What Causes the Audi to Report Sensor Reference Voltage A Too Low?
2 Answers
Audi reports sensor reference voltage A too low because the voltage is 5.03V, and the voltage at T6L/2 is 39V. Similarly, measurements of each wire from the accelerator pedal to the engine control module show normal conductivity, with no grounding or power short-circuiting. Below are the specific causes and solutions: Specific Causes: The P064200 fault symptom is that the engine fails to start. Sensor reference voltage A not only supplies power to the throttle angle sensor and accelerator pedal position sensor 1 but also to the engine speed sensor G28, intake camshaft position sensor G40, fuel rail pressure sensor G247, boost pressure sensor G31, and intake temperature sensor G299. Solutions: Measure the power supply to G28/G40/G247/G31/G299 separately, all at 5.03V. Disconnect all the above sensor connectors, and the power supply to the throttle and accelerator pedal position sensor 1 remains at 0.29V.
The Audi reports a sensor reference voltage A too low, which is usually a sign of an electrical system fault. From my experience, possible causes include internal sensor damage leading to leakage, short circuits or breaks in the power supply line affecting voltage stability. It could also be due to low battery voltage or insufficient alternator output, commonly seen in older models or vehicles under prolonged high-load driving. Oxidation and corrosion at grounding points can also increase resistance, dragging down the reference voltage. For diagnosis, start by using an OBD device to read the specific fault code, then systematically check for loose sensor connectors and test input and output voltage values. Ignoring this issue may lead to reduced engine performance or the sensor falsely reporting other errors. I recommend visiting a professional repair shop for a comprehensive inspection to avoid the risks of DIY repairs.
