Crank but no start; potential short circuit?

[Samuraisaint]

BMW 320D M Sport 54

Greetings,

I am a novice, therefore I appreciate your patience.

When connecting the multimeter to the fuel pump connection (the white/blue wire and the brown wire), continuity is seen during a continuity test, whether the vehicle is entirely off or the ignition is on. This suggests the possibility of a short circuit.

Each component exhibits continuity when individually connected to the chassis, which I presume is standard.

Am I accurate in asserting that power and ground should not exhibit continuity? If this is not the case, has anybody encountered this issue and may provide guidance on further steps?

Thank you in advance.

[Grundysp]

Should I use the resistance setting instead of continuity? Attempt to measure whether there is 12 volts across the pump wires with the ignition activated.

[Mezuzzi]

Is the plug attached to the gasoline pump, or is it disconnected?

[Samuraisaint]

I have unplugged the plug and tested it; I do not see 12V on the positive wire when the ignition is activated. I have inspected fuse 3 and 54, and the relay has also been replaced. I get 5 volts in the next wire.

[Grundysp]

What is the power status at the relay? Is there a 12-volt supply, a proper ground connection, and 12 volts at the coil when the pump is activated?
I presume that an E46 from that period used a regular relay for the fuel pump instead of a module. I am not well-versed on the E46, since I have never worked on them.

[Samuraisaint]

I have not yet progressed to checking the power at the relay. I assume I can remove the relay to test the pins, or is there an other technique to do this?

[Istairde]

Uncertain if the pump primes with ignition. Operates alone when the ECU detects a signal from the crank sensor.

[rauman]

Your comprehension is accurate. In a well operating electrical system, the power wire (typically the coloured wire, in this instance, white/blue) and the ground wire (brown) must not exhibit continuity between them. Measuring continuity between these two wires may suggest a short circuit inside the wiring harness or a defect in the fuel pump itself.

Below are the further actions you may do to better identify the issue:

1. Examine the Wiring: Assess the wiring between the fuel pump connection and the fuel pump for indications of damage, including fraying, abrasion, or exposed wires that may be responsible for a short circuit.

2. Evaluate the Fuel Pump: If feasible, assess the fuel pump directly. An defective pump may exhibit internal shorting that might influence the continuity measurements.

3. Isolate the Circuit: Detach the fuel pump connection and re-evaluate the continuity between the power and ground wires at the connector. If continuity persists with the pump unplugged, the problem is probably inside the wire harness.

4. Inspect for Ground Faults: Verify that the ground connection to the chassis is clean and secure. A deficient ground connection may result in anomalous results.

5. Consult a Wiring Diagram: Refer to the wiring diagram pertinent to your unique BMW model to comprehend the intended configuration of the fuel pump circuit.

6. Examine Additional Components: If the wiring and pump are OK, investigate additional circuit components that may be causing a short circuit.

If you persist in experiencing difficulties or are uncertain about certain procedures, it may be prudent to seek the expertise of a professional mechanic who can do a comprehensive diagnostic assessment.

[Istairde]

Disregard continuity for the moment; the first step is to verify that the ECU is receiving a signal from the crank sensor.