Power Take-Off System Chevrolet Cab & Chassis Silverado 3500

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Power Take Off (PTO) Relay Connector & Terminal Parts Information

Power Take Off (PTO) Relay Terminal Identification

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Power Take Off (PTO) Switch Connector & Terminal Parts Information

Power Take Off (PTO) Switch Terminal Identification

Symptoms - Power Take-Off (PTO)

1. Perform the «Diagnostic System Check - Vehicle»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/oem-general-information/#vehicle-diagnostic-information__diagnostic-system-check-vehicle) , before using the Symptom Tables in order to verify that all of the following are true: There are no powertrain control module (PCM) or throttle actuator control (TAC) module DTCs set. The PCM and TAC module can communicate to each other via the serial data links.
2. Review the system operation in order to familiarize yourself with the system functions. Refer to «Power Take-Off (PTO) Description and Operation»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/power-takeoff/#power-take-off-system__power-take-off-pto-description-and-operation) .

Visual/Physical Inspection

1. Inspect the upfitter connections of the PTO system. Refer to «Checking Aftermarket Accessories»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/ignition-switchsteering-lock/#wiring-systems-and-power-management-troubleshooting-diagnosis__checking-aftermarket-accessories) .
2. Inspect the easily accessible, or the visible system components for obvious damage or conditions which could cause the symptom.
3. Inspect the transmission and the hydraulic pump for the proper fluid level.

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to a symptom diagnostic procedure from the following list in order to diagnose the symptom

1. «Power Take-Off (PTO) Does Not Engage»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/power-takeoff/#power-take-off-system)
2. «Engine RPM Does Not Increase with Power Take-Off Engaged»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/power-takeoff/#power-take-off-system)
3. «Power Take-Off (PTO) Indicator Inoperative»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/power-takeoff/#power-take-off-system)

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. 2: This step tests for an open fog lamp fuse.
2. 3: This step tests for open cruise fuse.
3. 4: This step tests the battery positive circuit for battery voltage.
4. 5: This step tests the battery positive circuit for an open.
5. 6: This step tests the PTO relay output circuit for an open.
6. 7: This step tests the PTO ON signal circuit for battery voltage.
7. 8: This step tests the PTO ON signal circuit for an open.
8. 9: This step tests the cruise control set/coast switch signal circuit for battery voltage.
9. 10: This step tests the PTO status circuit for an open.
10. 11: This step tests the PTO switch and PTO unit ground circuits for an open.
11. 12: This step tests the battery positive and PTO relay output circuits for a short to ground.
12. 13: This step tests the ignition 3 circuit for a short to ground.
13. 14: 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. 15: This step tests the control side of the PTO relay for proper operation.

Power Take-Off (PTO) Does Not Engage

When the power take-off (PTO) switch is turned to the ON position and all PTO engage conditions are met, the engine RPM should increase to the standby speed. When the powertrain control module (PCM) receives the signal from the PTO switch the PCM will send a signal to the throttle actuator control module (TAC). The TAC module controls the TAC motor which changes the position of the throttle. Communications between the two modules is monitored and checked for accuracy by the PCM. DTCs may be recorded in the event of the failure. The 6.6L diesel engine does not have a TAC system and the engine RPM is strictly controlled by the engine control module (ECM) and the Fuel Injection Control Module.

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

1. 3: This step checks for other system DTCs that may affect the PTO.
2. 6: This step tests the PCM for the PTO Enable signal.
3. 7: This step tests the communication between the PCM and the TAC module.
4. 8: This step tests the PTO On Switch Signal circuit.
5. 9: This step tests the PTO On Switch-Signal circuit for an open, high resistance or short to ground.
6. 10: This step tests the Serial Data circuits for an open, high resistance or short to ground.

Engine RPM Does Not Increase with Power Take-Off Engaged

This symptom chart will aid in diagnosing a failed power take-off (PTO) indicator. This diagnostic assumes that the PTO solenoid is functional and only the indicator is failing to come on. When the ignition switch is in RUN, voltage should be present on the Ignition 3 Voltage circuit. When the PTO switch is turned to ON, the LED will illuminate. The indicator has its own ground circuit. The LED and PTO solenoid have different ground circuits. Therefore, the LED may be illuminated when the PTO solenoid is disengaged.

The number below refers to the step number on the diagnostic table.

1. 5: This step tests the ground circuit.

Power Take-Off (PTO) Indicator Inoperative

Removal Procedure

1. Remove the I/P cluster bezel. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .
2. Pull out the switch housing from the I/P.
3. Disconnect the wire connector to the PTO switch.
4. Remove the PTO switch from the switch housing.

Installation Procedure

1. Install the PTO switch to the housing
2. Connect the wire connector to the switch.
3. Install the switch housing to the I/P till it clicks into place.
4. Install the I/P cluster bezel. Refer to «Instrument Panel Cluster Trim Plate Bezel Replacement»(/chevrolet/cab-chassis-silverado-3500/2003-2012/remont/exteriorinterior-trim/#instrument-panel-trim-and-console-trim) .

Power Take-Off (PTO) Description and Operation

The PTO is an Upfitter integrated system that allows the user to create an auxiliary power source that will drive either a hydraulic pump or a generator. When the operator requests PTO the PTO switch will be turned ON and the engine RPM will go to a default standby speed. The operator will then press and release the PTO switch to SET and the PTO solenoid will engage. Turning the PTO switch to OFF or pressing the brake pedal will turn the PTO off.

The PTO system is integrated with the Cruise Control system and Engine Controls. The PTO system utilizes the following parts

1. PTO Switch
2. Cruise Control Multi-Function Switch
3. PTO Relay
4. PTO Solenoid
5. PCM with 8.1L gasoline only
6. ECM with 6.6L diesel only
7. TAC Module with 8.1L gasoline only
8. TAC Motor with 8.1L gasoline only

Voltage will be supplied at all times through the Fog Lamp fuse to the secondary side of the PTO Relay. When the operator turns the ignition switch to RUN, voltage will be supplied through the Cruise fuse to the open PTO switch.

When the PTO switch is turned ON voltage will be present through the primary side of the PTO Relay and at the PCM. If the PCM sees all of the requirements for PTO engagement the PCM will send a Class 2 signal to the TAC Module. The TAC Module will use the TAC Motor to increase the engine RPM to the standby speed. When the PTO switch is turned to the SET position and released the PCM will ground the primary side of the PTO Relay. Current will flow through the coil in the PTO Relay and close the normally open contacts. This will allow current to flow to the PTO Solenoid and eventually to ground.

In the event that any of the PTO requirements are no longer met then the PCM or TAC will return the engine RPM to idle and turn the PTO Solenoid off.

PTO - Preset Mode (Factory Default Setting)

The PTO preset mode is used for stationary applications. PTO will remain engaged while mobile in the preset mode however PTO Preset 1 and PTO Preset 2 speed controls will be inoperative. The engine RPM will also return to normal. This mode provides a default standby speed of 800 or 850 RPM depending on the engine and transmission combination. This mode also provides 2 default PTO control speeds: PTO Preset 1 of 1250 RPM and PTO Preset 2 of 1700 RPM. Please note that the standby speed is not to be used as a PTO control speed. Vehicles not equipped with cruise control will not have the resume speed capability.

Power Take-Off (PTO) Description and Operation

PTO Preset Mode Function Chart

PTO - Variable Mode

The PTO speed control mode is used for both stationary and mobile applications. This mode allows PTO to be controlled in a fashion similar to cruise control. The operator is able to hold an engine RPM between 800 and 2200 with the SET switch on the cruise stock or the PTO switch. The operator can "tap up" to increase engine speed in 100 RPM increments with the RESUME switch. The operator may also "tap down" to decrease engine speed with either SET switch on the cruise control multifunction switch or the PTO switch. Vehicles not equipped with cruise control will not have the "tap up" capability.

Power Take-Off (PTO) Description and Operation

PTO - Variable Mode Function Chart

PTO Components

PTO Switch

The PTO Switch is mounted in the center of the Instrument Panel. The PTO Switch has three positions: OFF, ON and SET. When the PTO switch is in ON voltage will be present on the PTO On Switch Signal circuit at the relay and the PCM. When the switch is held to the SET position, voltage will be present on the PTO Engage Signal circuit at the PCM. The PTO indicator light is integral with the switch and will illuminate when the switch is turned ON. The presence of the indicator being on does not mean that the PTO Solenoid is engaged. The Cruise Control Multi-Function Switch may be used in conjunction with the PTO Switch. Illumination of the switch is provided through the dimming circuit and controlled in part by internal switch logic.

Cruise Control Multi-Function Switch

The operation of the PTO system may be through the function control switches located on the multifunction turn signal lever. The cruise control function control switches includes the ON/OFF, SET/COAST, and R/A. The switch assembly provides driver control of the PTO as well as the cruise control system. The SET/COAST and R/A switches may be used to increase and decrease engine RPM in increments of 100 RPM. See the chart below for recommended speeds.

PTO Relay

The PTO Relay is located on the side of the underhood fuse block. The secondary side of the relay is supplied with voltage at all times through the Fog Lamp fuse. The PTO switch controls the voltage to the primary side of the PTO relay while the PCM controls the ground.

PTO Solenoid

The solenoid is an upfitter supplied part and is replaceable on most PTOs. The PTO solenoid is used on clutch activated PTOs. The PTO relay supplies the solenoid with voltage when the relay is energized.

PCM

The powertrain control module (PCM) is the control center of the PTO system. Applications with a 6.6L diesel use an ECM. The PCM monitors numerous engine and vehicle functions. To engage the PTO, the PCM must see the following conditions

1. PTO switch is ON
2. Engine must be running
3. Transmission must be in PARK or NEUTRAL
4. Park Brake must be set for manual transmission only
5. Vehicle speed must be zero in Preset Mode only
6. Brake or Clutch must not be depressed

TAC Module

The TAC module is the control center for the electronic throttle system. The TAC module and the PCM communicate through a dedicated redundant serial data circuit. The TAC module and the PCM monitor the commanded throttle position and compare the commanded position to the actual throttle position. This is accomplished by monitoring the APP and the throttle position (TP) sensor. These 2 values must be within a calibrated value of each other or a DTC may be set. The TAC module also monitors each individual circuit of the TP sensor and the APP to verify proper operation. The TAC module commands the TAC motor to increase or decrease the engine RPM.

TAC Motor

The TAC motor is part of the throttle body and controls the positions of the throttle. The motor is bi-directional and is controlled by the TAC module. The TAC motor increases or decreases the engine RPM.

See also:
• Diagnostic System Check - Vehicle
• Checking Aftermarket Accessories
• Testing for Intermittent Conditions and Poor Connections
• Circuit Protection - Fuses
• Testing for Continuity
• Wiring Repairs
• Testing for Short to Ground
• Control Module References
• Relay Replacement (Attached to Wire Harness)
• Cruise Control Schematics
• Diagnostic Starting Point - Cruise Control
• Instrument Panel Cluster Trim Plate Bezel Replacement
• Power Take-Off (PTO) Description and Operation
• Power Take-Off (PTO) Does Not Engage