E90 Electrical issues, possibly DME loosing power

DublinDilbert

Hi All,

Was driving home this evening and the dash light up like a Christmas tree, dsc warnings and engine power completely dropping in and out. As the engine power was coming and going i could hear a relay behind the glove box turning on/off. Managed to get the car home, it eventually died in the drive way, engine light on + 5 other warnings.

When I got inpa, hooked it up, no DME errors at all. Car started and run's fine. I checked the DSC system for the other errors and got one error (just set this evening) that the DME was not sending information over the CAN bus.

All i can deduce is that the DME was loosing electrical power or something similar. Not sure how the fuel pump is controlled on these, but it sounds like the fuel pump relay was dropping in/out too. Car started and ran fine then, took it for a long spin not a bother, hit lots of speed bumps, encase its a bad electrical connection.

No other power issues with the car, checked battery / alternator and all fine.

Anyone seen anything similar on these?

Onwardandupwar

DublinDilbert wrote: »

Hi All,

Was driving home this evening and the dash light up like a Christmas tree, dsc warnings and engine power completely dropping in and out. As the engine power was coming and going i could hear a relay behind the glove box turning on/off. Managed to get the car home, it eventually died in the drive way, engine light on + 5 other warnings.

When I got inpa, hooked it up, no DME errors at all. Car started and run's fine. I checked the DSC system for the other errors and got one error (just set this evening) that the DME was not sending information over the CAN bus.

All i can deduce is that the DME was loosing electrical power or something similar. Not sure how the fuel pump is controlled on these, but it sounds like the fuel pump relay was dropping in/out too. Car started and ran fine then, took it for a long spin not a bother, hit lots of speed bumps, encase its a bad electrical connection.

No other power issues with the car, checked battery / alternator and all fine.

Anyone seen anything similar on these?

Yep seen the exact problem before chased my tail with in for about 3 days pulled out the dash done everything couldn't find anything wrong anywhere apart from in one priticular area. After 3 days and loads of labour I foud the source of the problem.

Nissan doctor

Onwardandupwar wrote: »

Yep seen the exact problem before chased my tail with in for about 3 days pulled out the dash done everything couldn't find anything wrong anywhere apart from in one priticular area. After 3 days and loads of labour I foud the source of the problem.

Bit pointless if you don't tell the OP what it was.

DublinDilbert

Nissan doctor wrote: »

Bit pointless if you don't tell the OP what it was.

Ahhh, that would ruin the fun

I assume he means its pointing towards the DME relay, maybe he can confirm. I picked up a new one this morning anyway, will fit in a few mins. I'll also check the DME wiring and grounds.

I came across this last night, seems to indicate the same issues.
http://www.e90post.com/forums/showthread.php?t=545976

Onwardandupwar

Yes I'm pointing towards that relay but it's not the relay as such remove the relay and check the wiring underneath where all the relays are in the box under the wipers on the right hand side, also just tight up like close the connections tighter that the relay going into it is a snigger fit. If u need anymore detail pm it's hard to explain what I'm trying to say but u get my idea

DublinDilbert

Onwardandupwar wrote: »

Yes I'm pointing towards that relay but it's not the relay as such remove the relay and check the wiring underneath where all the relays are in the box under the wipers on the right hand side, also just tight up like close the connections tighter that the relay going into it is a snigger fit. If u need anymore detail pm it's hard to explain what I'm trying to say but u get my idea

Super, i know what you mean, going to have a look at it now. I'll clean down all the terminals and make sure they are a good fit. Will go over the ground connections too, which are in behind that on the bulk head.

DublinDilbert

Connections looked fine, gave them a clean down and re-set the contacts. And installed the new relay. I'm guessing the issue might lay else where, but we'll see...

Onwardandupwar

No no no I didn't mean the relay check the wiring under the relay in that box lift it all up that's where ur problem lies. It would make u think it's the relay it's underneath there a cant remember the exact wire but just under the relays take the wiring and examine carefully 100% garenteed ur problem is under there

DublinDilbert

Onwardandupwar wrote: »

No no no I didn't mean the relay check the wiring under the relay in that box lift it all up that's where ur problem lies. It would make u think it's the relay it's underneath there a cant remember the exact wire but just under the relays take the wiring and examine carefully 100% garenteed ur problem is under there

On this model the DME relay is buried upside down in that box, so I had to un-clip the wiring + relay socket from the carrier and slide the whole lot up. So I checked over the wiring + relay socket while it was all pulled out.

You may well be right that there is a problem with the wiring there, but i just couldn't see it when i was in there. I'll have to go in for round two

The other thing I can think of is the battery cable coming form the boot to the DME directly, apparently these can suffer from corrosion also.

Onwardandupwar

Yes they can I tought u had checked that but my bet is in the box u where right what u where doing with everything out be carfull tho disconnect the battery when checked it as if u arc that power wire that's loose it's bye bye ecu. I've seen that happen so just take your time

DublinDilbert

The power supply to the dme finally went today. Dme is completely dead in the water now. Have checked and tested all grounds, both power supply cables to it and all look fine.

Starting to think it might be an internal fault with the power supply inside.

Anyone any ideas before the ecu gets opened up??

DublinDilbert

Just to finish off this thread. Went back at it this morning, checked all wiring 10 times, still nothing from the DME, no CAN comms or anything else. Just about tried everything I could. Had DME in an out so many times as i checked everything including the CAN bus etc...

So decided the ECU had to be opened up, i done this very gently, as i'd just found out the price of a new one from Frank Keane ( €1075+VAT+Coding ). After the bolts were removed, it has held together with rtv (silicone) and some sort of glue. I got the back off, there was a small bit of corrosion, but nothing too bad. So then I decided I had to completely remove it from the metal housing, the big screw drivers came out and after much prising, it finally popped out.

When I looked at the underside of the PCB there was a good bit of corrosion around one part of the circuit, see attached picture. So I decided to give it a clean up, when I just touched it with alcohol and a tooth brush, pin 8 just fell off the IC, it was only been held on by corrosion. There was no way to repair the IC, so after a bit of googling the part number (B57554), I saw it was just a standard comparator like an LM2903. Don't have many parts at home, so went back over to the office, found a roll of LM2904s and said one of them will do, technically its an opamp ;-) I still hadn't much hope, but always been one for lost causes I decided to swap over the IC & clean up the PCB.

Drove back home, didn't honestly think it was going to work. Plugged in the ECU, ignition on and the engine light came on (wasn't on before). Pressed start and it just started right up ;-)

So I re-assembled the ECU, put everything back together and it flying along no problems. I was still a bit uneasy, cause without a schematic I'd no idea what part of the circuit I had just repaired. So this evening I was just googling and found an old Bosch schematic off an E34 (http://www.e34.de/tips_tricks/motronic/m1_3.pdf). When looking at the schematic, I spot the same IC, with the same components :eek: It controls the re-set line to the main CPU, bingo :-)

Man of Aran

Great post and well done to you !

Necessity ( and saving E1075+) is the mother of invention, eh !