P0721 Output Speed Sensor Range/Performance
Description and meaning of DTC p0721
This is a generic powertrain diagnostic trouble code (DTC) and applies to OBD-II vehicles. That may include but is not limited to vehicles from VW, BMW, Mercedes, Chevrolet, GMC, Allison, Duramax, Dodge, Ram, Ford, Honda, Hyundai, Audi, etc. Although generic, the exact repair steps may vary depending on year, make, model and powertrain configuration. The P0721 OBD-II trouble code is associated with the Transmission Output Speed Sensor. When the Powertrain Control Module (PCM) detects a malfunction within the Output Speed Sensor Circuit a wide variety of codes can be triggered depending on the specific vehicle and the specific automatic transmission. Some of the more common code responses associated with Transmission Output Speed Sensor issues are codes P0720, P0721, P0722 and P0723 based on the specific malfunction that alerts the PCM to set the code and activate the Check Engine Light. The purpose of the Transmission Output Speed Sensor is to provide the PCM with signal that indicates the speed of the transmission output shaft rotation. The PCM uses these readings to control the shift solenoids. The solenoids direct fluid between various hydraulic circuits and change the transmission gear ratio at the appropriate time. Based on the vehicle and the transmission configuration the Output Speed Sensor may also control the speedometer reading. An automatic transmission is controlled by bands and clutches that change gears by having fluid pressure in the right place at the right time. This process starts with the Transmission Output Speed Sensor. Code P0721 is set by the PCM when the Output Speed Sensor is out of range or not functioning properly.
p0721 diagnostic trouble code symptoms
Symptoms of a P0721 trouble code may include: Poor fuel economyCheck Engine Light illuminatedTransmission does not shiftTransmission Shifts roughlyPossibly misfire-like symptomsPCM puts the engine into limp modeSpeedometer shows incorrect or erratic reading
DTC p0721 - possible causes
Causes for this P0721 transmission code may include: Defective Output Speed SensorDirty or contaminated fluidDirty or clogged transmission filterDefective Coolant Temperature SensorDefective Transmission Valve BodyRestricted hydraulic passagesFaulty Shift SolenoidCorroded or damaged connectorFaulty or damaged wiringFaulty PCM
How to fix OBD-II diagnostic trouble code p0721
Prior to beginning the troubleshooting process for any malfunction you should research the Technical Service Bulletins (TSB's) for the specific vehicle by year, model and transmission. In some situations this can save a lot of time in the long run by pointing you in the right direction. The first step is to make sure the fluid level is correct and inspect the condition of the fluid for contamination. You should also check the vehicle records to verify the last time that the filter and fluid was changed if possible. A thorough visual inspection to check the associated wiring for obvious defects such as scraping, rubbing, bare wires, or burn spots is next. Check the connectors and connections for security, corrosion and damaged pins. This should include all wiring and connectors to the output speed sensor, transmission solenoids, transmission pump and the PCM. Depending on the configuration, the transmission linkage should be inspected for security and freedom of movement. Advanced StepsThe advanced steps become very vehicle specific and require the appropriate advanced equipment to perform correctly. These procedures require a digital multi meter and the specific technical references for the vehicle. You should follow the specific troubleshooting guidelines and sequence for your vehicle. Voltage requirements may very based on the specific model of the vehicle and the transmission configuration. Continuity ChecksContinuity checks are always performed with the power removed from the circuit to avoid shorting the circuit and creating more damage. Unless otherwise specified by the technical data, the normal readings for wiring and connections should be 0 ohms of resistance. Resistance or no continuity is an indication of faulty wiring that is open or shorted and must be repaired or replaced.