Error code P0721 is displayed and the check engine light is on - what does this mean?
The OBD system detects an error in the transmission's output speed sensor, which sends an implausible or missing signal to the control unit. This DTC P0721 affects the automatic transmission and can occur in various manufacturers such as Ford, GM, Chrysler and others, although the specific symptoms may vary slightly.
What can cause this fault code?
- Defective output speed sensor of the transmission
- Damaged wiring to the speed sensor
- Corroded or loose plug connections
- Defective transmission control unit (TCM)
- Mechanical problems in the transmission
- Dirty or damaged sensor ring
- Short circuit in the sensor circuit
- Defective ground connection
What symptoms occur in parallel with fault code P0721?
- Shifting problems: The automatic transmission shifts irregularly or jerkily
- Emergency running program: The transmission switches to safety mode with limited gears
- Speedometer failure: The speedometer does not work or displays incorrect values
- ABS problems: The anti-lock braking system may be affected
- Poor fuel efficiency: Increased fuel consumption due to suboptimal shift points
- Starting problems: The vehicle may not shift out of park
How can the problem of error code P0721 be rectified?
- The repair requires a systematic approach to identify the exact cause.
- Replace the output speed sensor: Locate the defective sensor on the transmission housing, remove old seal, install new sensor with correct torque and ensure plug connection
- Repair wiring: Identify damaged wiring between sensor and control unit, replace defective sections with new wiring and insulate all connections
- Clean plug connections: Remove corrosion from contacts, apply contact spray and plug connections firmly together, ensuring correct latching
- Replace the transmission control unit: Replace defective TCM with new or overhauled control unit and then have it programmed
- Clean or replace sensor ring: Clean dirty ring at transmission output or replace with new ring if damaged
- Check ground connections: Clean and tighten all ground connections on the transmission and replace if corroded
FAQ - Frequently asked questions about DTC P0721
Can I continue driving with error code P0721?
Short distances are possible, but you should have the problem rectified quickly. The transmission may switch to emergency mode, which can significantly reduce driving performance and lead to further damage.
How much does it cost to repair error code P0721?
The costs vary depending on the cause: a new output speed sensor costs 50-150 euros, wiring repairs 100-300 euros, while a transmission control unit can cost 500-1500 euros. The working time is usually 1-3 hours.
How can I diagnose fault code P0721 myself?
You can read out the code using an OBD scanner. First check the plug connections on the sensor and check the wiring for visible damage. A multimeter helps to measure the voltage at the sensor.
Does error code P0721 occur more frequently under certain driving conditions?
Yes, the error often occurs when driving on the highway or when accelerating, as the speed differences between the input and output of the transmission are greatest here and sensor errors become more obvious.
Can error code P0721 affect other systems?
Yes, as the output speed sensor also supplies data for ABS, ESP and the speedometer, these systems can also be affected. Additional error codes often occur in these areas.
How do I prevent error code P0721 from occurring again?
Regular transmission oil changes, protection from moisture and dirt and careful driving in puddles can help. Have the transmission checked for leaks during maintenance.
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