The vehicle

• 2000 BMW E46 318i
• BMS46 Engine Control
• Engine Code M43TU

The problem

The vehicle had been driven through a flooded area, and water had entered the block via the air intake. The car cut out with the engine flooded with water. The cold water entered the hot cylinder block, and caused it to crack due to thermal shock. The engine had been replaced, but could not be started. The vehicle was towed to our garage, but we soon discovered that no diagnostic scan could be performed due to no communication to the modules.

The investigation

After a thorough investigation of the relevant fuses, checking supply voltages, ground (earth) signals, immobilizer signals, and the primary ignition voltage, we discovered that:

• The primary ignition was being supplied with 12 V, but the ECU was not triggering the coils, which resulted in no spark being produced.
• The relevant fuses were intact.
• The immobilizer signal was available as soon as the ignition key was turned and therefore was not at fault (see Figure 1).
• The Crankshaft Sensor did not deliver a valid signal. The power supply for the sensor was only 500 mV once the car was started. (see Figures 2 and 3).

Figure 1: A good signal from the immobiliser to the ECU

Figure 2: Blue = Crank shaft sensor, Red = Hall sensor supply (should be 12 V)

Figure 3: The crank shaft signals zoomed

The solution

We checked the wiring of the crank shaft sensor and could not find any faults. The sensor itself had been replaced by the client already. We did notice that without the sensor connected - there was no sufficient power supply to the sensor from the ECU. This led us to believe the ECU must be faulty.

The result

We opened the ECU and found the proof. The power connector was destroyed by extreme overload (see Figure 4). We were confused as to why the fuses did not trip to protect the ECU.

Figure 4: ECU with damanged power connector

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