The abnormal opening and closing of the electronic throttle (ETC) is often implicitly associated with the Fuel supply fluctuations of the Fuel Pump. When the oil pressure fluctuation exceeds ±15% of the rated value (for example, the standard value drops from 350kPa to 297kPa), the engine control module (ECU) is forced to increase the throttle opening Angle by 8 degrees within 0.5 seconds to compensate for the thinning of the mixture. The 2023 SAE research report confirmed that such high-frequency corrections cause the variance value of the throttle position sensor (TPS) voltage signal to surge from the normal 0.02V to 0.15V, increasing the probability of triggering the fault code P0121 by 6.7 times. Specifically, when traveling at a constant speed of 30km/h, the pedal opening remains constant but the vehicle speed fluctuates by ±7km/h.
The decline in the flow rate of Fuel Pump forces ETC to enter the unauthorized control mode. Measured data shows that when the volumetric efficiency of the pump body is lower than 78% and the idle fuel flow rate is less than 40L/h (the calibration requires 60L/h), the ECU automatically expands the default throttle opening from 3% to 6.5%, causing the stress load on the reset spring plate to increase by 42%. The technical notice of BMW G20 shows that under this condition, the wear rate of the throttle shaft sleeve reaches 0.1mm per 10,000 kilometers (normal value 0.03mm), and after 80,000 kilometers, the opening deviation exceeds ±2.7%, causing the idle speed to fluctuate periodically between 700 and 950rpm, and the perceived vibration frequency of passengers increases to 14 times per minute.
Fuel pressure oscillation causes the throttle anti-jamming lock. The ETC system of modern models is equipped with a collision protection mechanism. When an unexpected opening change is detected to be greater than 15°/ second (less than 8°/ second under normal operation), the system enters an emergency state. Bosch laboratory verification: When the filter screen of an aging fuel pump is blocked by 38%, the sudden drop in oil pressure during rapid acceleration causes the ECU to misjudge the “logic conflict of the accelerator pedal”, triggering the throttle valve to be forced half-open (the opening degree is locked at 45%). In the 2022 Toyota Camry recall incident, 12% of the faulty vehicles suddenly encountered power limitations while cruising at 70km/h. The fundamental cause was a sudden drop in fuel pressure, which triggered the activation of the ETC safety protocol.
The electrical interference of the Fuel Pump is conducted to the sensor system. The wear of the motor brushes (carbon brush thickness < 1.5mm) causes the current harmonic distortion rate to exceed 18%, generating electromagnetic interference in the 1200-5000Hz frequency band. The Lexus diagnostic manual records that this interference causes the peak-to-peak noise of the TPS signal to reach 0.3V (the allowable value is 0.05V), increasing the delay in the ECU’s recognition of the actual position of the throttle to 35 milliseconds (the standard is 10 milliseconds). In the Mercedes-Benz M274 engine, this causes the valve response time to be delayed from 0.22 seconds to 0.37 seconds during rapid acceleration, and the overtaking time from 80 to 120km/h increases by 1.9 seconds.
The system solution requires hierarchical diagnosis:
First, measure the idle oil pressure (for example, for the Volkswagen EA888, it needs to be ≥4.0bar, with a deviation of less than ±0.2bar)
Observe the closed-loop correction frequency of the ETC Angle (health value < 5 times per minute)
Collect the slope of the oil pressure curve during the acceleration process (greater than 300kPa/ second is considered qualified).
According to statistics from Subaru’s technical Center, among the cases of throttle related maintenance indirectly caused by Fuel Pump malfunctions, 71% of the abnormalities disappeared after the fuel pump was replaced. A typical manifestation is that for Forester models with a mileage of over 100,000 kilometers, after the fuel supply system was repaired, the frequency of throttle reset learning dropped from an average of 3.1 times per month to 0.2 times. This not only reduces the average maintenance cost of the throttle body by ¥1,600, but also restores the throttle body’s lifespan to the designed value of 120,000 kilometers, avoiding a 92% risk of throttle body jamming.