E46 - N42b18a , no crank, no start, nothing. Details below

ChrisXtreme · Mar 1, 2025

first of all, sorry about the image quality i was working on the car until late.
Its an e46 - 2003 318i, with the n42b16 engine.
the car suddenly didnt start one day. No crank, not clicking. Nothing happens when i turn the key. I changed the fuel pump, checked ALL the fuses inside and outside, replaced the COMPLETE wiring, changed ALL the sensors. And when i say all, i mean literally everything.
- What i do know :
I can turn on the ignition, lock the doors with both keys, tried 4 different batteries, the alternator is new as well.

when the ignition is on the yellow DSC light is on and will stay on. The handbrake light also stays on and the tempterature gauge will go straight to max in the red zone.
my code reader and inpa can no longer communicate with the ECU. I just get an error message. I can communicate with the EWS and other modules.

ive been switching parts for months now and i think my final guess is a fried ECU, but if you have any ideas please let me know. Im begging you. Thanks!

UPDATE :

So i took out the cluster this morning just to take it apart and double check and just for the “fun” of it i tried starting the car without the cluster and it started cranking. Just crank no start tho.
i started disconnecting stuff one by one to try and start but nothing. I put the cluster back in hoping maybe now i can read codes but still no communication. However the car now at least cranks. The temp gauge still shoots straight to red and the DSC light is on as well.
checked the fuel pressure and it is 0. I can hear the pump click but it wont prime so i believe its getting power but no signal from the DME.
Took out the DME and gonna send it to a shop as soon as possible since Im losing sleep over this.

Ill keep you updated and post the results once ive got to the bottom of it. Cheers. Also keep sharing ideas if you had something like this in the past and got it fixed.

Alan G · Mar 2, 2025

A fault code scan would be the first thing to do.
Something electrical i would think as the temp gauge is in the red that could be telling the ecu not to let the car start as it is too hot overheated.

ChrisXtreme · Mar 2, 2025

Yes but i cannot do a fault code scan because the scanners cannot communicate with the ECU. I just get an error message, saying to make sure the device is plugged in correctly and the car is set to ignition.Took it to a shop, They can’t scan it either. Tried 3 different scanner at home and They all do the same. This is why my last idea is a dead ECU. I own three e46 cars and never got into such trouble its killing me.

gonna send the ECU unit to a specialised shop to test it, once i get home from work but thats 2 weeks from now as i work abroad. Thats why i thought id ask if anyone ran into such a problem.

Nobody · Mar 2, 2025

Get a pinout for the ecu, it isn't getting power or an earth.

ChrisXtreme · Mar 2, 2025

For some reason i have a feeling something else like a faulty module is causing a short. Ill report back once i got my DME tested. Thank you!

Nobody · Mar 2, 2025

Trust me, 99.9% of the time you can't talk to an ecu it's a power/earth issue.

Does your eml come on? Guessing it doesn't.

ChrisXtreme · Mar 3, 2025

Nope, EML does not Come on…….

Alan G · Mar 3, 2025

+1 on the above.
Worth checking out first.

Johnnyroper · Mar 3, 2025

Even with a good relay it doesn’t prove power supply is good, there could be no power through relay contact. Needs checking with multimeter.

Nobody · Mar 3, 2025

Pinout for the ecu and check power and ground terminals. Will be an easy one to diagnose.

ChrisXtreme · Mar 9, 2025

Quick update:

I took the whole DME package ( DME , cluster, EWS, ignition switch) from a different E46 and the same thing is happening. Car cranks, fuel pump does not prime, temp gauge shoots straight to red and the yellow DSC comes on. Nothing changed. This means the DME is fine right?

So the right answer must be a bad ground or the DME not getting juice. I got my meter and will try to check every possible point. Tell me if Im missing something. Or more advice on How to check the pins on the DME. Thank you for staying with me!

payno · Mar 10, 2025

When the temp gauge goes strait to the red it means its not getting a signal from the ECU/DME.

ChrisXtreme · Mar 25, 2025

UPDATE: for those who are Still interested. The problem is not solved yet. All the cables and grounds are fine. I ended up taking it to a shop, because i dont have enough time to work on it. Its been there for 2 weeks now. They have no idea whats wrong with it. I dont know What to do at this point. They are Still trying to find the problem. I will post the results……

E46 - N42b18a , no crank, no start, nothing. Details below

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