Speed Sensor (OBD2 Scanner) Fault Diagnosis
If you suspect your vehicle’s speed sensor is faulty, it’s important to get a proper diagnosis from a qualified mechanic (or yourself, if possible) before replacing any parts. While the symptoms above may indicate a faulty sensor, an entirely different issue could be causing the same symptoms. Here are some diagnostic methods you can use to identify the actual root cause:
1) Visual Inspection
Step one is to thoroughly inspect the speed sensor. The mechanic will check the sensor for visible damage, such as cracks, corrosion, or loose connections. They’ll also inspect the wiring harness for signs of wear, fraying, and even rodent damage (yes, it happens).
2) OBD2 Scanner
Nearly every vehicle on the road today is equipped with an on-board diagnostic (OBD) system that can detect and store fault codes for various components, such as the speed sensor. A diagnostic tool can be used to retrieve the stored codes and determine if they are related to a problem with the speed sensor. Common speed sensor codes include:
P0500 (Vehicle Speed Sensor Failure)
P0501 (Vehicle Speed Sensor Range/Performance)
P0715 (Input/Turbine Speed Sensor Circuit Failure)
P0720 (Output Speed Sensor Circuit Failure)
3) Multimeter Test
In some cases, a mechanic may use a multimeter to test the resistance and continuity of the speed sensor and its wiring. This method is especially useful when resolving passive sensor issues, such as: B. Sensors that change identification resistance. The readings can be compared to the manufacturer’s specifications to determine if the sensor is functioning properly.
4) Oscilloscope Test
An oscilloscope is a powerful diagnostic tool that allows a mechanic to visualize the waveforms produced by the speed sensor. By connecting an oscilloscope to the sensor wiring, the quality and consistency of the signal can be evaluated. A defective speed sensor may produce an erratic signal, a weak signal, or no signal, indicating that replacement is necessary.
5) Road Test
Finally, the auto technician may perform a road test to evaluate the vehicle’s operation and confirm the diagnosis. During the road test, they will monitor the speedometer, odometer, transmission shifting, and other systems affected by the speed sensor. This is often done using specialist diagnostic tools that read and record live data.
