Description
Paccar Q21-6005 speed/tachometer sensor for 1995-2011 Kenworth and Peterbilt trucks equipped with Eaton transmissions using an internal tone ring. The 2-pin rectangular sensor mounts in the transmission tailshaft housing on a 3/4-16 fitting and supplies the vehicle-speed and tachometer signals to the speedometer cluster, cruise control, and ECM. Common replacement when the speedometer drops to zero, the cruise won’t hold, or the ECM logs a vehicle-speed-input fault.
Signs You Need a New Speed Sensor
- Speedometer reads zero or fluctuates erratically while the truck is moving
- Tachometer fails to register engine RPM accurately
- Cruise control will not engage or drops out at highway speed
- Erratic transmission shift behavior tied to incorrect vehicle-speed signal
Specifications
| Manufacturer | Paccar (OEM) |
|---|---|
| Part Number | Q21-6005 |
| Part Type | Speed / Tachometer Sensor |
| Connector | 2-pin rectangular |
| Thread Size | 3/4-16 |
| Overall Length | ~3.70 in |
| Transmission | Eaton with internal tone ring |
Cross References
This part replaces or is equivalent to the following part numbers:
- Paccar / Kenworth / Peterbilt: Q21-6005, Q216005
- Peterbilt (Rig Tough): Q21-6005RT
- Automann: 577.75500
- Dorman: 505-5406 (supersedes 505-5405)
- Fortpro: F238839
Applications
This speed sensor fits the transmission tailshaft housing on the following Paccar trucks:
- Kenworth C500, K-series, T300/T400, T600, T660, T800, W900 (1995-2010)
- Peterbilt 357, 359, 362, 365, 367, 377, 378, 379, 384, 386, 388, 389 (1995-2011)
For Navistar / International applications using a 2-pin oval 3/4-16 sensor, see the related PAI 450599 speedometer sensor; for Freightliner, see PAI 740241.
Two harness connector generations exist across this production run — confirm your connector style before ordering. Harness adapters are available separately if your pigtail does not match.
