P0721

Schematic:

The Vehicle Speed Sensor (VSS) produces an AC voltage of different amplitude and frequency depending on the velocity of the output shaft. The VSS produces the signal from 16 evenly spaced machined notches on the transaxle differential carrier. The vehicle speed sensor produces a readable AC voltage signal when vehicle speed is above 5 km/h (3 mph). This VSS signal is sent to the PCM, which is used to determine output shaft RPM. Missing or extra pulses in a revolution of the output shaft will be interpreted as noise by the PCM. Noise may be caused by an intermittent open, short to ground, or short to voltage. The level of noise is based on engine and output shaft speed. DTC P0721 sets when the VSS signal voltage at the PCM changes too rapidly indicating a noisy signal.

DTC PARAMETERS
DTC P0721 will set if the PCM has detected VSS signal noise when:
^ Speed noise parameter = YES
^ Condition exists for longer than 0.8 seconds
^ Condition exists twice in one ignition cycle
^ Vehicle speed is greater than 24 km/h (15 mph)

DTC P0721 diagnostic runs continuously when vehicle speed is greater than 24 km/h (15 mph).

DTC P0721 is a type A DTC

DIAGNOSTIC AIDS
Use Scan tool to monitor SPEED NOISE while driving vehicle. SPEED NOISE will = YES if noisy or missing VSS pulses are being received.

DTC P0721 can set due to an:
^ Intermittent open anywhere in the VSS circuit
^ Intermittent short to ground or short to voltage on circuit 401
^ Loose sensor
^ Electromagnetic Interference (EMI) caused by high current carrying wiring routed near the VSS sensor wiring. EMI can alter the amplitude and/or frequency of the VSS signal and create invalid VSS pulses.

An intermittent open anywhere in the VSS circuit or intermittent short to ground/short to voltage on circuit 401 will cause the VEHICLE SPEED parameter on Scan tool to momentarily drop out.