Output speed sensor failure on Allison 1000 throws P0722, often locks limp mode. The fix is one of the easiest DIY jobs on the Duramax. 15 minutes, $50 part.
Symptoms of bad output speed sensor
Drive symptoms:
- Stuck in 4th or 5th gear (limp mode)
- Speedometer dead or erratic
- Cruise control stops working
- ABS warning sometimes
Codes:
- P0722 - output speed sensor no signal
- P0723 - output speed intermittent
- Sometimes P0500 (vehicle speed)
Where the sensor is
Location:
- Top of transfer case adapter
- Driver side of trans tailshaft
- Sometimes called VSS (vehicle speed sensor)
- Easy access from above or under truck
Look for:
- Single 10mm bolt holding bracket
- 2-pin electrical connector
- Small cylindrical sensor
Parts you need
Sensor:
- AC Delco 24225335 (OEM)
- $30-$80 part
- Same sensor 2001-2010 most years
O-ring:
- Comes with sensor usually
- Or order separately $5
- Do NOT reuse old O-ring
Optional - thermal grease:
- Helps connector seal
- Some dielectric grease
- $5
Tools needed
- 10mm socket
- Ratchet
- Extension
- Maybe a flashlight
- Small flat screwdriver (connector tab)
Step-by-step procedure
Step 1: Disconnect battery (optional but good)
- Negative cable off
- Protects PCM
Step 2: Locate sensor
- Crawl under driver side
- Look at top of transfer case / trans tail
- Follow electrical connector
Step 3: Disconnect electrical
- Press tab on connector
- Pull connector off
- Move wires aside
Step 4: Remove sensor
- 10mm bolt holds bracket
- Remove bolt
- Pull sensor out (small twist sometimes needed)
Step 5: Inspect
- Check for metal shavings on sensor tip
- Bad shavings = bigger problem (planetary wear)
- Light film of fluid normal
Step 6: Install new sensor
- New O-ring greased lightly
- Press sensor into bore
- Bracket on, 10mm bolt
- Torque to 8 ft-lb
Step 7: Reconnect electrical
- Connector clicks on
- Pull back to verify locked
- Reconnect battery
Step 8: Clear codes
- Scan tool to clear DTCs
- Drive cycle to verify fix
- 20+ miles to relearn
Total time and cost
DIY:
- Sensor: $30-$80
- Time: 15-30 minutes
- Tools you already own
- Total: $30-$80
Shop:
- Parts: $50-$100
- Labor: $80-$150
- Total: $130-$250
Dealer:
- Parts: $120-$200
- Labor: $150-$250
- Total: $270-$450
- Same sensor, marked up
Common mistakes
Reusing old O-ring:
Cross-threading bracket bolt:
Skipping code clear:
Verifying fix worked
Symptoms gone:
If code returns:
If sensor was not the cause:
While you have it apart
Optional checks:
Why not just go to the dealer?
Math:
Skill level:
When to NOT DIY
If:
Then:
Bottom line
Cheapest Duramax fix available:
Worth trying first:
Need Allison output speed sensor, internal sensor, or solenoid pack? Visit our Allison catalog. OEM sensors, full sensor kits, complete rebuild bundles. Free shipping over $70.
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