Symptom: a modern Sonata car equipped with 4-cylinder electronic fuel injection engine, there has been idle instability, high and low speed, and in the low-speed driving, the occasional channeling phenomenon. When the fault occurs, the CHECK warning light on the dashboard is illuminated.
    Troubleshooting: CHECK warning light on the dashboard light, indicating that the electronic control system is faulty, call the fault code, shown as "14", which means that the throttle position sensor signal is not normal. Remove the harness position sensor on the harness connector, observe the terminals and found no rust, contact is also reliable. Refer to the service manual to measure the resistance of the throttle position sensor with a multimeter. When the hand-operated throttle is fully transited from full clearance, it is found that the resistance value does not change linearly, but the resistance value is abrupt when the clearance (slight vibration) and the opening are not large. This shows that the throttle sensor within the sliding resistance of the phenomenon of poor contact. Replace the new throttle position sensor, remove the fault code, troubleshooting.
    Failure analysis: the engine's throttle position sensor from idle to high-speed smooth transition, the input resistance to the computer should be 0.5kΩ smooth rise to 3.5 ~ 6.5kΩ. The above fault is due to the sudden change in the output resistance value at the idling (slightly vibrating) or low speed of the throttle position sensor, resulting in an incorrect signal input to the computer (equivalent to a sudden opening or reduction of the throttle opening) There is a phenomenon of abnormal engine work.