Engine Preset PTO Speed Returns to Idle (Install Relay)

Some drivers may comment that engine speed power takeoff (PTO) operation returns to idle for no apparent reason.

Erratic signals from the Vehicle Speed Sensor (VSS) may result in the Engine Control Module shutting off the PTO fast idle system.

Install a relay, controlled by the automatic transmission position switch, in the PTO enable signal circuit and reset the PTO fast idle system vehicle speed limit. This excludes the VSS parameter from the PTO fast idle system and allows PTO operation only with the transmission in "Neutral". Use the service procedure and the part numbers listed below.

1. Obtain standard stock 12-gauge wire and cut into two wires to a length of 2134 mm (84 in) each.
2. Obtain standard stock 14- gauge wire and cut into two wires; one to a length of 2134 mm (84 in) and the other to a length of 610 mm (24 in).
3. Strip 10 mm (3/8 in) of insulation from each end of the wires.
4. On connector pack P/N 15306045, do the following steps:

•	Cut the lead from cavity 87A as close to the connector as possible. This terminal is not used for this application. Apply a small amount of silicone on the end of the cut wire within the connector in order to seal out possible moisture intrusion.

•	Stagger the lengths of the leads at cavities 30, 84, and 87 in order to eliminate stacking of the splices.

•	Strip 10 mm (3/8 in) of insulation from each end of the remaining leads.

5. Using the 12-gauge wire cut to a length of 2134 mm (84 in), connect to the lead at cavity 30 of the connector. Follow the splice instructions provided with the connector pack.
6. Using the 12-gauge wire cut to a length of 2134 mm (84 in), connect to the lead at cavity 87 of the connector. Follow the splice instructions provided with the connector pack.
7. Using the 14-gauge wire cut to a length of 2134 mm (84 in), connect to the lead at cavity 85 of the connector. Follow the splice instructions provided with the connector pack.
8. Using the 14-gauge wire cut to a length of 610 mm (24 in), connect to the lead at cavity 86 of the connector. Follow the splice instructions provided with the connector pack.
9. Label the wire ends with cavity numbers for future reference.
10. Install the 13 mm (1/2 in) of plastic conduit over the wires from cavities 30, 85, and 87. Install the 6 mm (1/4 in) of plastic conduit over the wire from cavity 86.
11. Connect the harness to the relay P/N 12193601.
12. Open the hood.
13. Mount the relay onto the bracket attached to the front of dash panel underneath the right side bulkhead pass through connector. Snap the relay into place on the bracket.
14. Take the wire from cavity 86 of the relay and splice onto the orange and black wire (circuit 1786) of the right side bulkhead pass through connector.
15. Take the remaining wires and run them along the frame rail down to the transmission.
16. Raise the vehicle.
17. Take the wire from cavity 85 and splice into a ground wire at the block on the right frame rail.
18. Locate the wire coming from the PTO switch to the PTO solenoid. Cut that wire and strip 10 mm (3/8 in) of insulation from the ends. This wire may be dark blue in color, depending on upfitter provisions.
19. Connect the wire from cavity 30 to the wire end coming from the PTO switch.
20. Connect the wire from cavity 87 to the other wire end.
21. Solder and properly seal all connections. Refer to the Wiring Systems sub-section of the Service Manual.
22. Carefully secure the harness using tie straps to ensure proper routing and clearance from sharp objects or pinch points.
23. Using the CAT ET, adjust the PTO vehicle speed limit to the maximum range of 204 km/h (127 mph). See Service Information for instructions. In this configuration, the Engine Control Module will no longer read the erratic VSS signal.
24. Instruct the driver to place the transmission in "Neutral" before running the PTO.

Parts are currently available from GMSPO.

For vehicles repaired under warranty, use: