Powertrain, generic · Transmission

P0721 Output Shaft Speed Sensor Circuit Range/Performance

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modePossible

The output shaft speed sensor (Hall or inductive) reports the speed of the transmission output; it gives the gear ratio together with input speed and on many vehicles also the road speed for speedometer and cruise control. P0721 means the output speed is present but implausible: too high (Ford 6R80 above 7450 rpm), not matching wheel or input speed in the engaged gear (ZF 6HP26 more than 200 or 250 rpm apart, Ford's F21 more than 15 % for 10 s), or jumping (Allison 1000: 500 rpm within 0.15 s). On GM's 10-speed with a direction-sensing sensor, P0721 means the reported direction of rotation does not fit – since 2025 after two trips, earlier after one. Wrong tyre sizes or a faulty wheel speed sensor can also falsify the comparison.

Likely causes

Output speed sensor faulty or dirty (metal debris)
Contact problems or interference in the sensor circuit
Wrong tyre size or axle ratio, faulty wheel speed sensor
Reluctor wheel damaged or sensor mounted wrongly

Symptoms

  • Speedometer jumps
  • Warning lamp
  • Wrong shifts, limp mode
  • ABS/ESP warning possible if wheel speed is affected

Repair estimate

DifficultyMediumDIY possible
Parts and labour€80–450
Time0.5–2.5 h

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

output speed sensorsensor wiringtransmission control module

Related codes

P0720P0722P0723P0716P0500

References: newtonnet.co.uk, gsi.ext.gm.com, gsi.ext.gm.com, gsi.ext.gm.com.