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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 GMC Sierra Denali 🢒 Accessories 🢒 Power Take-Off 🢒 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.

  1. This step tests for an open fog lamp fuse.

    2.

  2. This step tests for open cruise fuse.

    3.

  3. This step tests the battery positive circuit for battery voltage.

    4.

  4. This step tests the battery positive circuit for an open.

    5.

  5. This step tests the PTO relay output circuit for an open.

    6.

  6. This step tests the PTO ON signal circuit for battery voltage.

    7.

  7. This step tests the PTO ON signal circuit for an open.

    8.

  8. This step tests the cruise control set/coast switch signal circuit for battery voltage.

    9.

  9. This step tests the PTO status circuit for an open.

    10.

  10. This step tests the PTO switch and PTO unit ground circuits for an open.

    11.

  11. This step tests the battery positive and PTO relay output circuits for a short to ground.

    12.

  12. This step tests the ignition 3 circuit for a short to ground.

    13.

  13. 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.

    14.

  14. This step tests the control side of the PTO relay for proper operation.

Step

Action

Yes

No

Schematic Reference: Power Take-Off (PTO) Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 2

Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

2

Inspect the fog lamp fuse for an open.

Refer to Circuit Protection - Fuses in Wiring Systems.

Is the fuse open?

Go to Step 12

Go to Step 3

3

Inspect the cruise fuse for an open.

Refer to Circuit Protection - Fuses in Wiring Systems.

Is the fuse open?

Go to Step 13

Go to Step 4

4

Using a DMM, test the battery positive voltage circuit for voltage.

Does the DMM indicate battery voltage?

Go to Step 7

Go to Step 5

5

Using a DMM, test the battery positive circuit for an open or high resistance.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Step 6

6

Using a DMM, test the PTO relay output circuit for an open or high resistance.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Step 7

7
  1. Turn the ignition ON, with the engine OFF.
  2. Set the PTO switch to ON.
  3. Using a DMM at the PTO relay, test for voltage on the PTO ON signal circuit.

Does the DMM indicate battery voltage?

Go to Step 9

Go to Step 8

8

Using a DMM, test the PTO ON signal circuit for an open or high resistance.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Step 9

9
  1. Set the parking brake.
  2. Start the engine.
  3. While pressing the PTO set switch, use a DMM to test for voltage on the cruise control set/coast switch signal circuit at the PTO unit.

Does the DMM indicate battery voltage?

Go to Step 15

Go to Step 10

10

Using a DMM, test the PTO status circuit for an open or high resistance.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Step 11

11

Using a DMM, test the PTO switch and PTO unit ground circuits for an open or high resistance.

Refer to Testing for Continuity and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Step 17

12

Using a DMM, test the battery positive and PTO relay output circuits for a short to ground.

Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Step 18

13

Using a DMM, test the ignition 3 voltage circuit for a short to ground.

Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Step 14

14

Using a DMM, test the cruise control ON switch signal, cruise control set/coast signal, PTO status, and the PTO ON signal circuit for a short to ground.

Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 19

Go to Inducing Intermittent Fault Conditions in Wiring Systems

15

With the PTO ON, use a fused jumper wire to ground the PTO control circuit.

Does the PTO relay turn ON?

Go to Step 16

Go to Step 18

16

Replace the powertrain control module (PCM). Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming.

Did you complete the repair?

Go to Step 19

--

17

Replace the PTO switch.

Refer to Power Take-Off Switch Replacement .

Did you complete the repair?

Go to Step 19

--

18

Replace the PTO relay.

Refer to Relay Replacement in Wiring Systems.

Did you complete the repair?

Go to Step 19

--

19

Operate the PTO system as described in the supporting text.

Does the symptom occur?

Go to Step 2

System OK