Abnormal line impedance is the significant culprit in Fuel Pump damage. Tests show that when the resistance of the power supply wiring harness increases from the normal 0.5Ω to 2.3Ω, the terminal voltage of the fuel pump motor will drop from 13.5V to 10.8V (a drop of 20%), and the motor speed will reduce from 3000rpm to 2400rpm and the fuel supply pressure will fall from 4.5bar to 3.2bar, resulting in an air-fuel ratio deviation of ±15%. Tesla Model Y’s recall incident in 2023 revealed that the defect in the front compartment wiring harness design caused the Fuel Pump circuit contact resistance to change by ±0.8Ω, the armature current of the motor by 28% above the limit, the winding peak temperature by 145°C (exceeding the 120°C design limit), and the failure rate by 5.3 times.
Voltage spikes directly threaten the Fuel Pump’s life. In a case, the failure of the generator regulator caused the transient voltage to reach as high as 18V (33% over nominal), and the demagnetization rate of the permanent magnet of the Bosch 044 pump increased by 7 times. Its power output degraded from 120W to 75W in just 200 hours. SAE tests show that when the voltage fluctuation amplitude exceeds ±15%, the spark frequency between the brush and the commutator rises from 50 times per second to 120 times per second, and the carbon brush wear rate increases by 140%. Ford disclosed in 2022 that, due to the corrosion of the wiring harness terminals (contact area reduction by 60%), the operating current of the Fuel Pump increased from 5A to 8.2A, and the junction temperature of the MOSFET switch tube rose at a rate of 12°C/ minute, ultimately resulting in an 89% chance of burnout of the ECU fuel pump drive module.
Insulation deterioration leads to catastrophic failure. A case of a specific repair garage shows that the use of wires of non-flame-retardant grades (with a temperature resistance grade of 105°C rather than) The original plant changed the Fuel Pump circuit at 150° C. At the high-temperature environment of the engine compartment, the carbonization process of the insulation layer was accelerated three times, and the peak value of the inter-line short-circuit current was over 40A (the fuse rated value is 15A), which burned out the motor winding of the pump body directly. The data in the industry indicates that when the cross-sectional area of the conductor is reduced from 2.5mm² to 1.0mm², the voltage drop in the line increases by 2.8 times, causing the Fuel Pump to operate at 120% of the rated power, and the life of the bearing reduces significantly from 100,000 kilometers to 23,000 kilometers. BMW’s technical update confirmed that in the humid climate (humidity > 85%), when the waterproof level of the wiring harness is less than IP67, the pins of the connectors will be oxidized, and contact resistance will rise by 0.2Ω every month. The fuel flow error will be ±22% after six months.
Electromagnetic interference (EMI) leads to incorrect control. In a modification case, the exposed power wire of the Fuel Pump was run parallel to the CAN bus by 15cm, and it worsened the signal-to-noise ratio of the PWM control signal from 20dB to 6dB. There was an increase in the probability of the ECU misinterpreting the fuel demand by 43%, which resulted in a deviation of ±25% of the fuel supply pulse width. The testing on the ISO 11452-2 standard shows that when the radio frequency interference field strength is 50V/m, the bit error rate of the fuel pump control module rises from 0.01% to 1.2%, and it can lead to fuel supply interruption (with a frequency of up to 3 times per minute). In 2021, due to the high-voltage cable of Volkswagen ID.4’s excessive EMI radiation, the distortion rate of the Fuel Pump control signal on the low-voltage side was as high as 7%, forcing the vehicle failure rate to have the speed limited to 50km/h to increase by 12 times.
Improper wiring harness layout exacerbates mechanical damage. Toyota service records show that when the bending radius of the Fuel Pump cable is shorter than 50mm (when the standard requirement is 80mm), wire breakage is six times more likely. The owner of a Kia K5 paid a repair cost of ￥4,200 due to the absence of a wire harness fixing clip, and the wire scraped against the vehicle frame and the skin was damaged when the car vibrated (frequency: 8-15Hz). The short-circuit current corroded the fuse box. Ford F-150 wire harness tension test indicates that when the wire is under the action of continuous tension over 50N, the copper wire’s fatigue fracture cycle reduces from 10 years to 2.8 years, and the fuel pump power supply interruption risk rises by 17 times.
Compliant solutions can reduce risks: The use of a FLIR thermal imager to monitor the line’s rise in temperature (with an early warning if the temperature differential is more than 15°C), in combination with a micro-ohmmeter (±0.01Ω precision) for measuring contact resistance, can forestall 92% of Fuel Pump circuit failures in advance. The Mercedes-Benz ESS diagnostic system dictates that the voltage drop over the fuel pump circuit must be less than 0.3V (for a load current of 5A), otherwise the maintenance code U140800 will be triggered. Field experience has shown that wiring harnesses with gold-plated terminals (contact resistance < 0.1Ω) and silicone sheaths (temperature resistance -40°C to 200°C) can raise the MTBF (Mean Time between Failures) of the Fuel Pump system from 6,000 hours to 15,000 hours.
