Poor grounding directly causes an abnormal increase in the current path impedance. When the loop resistance exceeds 50 milliohms (the standard requirement is ≤20 milliohms), the spark discharge energy of the Fuel Pump brush surges by 300%, carbonizing the commutator copper sheet at an average annual rate of 0.15 millimeters. Chrysler’s technical notice confirmed that the grounding points of the 2018-2020 model of the lambskin caine frame were rusted (measured resistance 380 milliohms), the peak-to-peak fluctuation of the working current reached ±4.2A (standard ±0.8A), the winding temperature rose to 172℃ (threshold 85℃), and the probability of interlayer short circuit increased by 22 times. Recall data shows that this defect has sharply reduced the average lifespan of the oil pump from 120,000 kilometers to 34,000 kilometers, and the corresponding maintenance cost has increased by 320 US dollars per unit.
The voltage fluctuation caused by poor grounding interferes with the stability of the control system. When the loop resistance is greater than 100 milliohms, the signal-to-noise ratio of the PWM signal deteriorates from 60dB to 38dB. Experiments on the Volkswagen MQB platform show that grounding anomalies cause a 15-millisecond delay in the ECU duty cycle command, and the fluctuation range of the oil pump speed expands to ±18% (standard ±3%). More seriously, in 2021, the BMW X5 stall due to poor grounding of the brake light, generating a 0.3V reverse electromotive force, which triggered the Fuel Pump controller to misjudge the overcurrent protection. Such accidents accounted for 72% of the total faults. According to statistics from the North American Highway Safety Administration (NHTSA), 29% of abnormal oil pump damages in the past five years can be traced back to grounding defects.
Electrochemical corrosion and mechanical vibration form a fatal combination. In the salt spray environment of coastal areas, the annual corrosion rate of grounding sheets reaches 0.1g/m². The maintenance report of Ford F-150 reveals that the ground resistance of the vehicle that has been in use for five years has risen to 1.2Ω, resulting in:
The peak voltage dropped to 9.3V (rated 13.5V).
The armature torque decays by 41%
The proportion of dry friction time of the bearing exceeds 30%
Multiple stresses cause the probability of ceramic brush breakage to reach 67%, and such faults account for 89% in vehicles with a mileage of over 100,000 kilometers. Chevrolet dealer data indicates that the radial runout of the impeller shaft caused by this exceeds 0.1mm (allowable value 0.03mm), and the fuel flow rate has decreased by 27%.
The prevention and control strategies need to adopt systems engineering methods. The German Volkswagen TL82445 standard stipulates that the full grounding resistance must be controlled within 20 milliohms (the actual measurement should use a microohm meter with an accuracy of ±0.5%). Volvo’s solutions include:
Zinc-nickel alloy coating with a conductivity of 98% (thickness ≥15μm)
Adopt a three-bolt star grounding structure (with the contact area expanded by 230%)
Integrated real-time resistance monitoring circuit (accuracy ±2 milliohms)
Actual verification shows that this scheme reduces the grounding failure rate from the industry average of 0.47 times per year to 0.02 times per year. The data from Chevrolet 4S stores further confirm that the AWG10 wire diameter upgrade and laser cleaning of the contact surface (at a cost of $45 per vehicle) can reduce the electrical failure of the Fuel Pump by 83%, save 41% of the maintenance cost throughout the entire life cycle, and at the same time avoid the risk of traffic accidents caused by fuel supply interruption (with a probability reduction of 92%). These pieces of evidence fully prove that the grounding quality is the core variable of the reliability of fuel pumps.