97 540i unusual electrical problem.

[TheFanatic]

As the title states I have a 97 540i 6 speed with a rather unique problem. It's very intermittent and I cant always duplicate.

While driving the car will run normally but when I got to shift gears and the rpms drop between 1000-1500 the headlights will dim, the dash will dim, the radio turns off and then on again and the traction control light and abs light will flicker. Once below 1000rpm everything returns to normal. It does not happen at any rpm other than that. I does not happen while engine braking only when the engine load has been removed and rpms drop. During the failure the engine doesnt miss a beat and runs as nothing's going on.

I've checked grounds, I've checked fuses. the links on this forum that lead to wiring diagrams dont work/load for me which would have been a huge help.

Also the problem got worse for just one trip to work. During this episode the whole car would shut off for a split second including the engine. I could also hear the relays clicking in the passenger footwell area. I've got 4 videos that help show what I'm talking about. Any help would be greatly appreciated.

Ive replaced the dme relay btw. No change. These are links to the videos I have that show the problem while they're going on. They're short but they show the problem well. In the last one you can hear the relays I'm talking about clicking in rhythm and the dash lights flickering in unison.

https://youtu.be/mYSOEPjO4GA
https://youtu.be/ZKCHqwARWFM
https://youtu.be/siGsqqtBZyY
https://youtu.be/PMqNJJQJsvQ

[JimLev]

Welcome to the forum.
Could be a few things.
Ignition switch
Corroded fuse box under front pass side carpet
Loose battery cable

Whats that CEL on for??

[jclausen]

The radio going on and off is a classic sign of the ignition switch if has not been replaced I would just do it out of preventive maintenance I did mine as soon as I got my car.

[jicaino]

Flip your sun visor down and open the mirror lid to light the courtesy lights and see what happens. I'm leaning towards ignition switch as the majority here. When this thing occurs, are you getting the transmission failsafe message? the EGS limp mode is usually triggered when a bad voltage regulator allows spiking over 15v disturbing the data line.

[TheFanatic]

Flip your sun visor down and open the mirror lid to light the courtesy lights and see what happens. I'm leaning towards ignition switch as the majority here. When this thing occurs, are you getting the transmission failsafe message? the EGS limp mode is usually triggered when a bad voltage regulator allows spiking over 15v disturbing the data line.

I dont have an automatic so there is no transmission fail safe to my knowledge

[TheFanatic]

Welcome to the forum.
Could be a few things.
Ignition switch
Corroded fuse box under front pass side carpet
Loose battery cable

Whats that CEL on for??

I just typed a ton for it all to be deleted when I hit the wrong button lol.

Anyways check engine light is on because I have no cats or o2 sensors, will be getting those fixed this summer hopefully.

I did the ignition switch test and it showed no signs of failure and I dont like throwing parts at it so I didnt replace it. I have not checked the fuse box under the passenger seat but will look this weekend and report back its condition. To note I have had zero issues with moisture or water inside the vehicle but will check anyways.
The battery cables are tight and corrosion free as well as other grounds and cables that I can see both in the engine bay and trunk.

I'm going to add that this problem only seems to happen when its above freezing but isn't a guarantee that it will happen because of how intermittent this problem is.

[jicaino]

Engine failsafe or weird errors that go away (in lieu of the absent EGS failsafe which was the main telltale)? It might be a bad voltage regulator spiking when hot (or above "warm" on the operating temp range scale). When it's acting up unplug the VR and start it, drive without exceeding 1500 rpm and do not turn any consumer on. If it cures the symptoms, then you may have a bad voltage regulator.

[mattmar1]

jicaino has a good point, alternator output. any decent parts house can test your charging system, usually for free. if you get a good guy and explain what youre seeing, he can do more than a generic "yup its charging" test. most have the newer testers which perform a ripple test on the alternator as well. or if you are adept with a multimeter, you can do it yourself. water incursion in these vehicles isnt always obvious. the pad under the carpet is pretty thick, and drain/barrier leakage can puddle under it and not show any obvious signs.

[TheFanatic]

Engine failsafe or weird errors that go away (in lieu of the absent EGS failsafe which was the main telltale)? It might be a bad voltage regulator spiking when hot (or above "warm" on the operating temp range scale). When it's acting up unplug the VR and start it, drive without exceeding 1500 rpm and do not turn any consumer on. If it cures the symptoms, then you may have a bad voltage regulator.

I have a battery and alternator tester (amp and voltage not a bench tester. I'm a diesel mechanic) at work and will test once I'm clocked out. One of my original theories was that it was the alternator starting to go out and there was a switch of some sort that when the engine rpms decreased it changed somehow and at that "switch" moment (roughly 1250rpm give or take) is when the failure would happen. I dismissed it because I have no issues with idling or low rpm voltage and figured if it was the alternator it would happen at low rpm all the time.

I will try unplugging it but if I shut the car off the problems more than likely wont come back once I start the car again. The first time it happened it took almost two weeks for the symptoms to reappear. I do believe it is temperature related in some way though.

Also would anyone know where the good links for the wiring diagrams are? The FAQ and commonly asked questions section links dont bring up a working website anymore.

[jicaino]

I had the same thing going on. To make it worse, it would fail sporadically and randomly, only when on the hot end of the operating temp range, or when high loads were involved (eg very spirited driving around obstacles, like that) I have had the alternator recently redone so I ruled it out and it turned out to be a voltage regulator that had one diode allowing a spike from time to time. It will do all sort of funky stuff when it spiked, and the spike could not be repeated in test conditions until it got worse.

[edjack]

[QUOTE=TheFanatic;
Also would anyone know where the good links for the wiring diagrams are? The FAQ and commonly asked questions section links dont bring up a working website anymore.[/QUOTE]

Try this site: https://www.newtis.info/tisv2/a/en/e...nctional-info/

[TheFanatic]

Alright so a bit of an update. I pulled the carpet and there was no corrosion or loose terminals. I swapped over the unloader relay with a known good one that I had and no change. I also tested the voltage regulator the way that jicaino had suggested and the problem had persisted.

That being said it I was slightly more prepared when the problem happened I've tested the ignition switch using the passenger mirror light no change. I did what I could to see if there was a specific condition for the problem to appear or go away. When the problem was going on I would rev the engine and it didnt matter what rpm the engine was the problem remained. Today was also well under freezing so it isn't a outside temperature related issue.

That being said I've went over to a buddies place and we pulled a ton of wiring diagrams from Mitchell. Looking over them it seems that the most common point of power between all the effected system is the ignition switch just not the same leg as the mirror lights.

There are 4 run/start legs on the ignition switch. Terminal point 3 gives ignition power to the engine control module, HVAC module, light module, instrument cluster (both with and without the IKE), terminal 15 on the unloader relay and the closed circuit current cutoff relay (which controls interior lights system and fuse F13 (seat and steering wheel adjustment switches basically)). So although testing the ignition switch using the mirror light works for most applications its possible it doesnt on mine because only one leg of the power system is failing not the whole switch.

I've got the new one ordered and will report back if it fixes it or not. It may take a bit with as intermittent this problem is.

[jicaino]

Alright so a bit of an update. I pulled the carpet and there was no corrosion or loose terminals. I swapped over the unloader relay with a known good one that I had and no change. I also tested the voltage regulator the way that jicaino had suggested and the problem had persisted.

That being said it I was slightly more prepared when the problem happened I've tested the ignition switch using the passenger mirror light no change. I did what I could to see if there was a specific condition for the problem to appear or go away. When the problem was going on I would rev the engine and it didnt matter what rpm the engine was the problem remained. Today was also well under freezing so it isn't a outside temperature related issue.

That being said I've went over to a buddies place and we pulled a ton of wiring diagrams from Mitchell. Looking over them it seems that the most common point of power between all the effected system is the ignition switch just not the same leg as the mirror lights.

There are 4 run/start legs on the ignition switch. Terminal point 3 gives ignition power to the engine control module, HVAC module, light module, instrument cluster (both with and without the IKE), terminal 15 on the unloader relay and the closed circuit current cutoff relay (which controls interior lights system and fuse F13 (seat and steering wheel adjustment switches basically)). So although testing the ignition switch using the mirror light works for most applications its possible it doesnt on mine because only one leg of the power system is failing not the whole switch.

I've got the new one ordered and will report back if it fixes it or not. It may take a bit with as intermittent this problem is.

I like a documented, well conducted study of symptoms.

You could also try undoing the column cover and see if you can take out the ignition switch and inspect the contacts, or if you just replace it, do an autopsy on the deceased one to see what was causing those symptoms.

[TheFanatic]

Alright well I hate having a misdiagnosis but it seems the ignition switch was not the source of the problem. So I bought the adapter to my friends ethos pro for the engine diagnostic plug, and once that comes in were going to go into the computer and hope that it can give me a clearer picture of what the problem is. Once I'm able to see what the computer sees I hope I will have an answer.

One thing I am sure of is it happens around 1500rpm or less and only when I'm off the throttle what parameters change for those specific conditions I'm not sure, (idle air control valve maybe?). Wiring diagrams unfortunately dont tell me computer programming.

This problem brings memories to mind where I had a downstream O2 sensor that the housing was cracked on, so when it would get wet cylinders 2,4,6,8 would short out and misfire. That took me a while to figure out as well. So I believe I have a component failing and causing these issues. I'm just having to go through hell and back to figure out which one it is.

[mattmar1]

when you checked the grounds, which ones did you check? theres the trunk, below the a pillars at the front doors, one connection at the passenger side fenderwell near the strut, a frame to engine strap, and 2 fenderwell ground shoes front of the fenderwells just rear of the headlights. had a similar issue once, turned out the be the strap near the passenger front strut. headlights would flicker quickly, radio would go quiet for a split second, lights would flicker, engine would drop rpm. all this would happen just for a split second, it always recovered.
as far as testing the alternator, may i suggest one more test? hook up your meter in ac mode and see what kinda ac ripple you have with the engine running. should only be in the low MV range.

[TheFanatic]

I think part of my issues might have been I was testing the alternator when the problems werent actively going on. Maybe there is some weird voltage issues idk. I'll check again once while they're going on.

As far as grounds go every one I could find I checked. The ones under the carpet included.

Also new discovery. Craziest thing. It doesnt happen when I slowly bring the rpms up and then rev it just shen rev from idle... make sure to watch until at least after 16 seconds. That's when it really gets interesting

https://youtu.be/zhwTeg6nL9Q

[mattmar1]

watched the video...thats one strange issue going on there.

[Astrocyte]

Have you load tested the battery yet?

[jicaino]

This is the voltage regulator. 100% sure.

- - - Updated - - -

that's a failing VR on a good alternator. Replace the VR before it toasts modules and you need to replace the whole alternator.

[edjack]

Might try monitoring the battery voltage when the anomaly occurs.

You have an exhaust system leak.

[Astrocyte]

It does sound like a regular but he needs to cover the basic stuff first. 5ers go bonkers with a worn out battery.

[jicaino]

It does sound like a regular but he needs to cover the basic stuff first. 5ers go bonkers with a worn out battery.

Not when you rev it. If the car does that when you rev it it's a failing voltage regulator. A very easy fix at this stage, if he keeps "diagnosing" will eventually develop in greater issues that costs far more than a voltage regulator (should the VR diagnose be off, which is a 5% chance with that symptom)

[TheFanatic]

Jicaino- Yeah I'm going to agree with you. When the problem is found there is no point in continuing to look for another. All I know is thank God I have the air cooled version from the non-vanos engine. Cause man is that water cooled alt expensive. Once I was able to monitor voltage when driving it became clearer that the regulator was slow to react and starting to fail. Its original so at 270k miles I cant complain with its longevity.

Edjack- yes I know. It's coming out right where my catalytic converters no longer are. It's on the list of things I want to fix this summer if I deside to keep the car. Also I was able to use the dashboard diagnostics to monitor the voltage and I could confirm it was dropping as low as 8 volts when everything would glitch (makes sense seeming the car needs at least 9.6 to survive). What confused me the most was if the alt wasn't keeping up for that short bit why wasn't the battery taking over and filling in that gap. So I removed the battery to check for any external issues but found none. Conveniently I haven't had the problem since so obviously there was some connection problem that a voltage drop test couldnt find and wouldnt cause any starting issue.

Astrocyte- battery was replaced last year and I tested it around when these problems started. It has 839cca so about 97%.

[jicaino]

Jicaino- Yeah I'm going to agree with you. When the problem is found there is no point in continuing to look for another. All I know is thank God I have the air cooled version from the non-vanos engine. Cause man is that water cooled alt expensive. Once I was able to monitor voltage when driving it became clearer that the regulator was slow to react and starting to fail. Its original so at 270k miles I cant complain with its longevity.

Edjack- yes I know. It's coming out right where my catalytic converters no longer are. It's on the list of things I want to fix this summer if I deside to keep the car. Also I was able to use the dashboard diagnostics to monitor the voltage and I could confirm it was dropping as low as 8 volts when everything would glitch (makes sense seeming the car needs at least 9.6 to survive). What confused me the most was if the alt wasn't keeping up for that short bit why wasn't the battery taking over and filling in that gap. So I removed the battery to check for any external issues but found none. Conveniently I haven't had the problem since so obviously there was some connection problem that a voltage drop test couldnt find and wouldnt cause any starting issue.

Astrocyte- battery was replaced last year and I tested it around when these problems started. It has 839cca so about 97%.

Having recently replaced a failed water cooled alt I agree with you wholeheartedly. It was friggin expensive, like half of the price I paid for my 523i expensive.

[TheFanatic]

Having recently replaced a failed water cooled alt I agree with you wholeheartedly. It was friggin expensive, like half of the price I paid for my 523i expensive.

Oh man brutal. Not a bad price on a 523i though!

My last car was a 95 Nissan Maxima but cost me a whole $86 for that alternator