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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2006 🢒 TopKick C-Series (Conventional) C6/C7/C8 🢒 Vehicle Control Systems 🢒 Vehicle DTC Information 🢒 Power Take-Off (PTO) Does Not Engage

Circuit Description

This symptom chart will aid in diagnosing a failed Power Take-Off (PTO) solenoid engagement. This diagnostic will not expose a mechanical problem with the PTO itself. With the ignition switch in RUN or START, voltage is supplied through the Engine 1 fuse to the secondary side of the relay. When the relay is energized the contacts will close and voltage will be present at the load engage switch. When the operator needs the PTO he will close the load engage switch and current will flow to the PTO solenoid. The solenoid has its own external ground. When the operator turns the ignition switch to RUN, voltage will be present at the PTO enable switch. When the PTO enable switch is turned to ON voltage will be present at the coil of the relay and at the powertrain control module (PCM). If the PCM sees all of the conditions necessary to engage the solenoid, the PCM will ground the primary circuit of the relay. The operation of a diesel system is the same except that diesel engines have an engine control module (ECM) instead of a PCM.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests engine controls and cruise control for diagnostic trouble codes (DTCs).

    2.

  2. This step tests for an open Engine 1 fuse.

    3.

  3. This step tests the Power Distribution circuits.

    4.

  4. This step tests for voltage to the PTO solenoid.

    5.

  5. This step tests for continuity on the ground circuit.

    6.

  6. This step tests for voltage at the Ignition 1 Voltage and PTO On Switch-Signal circuits.

    7.

  7. This step tests the PTO control circuit.

    8.

  8. This step tests for continuity on the PTO control circuit.

    9.

  9. This step ensures that all of the PCM conditions for engaging the PTO are met.

    10.

  10. This step tests for ground on the Ignition 1 Voltage circuit.

    11.

  11. This step tests for a ground on the PTO supply voltage circuit.

    12.

  12. This step tests the PTO solenoid for an internal ground.

    13.

  13. This step tests for ground on the Ignition 1 Voltage circuit.

    14.

  14. This step tests for voltage at the PTO On Switch-Signal circuit.

    15.

  15. This step tests for voltage at the Ignition 1 Voltage circuit.

    16.

  16. This step tests the PTO Relay.

Step

Action

Yes

No

Schematic Reference: Power Take-Off (PTO) Schematics

1

Did you review the Power Take-Off (PTO) Description and Operation and perform the necessary inspections?

Go to Step 2

Go to Power Take-Off (PTO) Description and Operation

2

Did you perform the Diagnostic System Check - Vehicle?

Go to Step 3

Go to Diagnostic System Check - Vehicle

3

Inspect the Engine 1 fuse.

Is the fuse open?

Go to Step 11

Go to Step 4

4

  1. Turn the ignition switch to RUN.
  2. With a test lamp test for voltage to the Engine 1 fuse.

Does the test lamp light?

Go to Step 5

Go to Step 24

5

  1. Ensure that all of the PTO engage conditions are met. Refer to Power Take-Off (PTO) Description and Operation .
  2. Turn the PTO enable switch to ON.
  3. Turn the load engage switch to ON.
  4. With a test lamp test for voltage on the PTO Supply-Voltage circuit at the PTO solenoid.

Does the test lamp light?

Go to Step 6

Go to Step 7

6

With a DMM test for continuity on the ground circuit at the PTO solenoid.

Do you have continuity?

Go to Step 29

Go to Step 25

7

  1. Turn all switches OFF.
  2. Disconnect the relay connector.
  3. Turn the ignition switch to RUN.
  4. Turn the PTO enable switch to ON.

    5. Using a test lamp test for voltage at the Ignition 1 and PTO On Switch-Signal circuits at the relay connector.

Does the test lamp light on both tests?

Go to Step 8

Go to Step 16

8

  1. Turn all switches OFF.
  2. Connect the PTO relay.
  3. Turn the ignition switch to RUN.
  4. Turn the PTO enable switch to ON.
  5. Turn the load engage switch to ON.
  6. Ensure that all PTO Engage conditions are met. Refer to Power Take-Off (PTO) Description and Operation .
  7. Using a jumper wire ground the PTO Control circuit at the relay.

Does the PTO solenoid engage?

Go to Step 9

Go to Step 19

9

Test for continuity on the PTO Control circuit.

Does the PTO Control circuit have continuity?

Go to Step 10

Go to Step 26

10

Ensure that all of the PCM conditions for engaging the PTO are met. Refer to Power Take-Off (PTO) Description and Operation .

Are all of the conditions met?

Go to Step 31

Go to Step 27

11

  1. Remove the Engine 1 fuse.
  2. Disconnect the PTO relay.
  3. Using a DMM test for ground on the ignition 1 Voltage circuit at the relay connector.

Is the ignition 1 Voltage circuit grounded?

Go to Step 22

Go to Step 13

12

  1. Disconnect the PTO solenoid connector.
  2. Using a DMM test for ground on the PTO Supply-Voltage circuit at the relay connector.

Is the PTO Supply-Voltage circuit grounded?

Go to Step 23

Go to Step 29

13

  1. Disconnect both the positive and negative leads of the PTO solenoid.
  2. Using a DMM test for ground on the positive lead at the PTO solenoid.

Is the positive lead at the PTO solenoid grounded?

Go to Step 23

Go to Step 29

14

  1. Remove the Engine 1 fuse.
  2. Disconnect the PTO enable switch.
  3. Using a DMM test for ground on the Ignition 1 Voltage circuit at the switch connector.

Is the Ignition 1 Voltage circuit grounded?

Go to Step 21

Go to Step 15

15
  1. Disconnect the PTO Relay.
  2. Using a DMM test for ground on the PTO On Switch-Signal circuit at the relay connector.

Is the PTO On Switch-Signal circuit grounded?

Go to Step 20

Go to Step 28

16

Do you have voltage on the Ignition 1 Voltage circuit?

Go to Step 17

Go to Step 22

17

  1. Remove the PTO enable switch from the instrument panel but leave it connected to the harness.
  2. Using a fused jumper wire, jump from the Ignition 1 Voltage circuit to the PTO On Switch-Signal circuit at the switch.
  3. Using a test lamp test for voltage at the PTO On Switch-Signal circuit at the PTO relay connector.

Do you have voltage?

Go to Step 28

Go to Step 18

18

  1. Turn the ignition switch OFF.
  2. Turn the PTO enable switch OFF.
  3. Disconnect the PTO enable switch.
  4. Turn the ignition switch to RUN.
  5. Using a test lamp test for voltage at the Ignition 1 Voltage circuit at the switch connector.

Do you have voltage?

Go to Step 20

Go to Step 21

19

  1. Disconnect the PTO Relay.
  2. Using a fused jumper wire, jump from the Ignition 1 Voltage circuit to the PTO Supply-Voltage circuit at the relay connector.

Does the PTO Solenoid engage?

Go to Step 30

Go to Step 23

20

Repair the PTO on switch-signal circuit for an open, short to ground or high resistance. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 32

--

21

Repair the ignition 1 voltage circuit for an open, short to ground or high resistance. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 32

--

22

Repair the ignition 1 voltage circuit for an open, short to ground or high resistance. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 32

--

23

Repair the PTO supply-voltage circuit for an open, short to ground or high resistance. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 32

--

24

Repair the affected power distribution circuit for an open, short to ground or high resistance. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 32

--

25

Repair the ground circuit for an open, short to ground or high resistance. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 32

--

26

Repair the PTO control circuit for an open, short to ground or high resistance. Refer to Wiring Repairs .

Did you complete the repair?

Go to Step 32

--

27

Repair the malfunctioning PTO support circuit.

Did you complete the repair?

Go to Step 32

--

28

Replace the PTO enable switch. Refer to Upfitter instructions.

Did you complete the repair?

Go to Step 32

--

29

Replace the PTO solenoid. Refer to Upfitter instructions.

Did you complete the repair?

Go to Step 32

--

30

Replace the PTO relay. Refer to Upfitter instructions.

Did you complete the repair?

Go to Step 32

--

31

Replace the PCM or ECM. Refer to Control Module References for replacement, setup and programming.

Did you complete the repair?

Go to Step 32

--

32

Test drive the vehicle and operate the PTO system as described in the supporting text.

Does the symptom occur?

Go to Step 2

System OK