P0721Powertrain
Powertrain · SAE
Output Speed Sensor Circuit Range/Performance
Meaning
The output shaft speed sensor signal is present but erratic or inconsistent with the expected value relative to vehicle speed or other operating parameters. The TCM detects an incoherence in the signal that prevents its reliable use for transmission management.
Common causes
- Damaged output shaft reluctor ring with broken or missing teeth
- Excessive air gap between sensor and reluctor ring
- Intermittent connection at the sensor connector or wiring harness
- Sensor partially contaminated by metallic particles or debris
- Internal sensor fault producing an unstable signal
Symptoms
- Malfunction indicator lamp (MIL) illuminated, sometimes intermittently
- Erratic or unreliable speedometer reading
- Irregular or ill-timed gear shifts
- Improper ABS or stability control system interventions
- Transmission cycling between normal and limp mode
Severity
Medium to high severity: the unreliable signal degrades shift quality and can cause malfunctions in active safety systems that depend on vehicle speed data.
What to do
- Read fault codes and monitor output speed live data during a road test
- Inspect the reluctor ring for damage, broken, or missing teeth
- Check the air gap between sensor and reluctor ring against specifications
- Inspect the sensor connector and wiring harness for intermittent contacts or corrosion
- Clean the sensor of metallic deposits and retest operation