Technical Description of OBD-II Trouble Code
Range/Performance Issue with Output Speed Sensor
What does that signify?
This is a generic diagnostic trouble code (DTC) for powertrain and is applicable to OBD-II vehicles. This includes vehicles from various manufacturers such as VW, BMW, Mercedes, Chevrolet, GMC, Allison, Duramax, Dodge, Ram, Ford, Honda, Hyundai, Audi, etc. Although it is a generic code, the repair steps may vary depending on the 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 in the Output Speed Sensor Circuit, it can trigger a wide range of codes depending on the specific vehicle and automatic transmission.
Some common code responses related to Transmission Output Speed Sensor issues include codes P0720, P0721, P0722, and P0723. These codes indicate 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 a signal that indicates the speed of the transmission output shaft rotation. The PCM uses this information to control the shift solenoids, which direct fluid between hydraulic circuits and change the transmission gear ratio at the appropriate time. Depending on the vehicle and transmission configuration, the Output Speed Sensor may also control the speedometer reading. The Transmission Output Speed Sensor is a crucial component in the operation of an automatic transmission, as it controls the shifting of gears by ensuring fluid pressure is in the right place at the right time.
Code P0721 is set by the PCM when the Output Speed Sensor is out of range or not functioning properly.
What is the severity of this DTC?
The severity of this code typically starts as moderate, but if not corrected promptly, it can escalate to a more severe level.
Photo of a transmission speed sensor:
What are some of the symptoms of the code?
Symptoms of a P0721 trouble code may include:
What are some of the common causes of the code?
Possible causes for this P0721 transmission code include:
What are some P0721 troubleshooting steps?
Prior to starting the troubleshooting process for any malfunction, it is recommended to research the Technical Service Bulletins (TSB’s) specific to the vehicle’s year, model, and transmission. This can save a significant amount of time by providing guidance in the right direction.
The first step is to ensure the fluid level is correct and inspect the condition of the fluid for any contamination. It is also important to check the vehicle records to determine when the filter and fluid were last changed, if possible. Next, perform a thorough visual inspection of the associated wiring for any obvious defects such as scraping, rubbing, bare wires, or burn spots. Check the connectors and connections for security, corrosion, and damaged pins. This includes all wiring and connectors related to the output speed sensor, transmission solenoids, transmission pump, and the PCM. Depending on the configuration, inspect the transmission linkage for security and freedom of movement.
Advanced Steps
The advanced steps are highly specific to the vehicle and require advanced equipment to be performed accurately. These procedures involve using a digital multimeter and referencing the specific technical information for the vehicle. It is important to follow the troubleshooting guidelines and sequence specific to the vehicle. Voltage requirements may vary based on the vehicle model and transmission configuration.
Continuity Checks
Continuity checks should always be performed with the power removed from the circuit to avoid shorting the circuit and causing further damage. Unless otherwise specified by the technical data, the normal readings for wiring and connections should be 0 ohms of resistance. Resistance or lack of continuity indicates faulty wiring that is either open or shorted and must be repaired or replaced.
Common Repairs
Common Misdiagnosis
We always recommend seeking professional service to address this issue. However, if for some reason that is not possible, we offer the option to permanently delete this specific DTC. All other codes will continue to function. If you are interested in this option, please upload your ECU file to our portal.
