Sierra Classic 2500 4WD V8-6.0L (2007)
Power Take-Off: Testing and Inspection
Power Take-Off (PTO) Does Not Engage
Power Take-Off (PTO) Does Not Engage
Circuit Description
This symptom table aids in the diagnosis of a failed power take-off (PTO) solenoid engagement. This diagnostic does not expose a mechanical condition
with the PTO itself. Voltage is supplied at all times through the cruise fuse to the secondary side of the relay. When the relay is energized, the contacts
close and current is allowed to flow to the PTO solenoid. The solenoid has its own external ground. When the ignition switch is in the RUN position,
voltage is present at the PTO switch. When the PTO switch is in the ON position, voltage is present at the coil of the relay and at the PCM. If the PCM
sees all of the conditions necessary to engage the solenoid, the PCM grounds the primary circuit of the relay.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
2. This step tests for an open fog lamp fuse.
3. This step tests for open cruise fuse.
4. This step tests the battery positive circuit for battery voltage.
5. This step tests the battery positive circuit for an open.
6. This step tests the PTO relay output circuit for an open.
7. This step tests the PTO ON signal circuit for battery voltage.
8. This step tests the PTO ON signal circuit for an open.
9. This step tests the cruise control set/coast switch signal circuit for battery voltage.
10. This step tests the PTO status circuit for an open.
11. This step tests the PTO switch and PTO unit ground circuits for an open.
12. This step tests the battery positive and PTO relay output circuits for a short to ground.
13. This step tests the ignition 3 circuit for a short to ground.
14. This step tests the cruise control ON switch signal, cruise control set/coast signal, PTO status, and PTO ON signal circuits for a short to ground.
15. This step tests the control side of the PTO relay for proper operation.
