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enginenerd Reader
9/9/19 11:55 a.m.

It was three months since I had purchased a car and I was getting the itch. To compound things, I sold our E30 the previous week, leaving a void in the driveway. (Not that owning 6 cars w/ a 2-car garage left much of one) I ended up on Craigslist and impulse bought this E39 530i:

I'm not sure what the plan is, and am still formulating a justification for buying this car. Here's a summary:

  • ~130k miles, 5-speed manual ZF w/ M54 engine. It moves under its own power, which was good enough for me. 
  • Rust free-ish body which is rare around MI. Car was allegedly from Florida (likely years ago) and the clear coat is roached. No evidence of major damage but it sure is ugly to look at. Forest green w/ a tan interior isn't helping anything. 
  • It's an electrical nightmare. MIL, SRS, ABS, DSC, and brake warning lamps on the dash. HVAC is completely dead. Driver's seat doesn't move. I'm sure I'll discover other broken stuff as I poke more buttons and/or smell electrical fire(s). 

So what's good? It was beyond cheap. It does run and drive decently well. Tires are old but have good tread. It smells like every other BMW from the Y2K era. That's about all I can say for now. 

I'm not quite sure what the plan is. I guess I partly bought this car to familiarize myself with semi-modern European cars which I have mostly avoided. I think it would be a decent winter beater if I can get the heater and seat heaters working. Maybe it really just needs an Ebay turbo kit for science. I dunno. Stay tuned. 



OjaiM5 Reader
9/9/19 12:03 p.m.

Cool color and it is a stick! Yes!

I say go for it, It has xenon headlights. If they are OEM - worth $400+ alone. 

The M54 is a great engine as well. 

enginenerd Reader
9/9/19 12:21 p.m.

The first order of business was addressing the stagnant driver's seat. I am of average adult male height and bought it from somebody that was decidedly taller. Being stuck in gangsta lean position coupled with the unsecured shift knob made driving challenging to say the least. Luckily I brought a terribad Harbor Freight tool kit with me. Minutes after signing the title, I tore apart the seat controls and checked the fuse panel.

One of the fuses related to the seat adjustment was blown. I replaced the fuse and of course the seat started moving. However, it reached a certain point of travel and blew the fuse again. I stripped back some insulation and realized the main power wire going to the seat control had pinched somewhere and had copper exposed. At a certain point of travel it would ground against the seat rail, thus blowing the fuse. One janky tape job later, I had a working seat adjustment (and resurrected steering column tilt control as a bonus). 

I drove home and after a few exciting moments realized the brake lights weren't working. All the brake light bulbs were burned out. I found some spares in the glovebox and replaced every one of them but...still no brake lights. I tracked down the wiring diagram and eventually diagnosed the problem as the brake light switch. I also pulled the HVAC unit to see if it was another easy fix but couldn't see obvious issues (apart from the broken/missing buttons) 

Sometime around this point, the car decided to start running rough at idle. The check engine light would come and go, but the variety of other warnings remained:

A quick check with the Torque app showed the following:

My shot from the hip is the MAF is faulty or there is a vacuum leak. I definitely needed more information. 

A $20 cable, some software of questionable legality, and a trip to my basement to dig up an old Windows 7 32-bit machine and I had full communication with all modules in the car. By full communication, I mean the computers were talking but in German, so I was feeling a bit left out. Google Translate came to the rescue and told me that a trip to the junkyard was in order for many, many sensors. All in all, there are somewhere around 15 active faults spread across a variety of modules. Here's a fun example of one of the error reports:


enginenerd Reader
9/9/19 2:09 p.m.

So I checked the local Pick N Pull and there are 2 530i's of the same model year. I'm going to scope it out tomorrow so hopefully they aren't too picked over. Here's the (rapidly growing) list of parts I hope to track down:

  • Brake lamp switch
  • HVAC control module
  • LF impact sensor
  • Yaw sensor
  • RF wheel speed sensor
  • Battery tie down
  • Reverse light bulb sockets 
  • Underhood battery cable
  • Misc. trim pieces, fuses, fasteners, etc. 

I guess the goal is to throw all these parts at the car, clear the faults, and see how many issues reappear. I don't plan to spend much of anything on this car but I probably should at least get it up in the air and have a look around at some point. 

AngryCorvair GRM+ Memberand MegaDork
9/9/19 3:33 p.m.

E38 and E39 have blower resistor module issues, so that could be giving you some of the HVAC woes.  i like your approach so far.  looking forward to updates.  friggin' E39's, when they're good they're soooo good.

enginenerd Reader
9/9/19 5:31 p.m.
AngryCorvair said:

E38 and E39 have blower resistor module issues, so that could be giving you some of the HVAC woes.  i like your approach so far.  looking forward to updates.  friggin' E39's, when they're good they're soooo good.

I quickly read a forum post on that blower resistor (FSU?) I think that may be the problem but I suspect the unit itself because there is no response from the system at all, and the panel is completely dead apart from button lights that come on when the rest of the dash is illuminated. I think when the blower resistor goes bad people usually get a weird response from the blower motor. Regardless, I'm going to try and grab one at the junkyard if they aren't all claimed. 

02Pilot SuperDork
9/9/19 5:47 p.m.

FSU failure is usually either the fan won't shut off or it only runs on high. Junkyard unit is as likely to be bad as the one in the car unless it's got a recent manufacturing date on it.

This thing doesn't have an aftermarket stereo, alarm, or remote start in it, does it? Any one of those poorly done (and they always are) could cause every electrical problem known to man.

enginenerd Reader
9/10/19 6:54 a.m.
02Pilot said:

This thing doesn't have an aftermarket stereo, alarm, or remote start in it, does it? Any one of those poorly done (and they always are) could cause every electrical problem known to man.

No aftermarket stereo, alarm, or remote start (that I'm aware of). I did find a cable that looks aftermarket under the dash above the pedals...it looks like a gps cable? I'll have to look into it a bit more. 

enginenerd Reader
9/10/19 7:08 a.m.

Before spending a dime on parts for this car, I decided to have a closer look. Last night I got the car up in the air and had a look around. Overall, it looks pretty good for a car that cost next to nothing.

The chassis is pretty much rust free, the brake pads have tons of life, and most of the suspension bushings look pretty good. I did find a few issues though:

Scary Issue #1: Rear brake line sketchiness 


Scary Issue #2: RR wheel has some play. I think it is mostly from this upper control arm bushing (ball joint?)



Other than that, there are a few small leaks that are so minor they aren't worth addressing. One front ball joint has a split in the boot so I will probably fix that as well. All in all, not terrible for what I expected to be a terrible car. 


artur1808 GRM+ Memberand Reader
9/10/19 7:22 a.m.

In reply to enginenerd :

"too rich" code might have to do with a faulty coolant temp sensor. Assuming the M54 is laid out the same as previous generations of BMW 6-cylinder engines, there should be two under the intake manifold; the forward-most one (usually a blue connector) sends signal to the DME and can be checked with a multimeter. The sensor that sends signal to the gauge cluster is independent of the one that sends signal to the DME.

I'd have to do some digging to find the exact specs, but basically you check resistance across the sensor cold and then check it again with it at operating temp. If it always thinks it's cold, it might perpetually adjust the tune to be rich. 

enginenerd Reader
9/10/19 7:28 a.m.

In reply to artur1808 :

Thanks for the advice. I didn't check them too thoroughly but the coolant temp values were believable when I was watching live data with the engine running. I'll add the temp sensors to my list of things to check over when I get around to diagnosing the rough cold idle issue. 

Brake_L8 Reader
9/10/19 12:13 p.m.

Brake, ABS and DSC all together are likely not a wheel speed sensor. The car is correct in thinking the RF speed sensor is bad, but in reality, the solder joints inside the ABS computer have failed and need re-flowed. They fail over time due to heat. Module Masters and a few other companies can do this fix for under $300.

I just dealt with a lot of random electrical issues in an E53 X5 3.0i. These cars (E38, E39, E53, E46) use K-Bus, an early variant of Canbus. Electronics are all networked and if one module isn't communicating properly, all sorts of weird stuff happens. I fixed all of the following by wiggling a harness under the e-brake handle:

  • HVAC panel not working properly
  • No reverse lights
  • Keyless entry remote "fob" not working
  • Turn signals and high beam indicators not showing on gauge cluster
  • Door chime not working
enginenerd Reader
9/11/19 2:24 p.m.

Well, I was getting a little overwhelmed by all the issues so I decided to focus on one at a time. I chose the lack of brake lights as the first issue to address. I thought this was the simple issue, but...

My process so far:

  • Replaced bulbs and checked fuses
  • Confirmed power at the brake lamp switch when key is in the run position
  • Confirmed jumper wire from power to signal pins at the brake lamp switch works to light bulbs
  • Decided the brake lamp switch was faulty. Replaced switch, but no change in symptoms

Time to get serious (and ask for help!)

E39's use a hall effect sensor as the brake lamp switch. There are 4 pins: a supply power w/ ignition, ground, a brake light test circuit that's supposedly unused, and the brake light circuit (that is spliced to the DME, light control module, ABS module, etc.) Here's the diagram:

So, I'm assuming there should be power on the S_BLS output when the switch is away from the brake pedal arm. I bench tested the suspected faulty switch, a junkyard switch, and a new aftermarket one. In all cases, voltage of that circuit is essentially zero regardless of switch position. I'm lost.

I hooked up some fancy software and can see digital inputs & outputs. The DME does see the brake light test circuit (S_BLTS above) working properly. I can even command the lighting control module to light the brake lamps w/o issue. Everything I try points me back to the switch, but I've tried 3 now and they behave identically. 

I know the GRM approach is to probably just use the test circuit as the input as that makes everything work, but I want to understand what's going on. Any ideas!?


enginenerd Reader
9/11/19 2:52 p.m.

In reply to Brake_L8 :

You are probably right on this. The car has a reman ABS module in it for better or worse. The two codes I'm getting for it are 1) FR wheel speed sensor and 2) yaw sensor. 

I'm going to try and look at the wheel speed sensor output eventually to confirm. 

AngryCorvair GRM+ Memberand MegaDork
9/12/19 4:48 p.m.

In reply to enginenerd :

is the pin for the non-behaving circuit pushed out of the mating connector such that it doesn't make contact when you plug it in?   i'm assuming you're energizing that circuit by probing the face, rather than back, of that pin.

enginenerd Reader
9/13/19 7:23 a.m.

In reply to AngryCorvair :

I keep thinking that it must be something along these lines as the connector appears ok. If I can figure out how to de-pin this type of connector I can confirm for sure. 

When I jump power from the supply to the intended output of the switch I am doing so from the back of the connector. 

enginenerd Reader
9/13/19 7:51 a.m.

So, a few updates...

I found one possible answer for several electrical issues in the form of dihydrogen monoxide. Remember this?

So I guess it's a common thing for E39 sunroof drains to get clogged and let water trickle down the A-pillars and into the floor pan. Unfortunately, it looks like the PO waited to tape up the sunroof until after he had a personal duck pond. When I bought the car, most of the carpet had dried so I didn't notice it. Pulling back the carpet, I realized that the 3" thick foam underneath was completely waterlogged and there was a puddle in the floor pan. Awesome.

So, where does that leave us? Well, I still don't have an explanation for the tail light issue. I'm not sure about HVAC because I haven't looked into it. However, the airbag light is on and the only code it registers is for the left side impact sensor...which now looks like this:

The ABS module has a code for the yaw sensor, which sits in the same area:

Considering both of these sensors were deep sea diving, I'm going to replace them. Looks like ~$30 on Ebay for both, so I think it's worth a shot. 

I also went to the local junkyard on a recon run a few days ago and picked up a few things. I couldn't get the sensors because they are under the driver seat which I couldn't get to move for the life of me. 


infinitenexus GRM+ Memberand Reader
9/13/19 9:52 a.m.

The E39 has always been my favorite body style of BMW.  Glad to see you're fixing one up.

AngryCorvair GRM+ Memberand MegaDork
9/13/19 9:56 a.m.

i'm looking at that pile of fuses thinking "sweet, he got a jigsaw puzzle!"   i wore the wrong glasses today.

TurnerX19 Dork
9/13/19 1:40 p.m.

Dihydrogen monoxide is a very dangerous chemical. We must stop it from falling out of the sky! Desertification for all!

enginenerd Reader
9/14/19 11:59 a.m.

The brake light issue is solved! 

I (finally) realized that the circuit shown below was shorting to ground. As you can see, the brake light switch output is tied into a couple components including the ABS controller, DME/ECM, and light control module. 

I went and tracked down the splice, called out as X181 above. Pulling leads of the X181 splice, I was able to determine which one was grounding. I reattached all leads sans the problem child. Push the brake pedal and now there is 5V going to the LCM which lights the tailights. Success! Here's that splice found under the seat: (Also...holy crap removing the seat caused an insane amount of new faults.) 

So I now knew the wiring going to the LCM and brake light switch was good. To determine which branch was faulty, I looked at the digital inputs & outputs at the DME and ABS module. DME saw both the brake light circuit and test circuit, where as the ABS module saw nothing, thus being the unconnected & faulty circuit. 

I pulled the connector at the ABS module and the short to ground went away so it looks like that ABS module is shorting internally. It's a reman unit from BBA remanufacturing. It has a lifetime warranty so we'll see if they honor that (doubtful). For now, I'll leave that lead disconnected, or maybe just disconnect the ABS module as it doesn't seem to be doing much. 

GarageGorilla Reader
9/14/19 3:46 p.m.

Awesome work OP. Also, awesome score on the car! Please keep this thread going.

enginenerd Reader
9/16/19 8:47 a.m.

So, this car has the unholy trinity of contributions to electrical issues: poor stereo install, water damage, and Germany. Surprisingly, only the last one was the root cause behind the non-functioning brake lights and the HVAC not working. Both of these problems are now solved! 

You read about about the brake lights in my earlier tedious posts with wiring diagrams you never wanted to see. The HVAC took me a while to figure out. The IHKA (BMW-speak for climate control panel) was entirely non-functioning. It would get power but every time I turned the key on it would blow a 15A fuse. I figured it must be a short and started disconnecting various connectors and pins to narrow it down. 

I removed one pin and the fuse stopped blowing. I figured that must be the circuit with a problem and it led me here:

Turns out that wasn't the issue...but I learned a lot. Eventually I started reconnecting things one by one. After each circuit was added I would turn the key and check. Eventually, the HVAC panel functioned properly! 

See that one loose wire hanging out? That's the culprit. It's for an auxiliary water pump which I assume is to keep the heater functioning if the engine is warm but not running. Apparently it is shorting somewhere so I will need to track that down. Also, the car thinks it's -40F out so it's heating the daylights out of the mirrors, wipers, etc. 

So, lots of things to still fix but I've fixed the two things I really deemed necessary (apart from the mechanical issues mentioned above.) I'm pretty sure the HVAC and lack of brake lights are what got this car sold so cheap. So far, my only expenses on this car have been an $8 junkyard run. I'll probably start ordering some parts soon!




rothwem New Reader
9/16/19 8:57 a.m.
enginenerd said:

Also, the car thinks it's -40F out so it's heating the daylights out of the mirrors, wipers, etc. 

It might be obvious, but if its reading -40F, the problem is the outside temp sensor.  I think its under the front bumper somewhere, I had the same issue on my E83.  They can get scraped off or broken pretty easily, luckily the part is ~$30.  

Anyways, glad to see this car being fixed up.  The E39 is one of my favorite BMWs, they're just solid feeling cars.  

enginenerd Reader
9/16/19 9:30 a.m.

In reply to rothwem :

Yup, I figured it likely would be. It's now living in the engine compartment as it looks like the mount broke. I'm going to see if I can grab one the next time I visit the junkyard. 

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