DF031 OBD2 reports a sensor fault, replacement of the sensor is unlikely to resolve the underlying problem. The fault is most likely to be caused by the systems that the sensor is monitoring, but might even be caused by the wiring to the sensor itself.
OBD 2 DF031 code and tailpipe testing are two different approaches to identify vehicles in need of repair. The OBD system looks for broken or malfunctioning emissions control components while tailpipe tests sample a vehicle's exhaust to see if it is above or below certain prescribed limits. Given the robust nature of today's emissions control components, it is entirely possible for an individual component to malfunction without leading to an immediate increase in emissions at the tailpipe. In such cases, other components (like the catalyst) can temporarily compensate for the part that is broken however, these other components can only do double duty for so long before they, too, begin to malfunction. Because of its ability to monitor individual components, OBD is able to give motorists an early warning that repairs are needed; it is because of this early warning capability that OBD will sometimes fail vehicles that would otherwise pass a tailpipe test.
Remove the air filter box assembly so you can access the transmission range switch. Turn the key to the ON position, but do not start the vehicle. Move the shifter to the neutral position. Align the alignment holes between the switch and the shift lever. Insert a 5mm drill bit into the adjustment hole to verify the proper alignment for the neutral position.
Vehicle Speed Sensor (VSS) Out of Self Test Range Indicates the VSS input signal is out of Self Test range. If the PCM detects a VSS input signal any time during Self Test, a DTC P1501 will be set and the test will abort. Noisy VSS input signal from Radio Frequency Interference/ Electro-Magnetic Interference (RFI/EMI) external sources such as ignition wires, charging circuit or after market equipment. Check for VSS input to be 0 mph when vehicle transmission is in Park.
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