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Test Description

WARNING: This page is about a different car, the 2004 GMC Sierra, 2004 GMC Cab & Chassis Sierra, 2004 Chevrolet Silverado, and 2004 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.

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

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 
  1. Start the engine.
  2. Ensure that all of the PTO engage conditions are met. Refer to Power Take-Off (PTO) Description and Operation .
  3. Turn the PTO switch to ON.
  4. 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 
  1. Disconnect connector 1 at the ECM.
  2. Turn the ignition switch to ON.
  3. Turn the PTO switch to ON.
  4. 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
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