Err 3 means the controller does not yet know the camshaft position. At initial power-up, the manual says the camshaft may take one to two minutes to return home and Err 3 remains during that movement. A persistent display requires observation and manual-specific troubleshooting, not an immediate cam replacement.
Decision sequence
- Allow the documented one-to-two-minute initial homing period and confirm the hourglass indicates motor operation.
- If Err 3 persists beyond the initial period, observe whether the motor turns the camshaft.
- Under the troubleshooting table, verify the motor connection and wire harness before selecting a motor or cam.
- If the cam turns without finding home, inspect the body-specific cam timing cup and optical sensor under the manual.
- Do not rotate the camshaft by hand while the motor is installed; the manual warns to use the controller to step cycles.
Body-specific parts remain separate
| Reference | Role | Boundary |
|---|---|---|
| 1235361 | Motor/optical cable assembly | Confirm controller, wiring, and body before replacement. |
| 1235373 | Photo interrupter sensor module | Sensor condition is one diagnosis branch, not the meaning of every Err 3. |
| 1235353 | 255/700–860 standard black cam | Not the Performa cam. |
| 1235352 | 263–268/700–860 standard black cam | Not the 255 cam. |
Record the valve-body label, controller, displayed code, whether the hourglass flashes, and whether the cam moves before using the fitment form.
Service safety and limits
These checks identify a valve and narrow a parts search; they are not a substitute for the manufacturer service procedure. Before opening a valve, use the documented bypass procedure, isolate water, relieve pressure, and disconnect power. Water-treatment valve service should be performed by a qualified person. Stop if the label, flow direction, wiring, or part suffix does not match the cited manual.
Primary source
Pentair Autotrol 742/762 Control 255 & Performa Series Valves Service Manual, document 3000440, ©2024, printed page 3 initial power-up, pages 23–24 drive/sensor sections, and page 37 troubleshooting.
Revision status: no superseding revision is asserted. Verify the revision block in the linked manufacturer document. Evidence reviewed September 28, 2026.