Editing Openai/6940b2df-db80-8003-b707-4cc5cbedf6d9 (section)

=== ## ===
# Key out
# Trunk open
# Let car sit 10 minutes
# Disconnect negative battery terminal (IBS stays attached)
# Disconnect positive terminal

Battery comes out of the car.

==== - Old A46 off ====
* Old cables exposed
* Leave the old positive cable loosely in place for now (it becomes your routing guide)

==== Up front, you will disconnect three points (varies slightly by build): ====
# Underhood jump post - Remove red cover - Remove nut - Lift cable off
# Starter main terminal - From underneath - 13 mm nut - Remove cable and insulate it immediately
# Any intermediate junctions or brackets - Note routing - Photograph before removal

⚠️ Do not let the cable touch ground once disconnected.

==== Under the car: ====
* The cable is retained by clips and brackets
* Remove them one by one
* Do NOT yank the cable out

Key rule:

: 

BMW routed it that way for heat and abrasion reasons.

==== - Pull it rearward out of the trunk ====
* Inspect it (you’ll likely see heat damage or stiff insulation near the lug)

Set it aside uncoiled — you’ll use it as a length and routing reference.

==== ### ====
* Start in the trunk
* Follow the exact OEM path
* Use all factory clips and brackets
* No tight bends
* No contact with exhaust or moving parts

If the cable feels “short,” it’s routed wrong. Do not force it.

===== This prevents tension at the rear A46. =====
# Starter terminal: - Cable flat - Torque snug (BMW spec ~13–15 Nm depending on stud)
# Jump post: - Clean contact - Torque correctly
# Any junctions or brackets reinstalled

==== Now that the cable is correct, this part will finally succeed. ====
# Place new A46 in position
# Install main positive cable lug FIRST - Flat - No rocking - No washers
# Install remaining OEM cables
# Torque A46 stud nuts to 15 Nm (11 ft-lb)

Nothing else goes on these studs.

==== 1. Battery in tray ====
# Vent hose connected
# Hold-down installed
# Positive terminal FIRST
# Negative terminal LAST

==== With multimeter: ====

===== - Engine OFF: 12.5–12.8 V =====

===== - Should be within 0.05–0.1 V of battery =====

===== - Voltage should remain stable =====
* No immediate drop to 11’s

If this passes → the electrical foundation is fixed.

==== - Do not crank excessively ====
* It should start normally
* Idle should be stable
* No rapid clicking, no resets

After start:
* Charging voltage: 13.8–14.6 V

==== You removed: ====
* A melted distribution box
* A damaged lug
* A high-resistance main feed

That restores:
* DME power
* Fuel injection voltage
* Coil saturation
* CAS stability

This is the exact fix for fast-crank / no-start with low key-on voltage on E90s.

==== You didn’t just “replace a part.” ====
You corrected a primary power architecture failure.

Once this cable and A46 are done together, this problem does not come back.

===== - Exact OEM part number by VIN =====
* Starter & alternator post-repair checks
* ISTA battery registration (if needed)
* Cleaning up/removing the aftermarket wiring properly

You made the right call. Let’s finish it clean.