P0721 critical

Output Speed Sensor Circuit Range/Performance

The P0721 code means the vehicle's onboard diagnostic system has detected: Output Speed Sensor Circuit Range/Performance. This is a critical severity code.

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Keep driving?
Short distances only
DIY difficulty
hard
Estimated cost
$100 - $350 (parts and labor)
Check Your Fluid First
ANCEL AD310 OBD-II Scanner

Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.

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Common Symptoms

  • Check Engine Light illuminated
  • Speedometer reads incorrectly
  • Harsh or delayed shifting
  • Transmission slipping

Probable Causes (Ranked by Likelihood)

  • Faulty output speed sensor Very High
  • Damaged output speed sensor reluctor ring High
  • Contaminated fluid with metal debris near sensor Moderate
  • TCM output speed circuit fault Low

Step-by-Step Diagnostic Procedure

  1. Monitor output speed sensor on a scan tool while driving -- should increase smoothly with vehicle speed

  2. Compare output speed reading to GPS speed for accuracy

  3. Check transmission fluid for metal particles

  4. Inspect sensor connector and wiring for damage

  5. Replace the output speed sensor if readings are erratic

Frequently Asked Questions

Can I drive with code P0721?

Drive short distances only. Output Speed Sensor Circuit Range/Performance can cause unsafe or unpredictable transmission behavior.

What causes P0721?

The most common cause is a faulty sensor or wiring issue. Faulty output speed sensor is the most likely cause.

Is P0721 expensive to fix?

Typical repair costs range from $100 - $350 (parts and labor). Sensor replacement is the most common fix.

Sources

This page is built from documented references. Verify against your own service info before repair work.

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