Scheme 1
Scheme 2
| Callout | Component Name |
|---|---|
| 1 | Fuse Block-Underhood |
| 2 | Engine Wiring Harness |
| 3 | Power Take Off (PTO) Relay |
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
- 2: Lack of communication may be due to a partial or total malfunction of the class 2 serial data circuit. The specified procedure will determine the particular condition.
- 3: The presence of DTCs indicates that the PCM or TAC has detected a fault.
- 4: The presence of DTCs which begin with "U" indicate some other module is not communicating. The specified procedure will compile all the available information before tests are performed.
- 5: This step insures that the PTO options in the scan tool are set according to the upfitters recommendations.
| Step | Action | Yes | No |
|---|---|---|---|
| 1 | Install a scan tool. Does the scan tool power up? | Go to Step 2 | Go to Scan Tool Does Not Power Up |
| 2 | Turn ON the ignition, with the engine OFF. Attempt to establish communication with the powertrain control module (PCM) for the 8.1L engine or the Engine Control Module (ECM) for the 6.6L diesel. Does the scan tool communicate with the control module? | Go to Step 3 | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications |
| 3 | Select the display DTCs function on the scan tool. Does the scan tool display any PCM or ECM DTCs? | Go to Step 4 | Go to Step 5 |
| 4 | Does the scan tool display any DTCs which begin with a "U"? | Go to Scan Tool Does Not Communicate with Class 2 Device in Data Link Communications | Go to Diagnostic Starting Point - Engine Controls or Diagnostic Starting Point - Cruise Control |
| 5 | View the PTO options on the scan tool to verify that the PTO settings are correct for the specific PTO application. Are the PTO settings correct? | Go to Symptoms - Power Take-Off (PTO) | Go to Step 6 |
| 6 | Change the PTO options as needed. See upfitter specifications in the upfitter installation manual. Are the PTO options set correctly? | Go to Symptoms - Power Take-Off (PTO) |
Diagnostic System Check - Power Take-Off (PTO)
Symptoms - Power Take-Off (PTO)
| IMPORTANT | The following steps must be completed before using the symptom tables. |
- Perform the «Diagnostic System Check - Power Take-Off (PTO)»(ref-184153-S27294862112005082200000) before using the Symptom Tables in order to verify that all of the following are true: There are no PCM or TAC module DTCs set. The PCM and TAC module can communicate to each other via the serial data links.
- Review the system operation in order to familiarize yourself with the system functions. Refer to «Power Take-Off (PTO) Description and Operation»(ref-184153-S39951792412005082200000) .
The numbers below refer to the step numbers on the diagnostic table.
- 2: This step tests for an open fog lamp fuse.
- 3: This step tests for open cruise fuse.
- 4: This step tests the battery positive circuit for battery voltage.
- 5: This step tests the battery positive circuit for an open.
- 6: This step tests the PTO relay output circuit for an open.
- 7: This step tests the PTO ON signal circuit for battery voltage.
- 8: This step tests the PTO ON signal circuit for an open.
- 9: This step tests the cruise control set/coast switch signal circuit for battery voltage.
- 10: This step tests the PTO status circuit for an open.
- 11: This step tests the PTO switch and PTO unit ground circuits for an open.
- 12: This step tests the battery positive and PTO relay output circuits for a short to ground.
- 13: This step tests the ignition 3 circuit for a short to ground.
- 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.
- 15: 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 a Diagnostic System Check - Power Take-Off? | Go to Step 2 | Go to Diagnostic System Check - Power Take-Off (PTO) |
| 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 | Turn the ignition ON, with the engine OFF. Set the PTO switch to ON. 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 | Set the parking brake. Start the engine. 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 PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls - 8.1L or Engine Control Module (ECM) Replacement in Engine Controls - 6.6L. Did you complete the repair? | Go to Step 19 | |
| 17 | Replace the PTO switch. Refer to Power Take-Off (PTO) Switch Replacement . Did you complete the repair? | Go to Step 19 | |
| 18 | Replace the PTO relay. Refer to Relay Replacement (Within an Electrical Center) Relay Replacement (Attached to Wire Harness) 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 |
Power Take-Off (PTO) Does Not Engage
The numbers below refer to the step numbers on the diagnostic table.
- 3: This step checks for other system DTCs that may affect the PTO.
- 6: This step tests the PCM for the PTO Enable signal.
- 7: This step tests the communication between the PCM and the TAC module.
- 8: This step tests the PTO On Switch Signal circuit.
- 9: This step tests the PTO On Switch-Signal circuit for an open, high resistance or short to ground.
- 10: This step tests the Serial Data circuits for an open, high resistance or short to ground.
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Power Take-Off (PTO) Schematics and Cruise Control Schematics in Cruise Control | |||
| 1 | Did you perform a Diagnostic System Check - Power Take-Off? | Go to Step 2 | Go to Diagnostic System Check - Power Take-Off (PTO) |
| 2 | Did you review the Power Take-Off Description and Operation and perform the necessary inspections? | Go to Step 3 | Go to Power Take-Off (PTO) Description and Operation |
| 3 | Verify the fault is present. Does the system operate normally? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 4 |
| 4 | Does the PTO solenoid engage? | Go to Step 5 | Go to Power Take-Off (PTO) Does Not Engage |
| 5 | Is the engine a 6.6L diesel? | Go to Step 8 | Go to Step 6 |
| 6 | Start the engine. Ensure that all of the PTO engage conditions are met. Refer to Power Take-Off (PTO) Description and Operation . Turn the PTO switch to ON. Using a scan tool read the PTO Enable Status on the Engine Controls Data List. Does the scan tool indicate that the PTO is enabled? | Go to Step 7 | Go to Step 9 |
| 7 | Using the scan tool read the TAC/PCM communication signal on the Engine Controls Data List. Does the scan tool display OK? | Go to Diagnostic Starting Point - Cruise Control | Go to Step 10 |
| 8 | Disconnect connector 1 at the ECM. Turn the ignition switch to ON. Turn the PTO switch to ON. Using a test lamp test for Voltage on the PTO On Switch Signal circuit. Does the test lamp light? | Go to Diagnostic System Check - Engine Controls in Engine Controls - 6.6L | Go to Step 9 |
| 9 | Test the PTO On Switch-Signal circuit for an open, high resistance or short to ground. Did you find and correct the condition? | Go to Step 13 | Go to Step 12 |
| 10 | Test the Serial Data circuits for an open, high resistance or short to ground. Refer to Cruise Control Schematics in Cruise Control. Did you find and correct the condition? | Go to Step 13 | Go to Step 11 |
| 11 | Replace the TAC module. Refer to Throttle Actuator Control (TAC) Module Replacement in Engine Controls - 8.1L. Did you complete the replacement? | Go to Step 13 | |
| 12 | Replace the PCM or ECM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls - 8.1L or Engine Control Module (ECM) Replacement in Engine Controls - 6.6L. Did you complete the replacement? | Go to Step 13 | |
| 13 | Test drive the vehicle and operate the PTO system as described in the supporting text. Does the symptom occur? | Go to Step 3 | System OK |
Engine RPM Does Not Increase with Power Take-Off Engaged
The number below refers to the step number on the diagnostic table.
- 5: This step tests the ground circuit.
| Step | Action | Yes | No |
|---|---|---|---|
| Schematic Reference: Power Take-Off (PTO) Schematics | |||
| 1 | Did you perform the Diagnostic System Check - Power Take-Off? | Go to Step 2 | Go to Diagnostic System Check - Power Take-Off (PTO) |
| 2 | Did you review the Power Take-Off Description and Operation and perform the necessary inspections? | Go to Step 3 | Go to Power Take-Off (PTO) Description and Operation |
| 3 | Verify the fault is present. Does the system operate normally? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 4 |
| 4 | Does the PTO solenoid engage? | Go to Step 5 | Go to Power Take-Off (PTO) Does Not Engage |
| 5 | Turn the ignition switch to RUN. Ensure that the conditions for engaging the PTO solenoid are met. Refer to Power Take-Off (PTO) Description and Operation . Remove the PTO switch but leave it connected to the harness. Turn the PTO switch to the ON position. Connect a fused jumper wire at the PTO switch connector ground circuit to a known ground. Does the indicator come on? | Go to Step 6 | Go to Step 7 |
| 6 | Repair the open or high resistance in both ground circuits 8 and 1850. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 8 | |
| 7 | Replace the PTO switch. Refer to Power Take-Off (PTO) Switch Replacement . Did you complete the replacement? | Go to Step 8 | |
| 8 | Test drive the vehicle and operate the PTO system as described in the supporting test. Does the symptom occur? | Go to Step 4 | System OK |
Power Take-Off (PTO) Indicator Inoperative
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
- PTO Switch
- Cruise Control Multi-Function Switch
- PTO Relay
- PTO Solenoid
- PCM with 8.1L gasoline only
- ECM with 6.6L diesel only
- TAC Module with 8.1L gasoline only
- 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.