engine mount, clearly visible (at least on the 'S'), but there are several others.

 

I honestly don't see how grounds could be an issue now. I never had this problem before replacing the wheel speed sensors.

 

You may well be right! It's just that the grounds are very sensitive on Minis & everybody else went straight for a battery problem.

I'd disconnect the new sensors at their plugs, one at a time if you like, ignore the warning light & see if anything changes.

PS - I'm trying to save you $160!!!!

 

Disconnected the sensors at the plugs. Nothing changed. When for aa drive. Speedo works but as I'm driving and turn on the headlights, the needle drops and starts to shake a little. Weird

 

Did you suggest I drive the car with both sensors I replaced unplugged? And see what happens. I'm sorry I completely overlooked that part of your ocmment.

 

Yes, Kyle, & it looks as though you've done that.
If the speedo & lights problem still exists, then it's co-incidental with changing the sensors.

My motto is always "Do the cheap stuff first"!
So now I'd check & clean the battery connections & grounds, then check the plugs for corrosion on the modules that control the headlights & speedo. All this is just your time = 'free'!

You could try disconnecting the battery overnight.
If all those check out, then look at the battery & consider replacing it. How old is it?

 

I didn't drive the car with the sensors unplugged. Sorry I should of been more clear about it. I just unplugged them both and plugged them back in to make sure they where good I guess..I'm not sure how old the battery is tbh. It still have the bmw stickers on it.

 

This was the code for the check engine light.

 

Did Autozone load test the battery? What was the result?

 

Ah-ha! That's really key to diagnosing (at long distance) whether it's a sensor issue or a battery/ground issue. If the speedo works correctly with one or both sensors un-plugged, then you know it's a sensor issue.

Did AutoZone clear the P500 codes?
I don't think they need to, but you do need to drive the car for a few minutes after replacing sensors.
Apparently some inexpensive sensors just flat out don't work, even if they are listed for a Mini. AZ list a dozen or so from $30-$120 & I don't know what the difference might be. There are several other threads on this forum.

The battery date is in clear sight on the top of the battery.

 

Tomorrow I'll get the date on the battery. No tests were done to the battery due to me being in a rush and having some other things to do so I'll go back tomorrow also. These sensors were also really cheap. I did not buy them from mini. Also tomorrow I will unplug them again and drive around and see what happens. Thank you guys so much for helping me with this.

 

Unplugged sensors and went for a ride, the speedo didn't work at all. Then I plugged just the driver rear in. Drove around. Speedo worked. Dropped again when I turn my headlights on. I then plugged in the passenger rear. Same out come. Check the date on the battery and I literally couldn't find one anywhere. I noticed a sticker on the side from 2016 . I had brought it to get charged at autozone cas it had died after my alt. Had failed on me. Noticed the negative terminal was a bit lose. Tightened it, went for a drive. Turned on headlights while driving and it barely dropped. It wasn't as bad. It dropped maybe 200 rpm only. Before it was drop down to 0 mph. Check engine still on for wheel speed sensor