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Power Take-Off (PTO) Does Not Engage




Power Take-Off (PTO) Does Not Engage

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Circuit/System Description

The power take-off (PTO) is an upfitter integrated system that allows the user to create an auxiliary power source. The PTO system specifically controls engine speed to values higher than normal base idle, PTO load relay engagement, and remote starting and shutdown of the engine. When the operator requests PTO using either the PTO switch or PTO remote, the engine RPM will increase to a default standby speed. The engine control module (ECM) converts the data from the engine speed sensor to a 2 pulses/engine revolution signal. When PTO is engaged, the power take-off module (PTOM) sends a GMLAN serial data message to the ECM requesting engine speeds, in accordance with the depressed switches from the PTO switch or remote.

Reference Information

Schematic Reference

Power Take-Off (PTO) Schematics [1][2]Electrical Diagrams

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Description and Operation

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

Electrical Information Reference

* Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

1. Engine ON, observe the PTO In Cab Switch parameter with a scan tool. Press 1 on the PTO switch to engage PTO. The engine RPM should increase to the default engine speed within a few seconds. Press 0 to disengage PTO and to return the engine speed back to normal idle. The PTO In Cab Switch parameter should change accordingly with the depressed switch.

2. Engine OFF, key out of ignition, observe the PTO Remote Switch Status with a scan tool. Enable PTO using the upfitted remote switch assembly (if equipped). The engine RPM should increase to the default engine speed within a few seconds. Use the upfitted remote switch assembly to disengage PTO and the engine should shut down. The PTO Remote Switch Status parameter should change accordingly with the depressed remote switch.

Circuit/System Testing

PTO In Cab Switch

1. Ignition OFF, disconnect the harness connector at the PTO module.

2. Ignition ON, test for 11 volts or greater between the B+ circuit terminal 32 and ground.

• If less than the specified voltage, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect the harness connector at the PTO module.

4. Ignition OFF, disconnect the harness connector at the PTO switch.

5. Ignition ON, test for 4.8-5.2 volts between the 5V reference circuit terminal 1 and ground.

• If less than the specified range, test the 5V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the PTO module.

• If greater than the specified range, test the 5V reference circuit for a short to voltage. If a short to voltage is found and repaired, replace the PTO switch. If the circuit tests normal, replace the PTO module and the PTO switch.

6. Connect the harness connector at the PTO switch.

7. Engine ON, observe the PTO In Cab Switch parameter with a scan tool. Verify that the PTO In Cab Switch parameter matches each depressed switch: 1, 0, RES +, SET -.

• If any one of the switches do not match accordingly with the scan tool parameter, replace the PTO switch.

8. If all circuits test normal, replace the PTO module.

Upfitted Remote Switch Assembly

1. Ignition OFF, disconnect the harness connector at the PTO module.

2. Ignition ON, test for 11 volts or greater between the B+ circuit terminal 32 and ground.

• If less than the specified voltage, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect the harness connector at the PTO module.

4. Ignition OFF, disconnect the harness connector X124.

5. Ignition ON, test for 4.8-5.2 volts between the 5V reference circuit terminal E and ground.

• If less than the specified range, test the 5V reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the PTO module.

• If greater than the specified range, test the 5V reference circuit for a short to voltage. If the circuit tests normal, replace the PTO module.

6. Connect the harness connector X124.

7. Engage PTO using the upfitted remote switch assembly. Observe the PTO Remote Switch Status parameter with a scan tool. Verify that the PTO Remote Switch Status parameter matches each depressed switch.

• If any one of the switches do not match accordingly with the scan tool parameter or if PTO does not engage, replace the upfitted remote switch assembly.

8. If all circuits test normal, replace the PTO module.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Control Module References Control Module References for PTO module replacement, setup, and programming

* Power Take-Off Switch Replacement Power Take-Off Switch Replacement

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