For 1990-2009 cars

### 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 or any fault with a specific upfitter part. This symptom chart will diagnose original equipment parts only. Refer to upfitter instructions for upfitter supplied parts. Voltage is supplied with the ignition switch in RUN and START through the ignition switch circuit breaker to the PTO Switch. When the PTO Switch is turned to ON, voltage will be present at the PTO Switch Output Enable circuit at both the PCM and the PTO upfitter connector. When the PCM sees all the necessary conditions to turn the PTO Solenoid ON it will provide a ground for the PTO Relay on the PTO Control circuit. When the PTO Relay is energized the contacts will close and current will flow to the PTO Solenoid. The PTO Solenoid has its own ground wire.

### Test Description

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

1. This step tests Engine Controls and Cruise Control for DTCs.

2. This step tests for shorts to ground.

3. This step tests for voltage on the Ignition 1 Voltage circuit.

4. This step tests for voltage on the PTO Switch Output Enable circuit.

5. This step tests for voltage on the PTO Switch Output Enable circuit at the PCM and Upfitter connector.

6. This step tests for continuity on the PTO Engage Signal circuit.

7. This step tests the PCMs ability to ground the PTO Control circuit.

8. This step tests for the location of the short to ground.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Power Take-Off (PTO) Schematics
1 | Did you review the Power Take-Off 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 a Diagnostic System Check? | Go to Step 3 | Go to Diagnostic System Check - Power Take-Off (PTO)
3 |

1. Remove the ignition switch circuit breaker.
2. Install a 20 Amp fuse.
3. Ensure that all of the PTO engage conditions are met. Refer to Power Take-Off (PTO) Description and Operation .
4. Turn the ignition switch to RUN.
5. Observe the fuse.
6. Turn the PTO switch ON
7. Observe the fuse.

Is the fuse open?

Go to Step 09

Go to Step 4

4 |

1. Remove the PTO Switch and leave it connected to the harness.
2. With a test lamp test for voltage at the Ignition 1 Voltage circuit.

Does the test lamp light?

Go to Step 5

Go to Step 11

5 | With a test lamp test for voltage at the PTO On Switch-Signal circuit at the PTO Switch. Does the test lamp light? | Go to Step 6 | Go to Step 13
6 |

1. Turn the Ignition Switch and the PTO Switch OFF.
2. Disconnect the PCM and the PTO Upfitter connectors.
3. Turn the Ignition Switch and the PTO Switch ON.
4. With a test lamp test for voltage at the PTO On Switch-Signal circuits at the PCM and the PTO Upfitter connectors.

Did the test lamp light on both tests?

Go to Step 7

Go to Step 10

7 |

1. Turn the PTO and Ignition switch OFF.
2. Using a DMM measure continuity on the PTO Control circuit.

Do you have continuity?

Go to Step 8

Go to Step 12

8 |

1. Connect the PCM and PTO Upfitter connectors.
2. Turn the ignition switch to RUN and the PTO Switch to ON.
3. Connect a fused jumper wire at the PTO Control circuit at the PCM connector to a known ground.
4. Ensure that all PTO Engage conditions are met. Refer to Power Take-Off (PTO) Description and Operation .

Does the PTO solenoid engage?

Go to Step 14

Go to Step 15

9 | Did the fuse open before the PTO Switch was turned on? | Go to Step 11 | Go to Step 10
10 | Repair the PTO On Switch-Signal circuit for an open, short to ground or high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 16 | --
11 | Repair the Ignition 1 Voltage circuit for an open, short to ground or high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 16 | --
12 | Repair the PTO Control circuit for an open, short to ground or high resistance. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 16 | --
13 | Replace the PTO switch. Refer to Upfitter instructions. Did you complete the repair? | Go to Step 16 | --
14 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls - 8.1L. Did you complete the repair? | Go to Step 16 | --
15 | Repair the Upfitter supplied or installed parts or wiring. Refer to Upfitter repair manual. Did you complete the repair? | Go to Step 16 | --
16 | 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