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Test Description

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

  1. 2:  This step verifies that the condition is present.
  2. 4:  The ECM produces a measurable steady state amperage that provides the 5-volt reference to the FTP sensor. If the amperage on the 5-volt reference circuit is less than 80 mA, test the 5-volt reference circuit for an open or high resistance.
  3. 5:  This step tests the signal circuit of the FTP sensor.
  4. 6:  This step tests for high resistance in the low reference circuit of the FTP sensor. The ECM must be completely powered down to obtain an accurate resistance reading. It may take up to 30 minutes for the ECM to power down after the ignition key is removed. Removal of the ECM fuse, or the PCM/ETC fuse, allows the ECM to power down completely.
DTC P0451

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
Connector End View Reference:  Engine Control Module 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 
  1. Turn on the ignition, with the engine OFF.
  2. Monitor the Fuel Tank Pressure (FTP) sensor parameter voltage with the scan tool.
Is the voltage within the specified range?		 1.0-2.5 V Go to Step 3  Go to Step 4 
3
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 4  Go to Diagnostic Aids
4 
  1. Turn ON the ignition, with the engine OFF.
  2. Raise the vehicle. Refer to Lifting and Jacking the Vehicle .
  3. Disconnect the fuel tank in-line harness connector.
  4. Set up a DMM to test amperage.
  5. Measure the amperage from the 5-volt reference circuit of the FTP sensor to the engine control module (ECM) housing.
Is the amperage more than the specified value?		 80 mA Go to Step 5  Go to Step 7 
5 
  1. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the FTP sensor and the signal circuit of the FTP sensor.
  2. Observe the FTP voltage parameter, with a scan tool.
Is the voltage more than the specified value?		 4.8 V Go to Step 6  Go to Step 8 
6 
  1. Turn OFF the ignition.
  2. Remove the ECM fuse, or the PCM/ETC fuse, from the underhood electrical center.
    3. NOTE: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw.
  3. Measure the resistance from the low reference circuit of the FTP sensor to a good ground.
Is the resistance less than the specified value?		 5 Ω Go to Step 10  Go to Step 9 
7 Test the 5-volt reference circuit of the FTP sensor for high resistance between the harness connector and the control module. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
8 Test the signal circuit of the FTP sensor for high resistance between the harness connector and the control module. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
9 Test the low reference circuit of the FTP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
10
  1. Remove the fuel tank. Refer to Fuel Tank Replacement .
  2. Inspect the fuel tank wiring harness for the following conditions:
    • Damaged wiring
    • High resistance in the FTP harness from the fuel tank wiring harness connector to the FTP sensor
  3. Repair as necessary. Refer to Circuit Testing and Wiring Repairs .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 11 
11 Test for shorted terminals and for a poor connection at the FTP sensor harness connector, and the fuel tank harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 13 
12 Test for shorted terminals and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs .
Did you find and correct the condition?		 - Go to Step 15  Go to Step 14 
13 Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement .
Did you complete the replacement?		 - Go to Step 15  -
14 Replace the ECM. Refer to Control Module References for replacement, setup, and programming.
Did you complete the replacement?		 - Go to Step 15  -
15
  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.
Did the DTC fail this ignition?		 - Go to Step 2  Go to Step 16 
16 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 System OK
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