2001 e39 540 DME nightmare

[Phillyflyboys]

Tried doing an advanced search but not much found, any feed back or ideas from the forum would be appreciated. M62 w/ vanos and went into "limp home mode" far from home, stuck towing to unknown indy mechanic two weeks ago. New throttle body diagnosed and installed, drove it a long way home. Car sat for a week (not daily driver) and went back into limp home mode next time I started her up. Had the car towed to local trusted guy and he diagnosed leaking thermostat that ran down wiring harness and corroded the DME, thus sending false codes and putting the car into limp home mode. I see used DME's are available on the world wide webs but what is with the programming of them? My guy refuses to deal with them but DME's brand new from BMW along with a new wiring harness has me in the price range of, well, dumping the car to a parts guy. OVER A THERMOSTAT!!! What's the story with reprogramming DME's? It seems like only a secret society of hackers know this trick...

[Phillyflyboys]

Well, it's been a while but it took a while to get this sorted out. Considering the fix I figured I'd update anyone who may read this after they came across the similar M62 thermostat bust. I found a DME repair specialist, Specialized ECU Repair (ECUdoctors.com), who saved my ass. $475 and they swapped out my damaged DME with a rebuilt unit. All synced up to my keys so the factory alarm worked. Five year warranty on the new DME included.Plus via car-part.com I found All Import Auto Parts in Fort Worth who sent we a used wiring harness with a 90 day warranty for $150. I went from $3300 to south of $1900 after my mechanic installed all the stuff. Whew...

[bmwdirtracer]

Glad you fixed it, but I'd sure as hell like to know how a leaky thermostat could get the dme wet in an E39 540. They'r four feet away from each other, and the dme lives in a sealed box. Can anyone explain this to me?

[mhunter29928]

Capillary effect? Like a tree gets water to it's leaves? I've heard of it. Never seen it though.

[JAPCRP]

Ive never seen it on a bmw e39 but its really common on mercedes. The transmission oil makes its way through the data plug connecter and into the wiring harness inside the wire thats insulated !! Up through the harness and into the main transmission ecu. Completely full of ATF. Goes into trans limp mode or (trans fail safe) on the bmw's.
The only way it could be possible was if the thermostat control sensor or coolant temp sensor allowed the water/coolant to travel up through its pin connectors and in through the wiring. Its possible but just something i havent come across yet.

[White94RX]

I've seen it. Thermostat leaks through the connector. Coolant travels up the harness to the DME.

[Phillyflyboys]

I've seen it. Thermostat leaks through the connector. Coolant travels up the harness to the DME.

This is it. The thermostat leaks up through the connector due to the pressure created by the heated coolant. Over time the coolant wicks all the way through the harness until it hits the DME. Rule of thumb, if you have an M62 replace your thermostat as preventative maintenance just for the hell of it.