Abnormal fuel pressure is the most direct sign. Under normal operating conditions, the fuel rail pressure should be maintained at 280-350bar (for direct injection systems). When the built-in motor winding is short-circuited, the output pressure drops sharply below 60bar. The actual measurement data of a certain German car shows that when the pressure fluctuation amplitude exceeds ±15bar for more than 5 seconds, there is a 98% probability of rotor open circuit, and at this time, the fuel flow gap in the acceleration condition reaches 22%.
Current waveform distortion indicates insulation failure. The working current of A healthy Fuel Pump should be stable at 6.5±0.8A (for a 12V system). If a current spike greater than 12A is detected and persists for 200ms (exceeding the fuse melting time), it indicates that there is a ring fire in the carbon brush commutator. BMW repair cases show that such faults cause the armature temperature to instantly exceed 420℃, far exceeding the 180℃ limit of H-class insulation.
The abnormal noise frequency band can locate the fault point. When the ball bearing cage breaks, the vibration accelerometer measures that the amplitude increases to 5.8m/s² in the 2000Hz frequency band (standard value ≤0.4m/s²). Acoustic analysis confirmed that the energy proportion in the 40kHz ultrasonic frequency band exceeded 15% (less than 3% for new vehicles), often accompanied by the “clattering” sound of cage fragments rubbing against the stator slots.
The sharp increase in power loss exposed mechanical damage. When the oil pump motor of the Nissan Sylphy Hybrid had a short circuit between winding turns, the input power soared from 110W to 290W, and the efficiency dropped from 85% to 31%. The thermal imager shows that the hot spot temperature of the coil reaches 156℃, far exceeding the upper limit of 130℃ for B-class insulation, causing the epoxy resin to carbonize and release a burnt smell.
The hysteresis of the speed response reflects the attenuation of torque. The test requirements for Cummins ISX engines are as follows: from idle to full throttle, the fuel pressure needs to rise to 310bar within 0.8 seconds. If the response time exceeds 1.5 seconds and is accompanied by a humming sound from the motor, it indicates that the permanent magnet has demagnetized, resulting in a speed loss rate of ≥35% and a torque output less than 60% of the rated value.
Cases of medium intrusion caused by seal failure are not uncommon. After the pump shaft seal of Ford’s 1.5T Ecoboost was broken, gasoline seeped into the motor cavity to form an explosive mixture. Resistance tests showed that the resistance value of the winding to ground suddenly dropped from 10MΩ to 1.2kΩ. The short-circuit current eroded the commutator, forming a 3mm diameter pit. This defect led to the recall of 137,000 vehicles in North America in 2019.
Preventive diagnostic strategies can avoid risks. It is recommended to test three parameters every 60,000 kilometers: current ripple coefficient (> 15% requires warning), DC resistance imbalance rate (> 3% abnormal), and pressure establishment time (20% deviation from the benchmark indicates failure). The verification of the Bosch FSA system shows that the prediction accuracy rate of this method reaches 91%, avoiding a single maintenance loss of ￥8,200.