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Test Description

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

  1. 4:  This step tests for the signal voltage that represents atmospheric pressure. Removing the fuel fill cap ensures a vented EVAP system. Record the value for possible use later in the diagnostic table.
  2. 7:  This step tests the accuracy of the FTP sensor by comparing the electrical signal value to the EEST mechanical gage value.
  3. 8:  A restricted EVAP system will not allow the nitrogen to flow freely through the system. A restriction will cause the FTP signal voltage parameter to decrease as the pressure builds.
DTC P0451

Step
 		 Action Values Yes No
Schematic Reference: Evaporative Emissions (EVAP) Hose Routing Diagram and Engine Controls Schematics
Connector End View Reference: Engine Control Module (ECM) Connector End Views or Engine Controls Connector End Views
1 Did you perform the Diagnostic System Check - Vehicle? - Go to Step 2  Go to Diagnostic System Check - Vehicle
2 Is DTC P0446, P0452, P0453, or P0651 also set? - Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Step 3 
3 Inspect the evaporative emission (EVAP) system for the following conditions:
Did you find and correct the condition?		 - Go to Step 17  Go to Step 4 
4 
  1. Remove the fuel fill cap.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe and record the fuel tank pressure (FTP) parameter in volts with a scan tool.
Is the fuel tank pressure sensor parameter within the specified amount?		 1.3-1.7 V Go to Step 5  Go to Step 14 
5
IMPORTANT: Ensure that the vehicle underbody temperature is similar to the ambient temperature.
  1. Turn OFF the ignition.
  2. Install the fuel fill cap.
  3. Connect the J 41413-200  Evaporative Emission System Tester (EEST) power supply clips to a known good 12-volt source. See Special Tools .
  4. Install the J 41415-40  Fuel Tank Cap Adapter or the GE-41415-50  Fuel Cap Adapter to the fuel fill pipe. See Special Tools .
  5. Connect the J 41413-200  NITROGEN/SMOKE supply hose to the J 41415-40  or the GE-41415-50  to the fuel fill pipe. See Special Tools .
  6. Turn the ignition ON, with the engine OFF.
  7. Turn the NITROGEN/SMOKE valve on the J 41413-200  to NITROGEN. See Special Tools .
  8. Using a scan tool PURGE/SEAL function, seal the EVAP system.
  9. Observe the fuel tank pressure sensor in H2O using a scan tool.
  10. Use a remote switch to pressurize the EVAP system to the first specified value.
  11. Allow at least 30 seconds for pressure in the EVAP system to stabilize. Compare the fuel tank pressure (FTP) parameter in H2O to the J 41413-200  VACUUM/PRESSURE gage. See Special Tools .
Is the difference between the FTP parameter on a scan tool and the VACUUM/PRESSURE gage on the J 41413-200  within the second specified value? See Special Tools .		 5 in H2O
1 in H2O		 Go to Step 6  Go to Step 14 
6 Release the pressure on the EVAP system with the scan tool.
Is the difference between the FTP parameter on the scan tool and the VACUUM/PRESSURE gage on the J 41413-200  within the specified value. See Special Tools .		 1 in H2O Go to Step 7  Go to Step 14 
7 
  1. Start the engine.
  2. Allow the engine to idle.
    3. IMPORTANT: Using more than 20 percent purge can cause a misdiagnosis.
  3. Use the PURGE/SEAL function of a scan tool to command 20 percent purge.
  4. Observe the VACUUM/PRESSURE gage on the J 41413-200  and the fuel tank pressure parameter on the scan tool. See Special Tools . Allow the vacuum to increase to the first specified value.
Is the difference between the FTP parameter on the scan tool and the VACUUM/PRESSURE gage on the J 41413-200  within the second specified value. See Special Tools .		 5 in H2O
1 in H2O		 Go to Step 8  Go to Step 14 
8 
  1. Turn ON the ignition, with the engine OFF.
  2. Turn the NITROGEN/SMOKE valve on the J 41413-200  to NITROGEN. See Special Tools .
  3. Observe the FTP sensor in volts using a scan tool.
  4. Pressurize the EVAP system with the remote switch.
  5. Allow enough time for pressure to stabilize.
Is the difference between the observed FTP sensor voltage and the voltage recorded in Step 4 more than the specified value?		 0.2 V Go to Step 9  System OK
9
  1. Disconnect the EVAP vent hose from the EVAP canister vent solenoid valve with pressure still applied from the J 41413-200  . See Special Tools . Refer to Emission Hose Routing Diagram .
  2. Observe the FTP sensor in volts using a scan tool.
Is the difference between the observed FTP sensor voltage and the voltage recorded in Step 4 more than the specified value?		 0.2 V Go to Step 10  Go to Step 11 
10
  1. Disconnect the EVAP vapor pipe from the EVAP canister with pressure still applied from the J 41413-200  . See Special Tools . Refer to Emission Hose Routing Diagram .
  2. Observe the FTP sensor in volts using a scan tool.
Is the difference between the observed FTP sensor voltage and the voltage recorded in Step 4 more than the specified value?		 0.2 V Go to Step 13  Go to Step 12 
11 Repair or replace the EVAP canister vent solenoid. Refer to Evaporative Emission (EVAP) Canister Vent Solenoid Valve Replacement .
Did you complete the action?		 - Go to Step 17  -
12 Replace the EVAP canister. Refer to Evaporative Emission (EVAP) Canister Replacement .
Did you complete the replacement?		 - Go to Step 17  -
13 Repair or replace the pinched or restricted EVAP vapor pipe. Refer to Evaporative Emissions (EVAP) Hose Routing Diagram .
Did you complete the action?		 - Go to Step 17  -
14 Test for an intermittent and for a poor connection at the FTP sensor. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 17  Go to Step 15 
15 Test the low reference circuit of the FTP sensor for an open or high resistance. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 17  Go to Step 16 
16 Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .
Did you complete the replacement?		 - Go to Step 17  -
17
  1. Reconnect all components and release any pressure or vacuum applied to the EVAP system.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe and record the fuel tank pressure (FTP) parameter in H2O with a scan tool.
Is the fuel tank pressure sensor parameter within the specified amount?		 -1 to +1 in H2O Go to Step 18  Go to Step 2 
18
  1. Turn ON the ignition, with the engine OFF.
  2. Command the EVAP canister vent solenoid closed with a scan tool.
  3. Turn the NITROGEN/SMOKE valve on the J 41413-200  to NITROGEN. See Special Tools .
  4. Pressurize the EVAP system to the first specified value with the remote switch.
  5. Observe the fuel pressure sensor in H2O using a scan tool.
  6. Command the EVAP canister vent solenoid valve open with a scan tool.
Is the fuel tank pressure sensor parameter less than the second specified value?		 5 in H2O
1 in H2O		 Go to Step 19  Go to Diagnostic Aids
19 Observe the Capture Info with a scan tool.
Are there any DTCs that have not been diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List - Vehicle Go to Step 20 
20
IMPORTANT: The malfunction indicator lamp (MIL) may remain ON after the repair unless the DTCs are cleared.
Clear the DTCs with a scan tool.Did you complete the action?		 - System OK -
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