The 6L80 output shaft speed sensor (OSS) feeds vehicle speed to the TCM. Bad sensor = no shifts, no speedometer, limp mode. Simple to fix once you find it.
Symptoms of bad OSS
- P0722 (Output speed sensor no signal)
- P0723 (Output speed sensor intermittent)
- Speedometer reads zero while driving
- Cruise control inoperative
- Transmission stuck in 3rd gear (limp mode)
- Harsh shifts (TCM lost speed reference)
OSS location
- Mounted on driver-side rear of trans housing
- Visible from underneath
- 2-wire connector
- Hall-effect sensor over a reluctor wheel on output shaft
Diagnosis
Step 1: Pull codes
- P0722 confirms no signal from OSS
- P0721 suggests range/performance problem
Step 2: Resistance check
- Disconnect sensor
- Ohm across terminals: 800-1500 ohms = good
- Open or short = replace
Step 3: Signal check
- Backprobe sensor wires while driving
- Should see AC voltage proportional to speed
- No signal = sensor or wiring
Step 4: Inspect reluctor
- Pull sensor
- Look at reluctor wheel teeth through hole
- Damaged teeth = output shaft must come out
Replacement parts
OEM sensor:
- AC Delco 24251530
- $30-$60 part
- Direct replacement
Wiring connector pigtail:
- If connector pins are corroded
- $15-$30
Install
- Disconnect electrical connector
- Remove 10mm bolt holding sensor
- Pull sensor straight out
- Install new with new O-ring
- Torque to 10 ft-lb
- Reconnect electrical
- Clear codes with scan tool
Time and cost
DIY:
- Sensor: $30-$60
- Time: 30 minutes
- Scan tool to clear codes (or drive until light goes off)
- Total: $30-$60
Shop:
- Parts: $30-$60
- Labor: $100-$200
- Total: $130-$260
When sensor is not the fix
- Damaged reluctor wheel on output shaft (requires trans teardown)
- Wiring chafe between sensor and TCM
- TCM driver fault (rare)
Why this fails
- Heat from exhaust nearby
- Water intrusion at connector
- Vibration breaks sensor solder joints
- Typical failure: 80k-150k miles
Pair with TCM rebuild if older truck
- 2007-2010 6L80 TCMs prone to failure
- Check TCM ground integrity
- Read our 6L80 solenoid pack
Need 6L80 output speed sensor, wiring connector, or rebuild parts? Shop our 6L80 catalog. OEM sensors, wiring pigtails, complete rebuild kits. Free shipping over $70.
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