Car "resets" at idle - The Unofficial BMW M5 Messageboard (m5board.com)

mamsterla · 7th December 2005, 09:56

Twice in the last week, my car has done the same thing - I can only describe it as a "reboot". I will be idling either at a stop or parallel parking. Usually there is a full electrical load - lights, stereo, etc. on.

All of a sudden the engine drops - almost shuts off. The panel lights reset, the nav turns off and back on. It is almost like I turned the key off then on quickly.

So, would people think this might be a bad battery? alternator? I think it may have the original battery and it is a 2000 MY.

Any thoughts appreciated.

VancouverM · 7th December 2005, 10:14

I had what sounds like almost the identical problem on my 99 540.
After lots and lots (and lots) of diagnostic work and road testing by the dealer, I believe the problem has finally been cured by replacing a fuel pump relay.

During road testing the shop foreman had the car hooked up to monitoring and diagnostic equipment and confirmed during an "event" there was no fuel in the fuel line. The fuel pump was replaced, but the problem recurred. The entire circuit was checked, rechecked and connections cleaned and resecured. The problem recurred. The relay was replaced and the problem hasn't resurfaced. The old fuel pump was put back in and there still hasn't been any "relapses".
He did all the testing while driving my car home every day and on the week-ends (with my approval) for two weeks.

Let us know how it goes. Good luck!

verhagke · 7th December 2005, 15:07

My vote is the battery. When engine is idling, your alternator is probably not providing any current as they kick in around 1200 rpms. When batteries go, it's not uncommon for them to act intermittently.

jclyman · 7th December 2005, 16:06

Another thought, although it sounds like a fuel pump relay may be the culprit. I worked for a BMW dealer in the '90s. We had a customer's 5 series that would mysterously stall. It happened multiple times before we found a solution. The fuel pump relay ... and, the car was almost brand new.

But, my suggestion, and it happened on my 320i, was a bad ignition switch. It would work fine almost all the time, but once in a while it would allow the engine to die. Difficult to diagnose.

Good luck, I know these cars can be difficult to diagnose ...

gsfent · 7th December 2005, 16:50

Quote:

Originally Posted by jclyman

Another thought, although it sounds like a fuel pump relay may be the culprit. I worked for a BMW dealer in the '90s. We had a customer's 5 series that would mysterously stall. It happened multiple times before we found a solution. The fuel pump relay ... and, the car was almost brand new.

But, my suggestion, and it happened on my 320i, was a bad ignition switch. It would work fine almost all the time, but once in a while it would allow the engine to die. Difficult to diagnose.

Good luck, I know these cars can be difficult to diagnose ...

Good advice on possible ignition switch, although it would be more suspect on older cars. I would think battery could be tested, say at Sears, for free. That would rule that out or confirm as the culprit. And if fuel pump relay is not too much $$ and is accessible, another easy try.
Regards,
Jerry

emccallum · 7th December 2005, 16:57

Back in 1983 my father bought a new 533, the first our family ever owned, with 23 miles on the car it had to be towed to the dealer....After the Jersey HP stopped us for towing the new BMW behind a cadillac heading to the dealer on New years eve. I think after the HP saw the SC plates he just shook his head and called for the flatbed. Ended up being a bad fuel pump relay. Bosch relays have been going bad for a long time!!

ernest

Quote:

Originally Posted by jclyman

Another thought, although it sounds like a fuel pump relay may be the culprit. I worked for a BMW dealer in the '90s. We had a customer's 5 series that would mysterously stall. It happened multiple times before we found a solution. The fuel pump relay ... and, the car was almost brand new.

But, my suggestion, and it happened on my 320i, was a bad ignition switch. It would work fine almost all the time, but once in a while it would allow the engine to die. Difficult to diagnose.

Good luck, I know these cars can be difficult to diagnose ...

VancouverM · 7th December 2005, 18:10

Quote:

Originally Posted by jclyman

Another thought, although it sounds like a fuel pump relay may be the culprit. I worked for a BMW dealer in the '90s. We had a customer's 5 series that would mysterously stall. It happened multiple times before we found a solution. The fuel pump relay ... and, the car was almost brand new.

But, my suggestion, and it happened on my 320i, was a bad ignition switch. It would work fine almost all the time, but once in a while it would allow the engine to die. Difficult to diagnose.

Good luck, I know these cars can be difficult to diagnose ...

The ignition switch was actually one of the items that they replaced in their quest for the cure.

hudson · 8th December 2005, 00:34

A fuel pump relay would NOT make the nav system reboot it would stall the car but not take power away from the lights, nav, panel lights, etc. You need to look for a problem with the battery or a main connection to the battery. The high power battery sources should be in the trunk on the right side behind the drop down panel. Check to make sure all connections are tight there and at the battery.

Joe

VancouverM · 8th December 2005, 00:56

Quote:

A fuel pump relay would NOT make the nav system reboot it would stall the car but not take power away from the lights, nav, panel lights, etc.

I'm not certain that's correct. My electrical system would momentarily shut down (reboot as mamsterla described it) this was confirmed by the shop foreman during his diagnostic and testing work. As the engine stalls out because of fuel starvation, there is a drop in voltage and a lag before it's picked up again by the battery. Every light in my car would light up right after it died.

mamsterla · 8th December 2005, 02:23

Thanks for the feedback to date. At a minimum I will check the cables to the battery and the high power connection on the right wheel well in the trunk.

Does anyone know the location of the fuel pump relay? If it is easy to change, I could do it myself and save the dealer headache. Anyone have a part number too?

-MA