Hi everyone,

I’m chasing a stubborn "No Communication with DME" issue on my UK-spec 2014 BMW 4 Series Coupe (420i, N20 engine, manual transmission, RHD). This all started because I re-flashed (BM3) before my MOT after sitting over the winter and suffering a severe battery drain, the car went into a hard no-crank, no-start state (everything else seems to work fine)

When hooked up to ISTA+ (using an ENET cable to USB-C adapter, hence why top-right KL15/KL30 fields show standard ENET dashes), the DME remains solid RED on the Control Unit Tree.

The car has a total of 51 permanent faults after clearing historical noise. Almost every responding module (FEM, DSC, EPS, ICM, REM, KOMBI) is healthy but throwing network errors stating: "No message... transmitter DME/DDE". Additionally, there is a hard active fault for ⁠8040B1⁠ (Wake-up line to the intelligent battery sensor IBS: Short circuit to B+ or line disconnection).

To isolate this issue, I have performed extensive diagnostic steps with the following definitive outcomes:

1. A brand-new 96Ah Exide AGM battery has been installed and is kept charged using a CTEK charger.

2. DME Hardware is GOOD: The DME was removed from the car and sent to a bench specialist (Martyn at ECUWorx). It powers up and communicates perfectly on the bench rig, ruling out internal board failure or water damage. However due to not having the right harness he was unable to validate the Key to FEM to DME communication.

3. Integrated Supply Module (IVM) is NEW: Replaced the engine bay IVM module completely. Zero change; DME remains entirely non-responsive on the car's loom.

4. IBS Sensor Isolation: Unplugged the 2-pin black data connector at the negative battery terminal to check if a shorted IBS chip was dragging down the wake-up line. The DME stayed red.

5. Engine Ground Circuit is GOOD: Ran a heavy-duty jumper lead directly from the chassis factory grounding stud on the strut tower to a clean, bare aluminum structural section on the engine cylinder head. Rerun of the ISTA vehicle test showed no change (DME stayed red), completely ruling out a snapped or corroded lower engine ground strap.

6. Main Under-Car Power Cable is GOOD: Tested the main B+ bolted power supply terminal in the engine bay compartment using a power circuit probe. It reads a clean, live 12V, proving raw battery juice is successfully travelling from the boot to the front of the car.

7. All Module Fuses (FEM, REM, EBox Fuse Panel, Trunk Power Distribution Box) are GOOD: Probed every individual blade and maxi-fuse, all fully intact and passing voltage correctly on both sides.

Current Status & Next Steps:
Battery power is available, the block is perfectly grounded, the fuses are good, and the DME hardware functions perfectly on a test bench. Yet, when plugged into the car, the engine bay remains a complete communication dead zone.

My next steps are to cleanly isolate the DSC (ABS) module plug to ensure a fried module isn't choking the PT-CAN line, and to check if the Terminal 15WUP (Wake-up) 12V signal from the FEM is actually reaching the engine loom. however struggling to disconnect the ABS Harness.

Has anyone encountered a similar issue on their f-series following a failed flash or where the FEM fails to send the wake-up voltage to the DME while leaving the rest of the car awake? Any guidance on specific wiring pins or hidden fusible links to check next would be incredibly appreciated!

ISTA screenshots attached for additional context, more can be sent too.

Morning Ray

Welcome to the Forum

Seems you have the right tools with ISTA I would still want to confirm the FEM DME signal

The fact you have 51 permanent faults indicates to my old head you have some Bus issues which are preventing communication BMW are fond of using a twisted compressed joint system sealed in a clear soft plastic sleeve. Over time they can sweat and corrode internally if you expose a join and it looks black that's corrosion (attached is a picture of the Bus system in my X5) the pic with my hand in shows the Bus system Green and Orange wires I spent a morning remaking and soldering the joints and sealing them in shrink wrap. Once all the loom communication is back you may have more success with clearing stubborn faults. Check the continuity FEM to DME all pins

Good Luck hope this helps

Dave