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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 1387 (Engine Control System Diagnosis (DTC P0130 To DTC P0456) -- 1.8L (LV6)) >> Diagnosis >> DTC P0451 >> Test Description

Test Description

WARNING: This page is about a different car, the 2004 Pontiac Vibe. 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. 1:  The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
  2. 2:  This step determines if a FTP sensor malfunction is present. The input signal of the FTP sensor should indicate atmospheric pressure with the fuel tank filler cap removed. The fuel tank pressure sensor will vary with atmospheric pressure. A typical pressure at sea level is between 0.0-0.99 mm Hg (0.0-0.5 in H2O).
  3. 3:  This step determines if DTC P0451 is the result of a hard failure or an intermittent condition. Operating the vehicle in Check mode enhances the diagnostic capabilities of the PCM.
  4. 4:  This step determines if there is trapped negative or positive pressure at the FTP sensor.
  5. 6:  This step inspects for an open or a short in the FTP sensor 5-volt reference.
  6. 7:  This step inspects for excessive resistance in the reference voltage circuit. If the test lamp does not illuminate at all, there is resistance in the circuit.
  7. 9:  This step checks for an open or short in the FTP sensor input circuit.
  8. 11:  This step checks for an open in the FTP sensor ground circuit.
DTC P0451

Step Action Values Yes No
Schematic Reference:  Engine Controls Schematics 
1  Did you perform the Diagnostic System Check-Engine Controls? - Go to Step 2  Go to Diagnostic System Check - Engine Controls
2 
  1. Loosen the fuel tank filler cap in order to release any pressure inside the fuel tank.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the fuel tank pressure sensor (FTP) parameter on the scan tool.
Is the FTP sensor within the specified range?		 0.0-0.99 mm Hg (0.0-0.5 in H2O) Go to Step 3  Go to Step 4 
3 
  1. Perform the scan tool Clear DTC Information function.
  2. Place the vehicle into Check Mode using the scan tool. Refer to Service Bay Test .
  3. Operate the vehicle within the Freeze Frame conditions as noted.
Does the DTC P0451 set?		 - Go to Step 6  Go to Diagnostic Aids
4 
  1. Disconnect the vapor pressure supply hose to the FTP sensor.
  2. Turn ON the ignition, with the engine OFF.
  3. Observe the FTP sensor parameter on the scan tool.
Is the FTP sensor within the specified range?		 0.0-0.99 mm Hg (0.0-0.5 in H2O) Go to Step 5  Go to Step 6 
5 Repair the cause of the trapped vapor pressure in the fuel tank.
Is the action complete?		 - Go to Step 16  -
6 
  1. Turn OFF the ignition.
  2. Disconnect the FTP sensor electrical connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Use a DMM in order to measure the reference circuit voltage on the harness side of the FTP sensor connector.
Does the voltage equal the specified value?		 5 V Go to Step 7  Go to Step 8 
7 
  1. Connect a test lamp to the reference voltage circuit and ground.
  2. Turn ON the ignition, with the engine OFF.
Does the test lamp illuminate at least dimly?		 - Go to Step 9  Go to Step 14 
8 Repair the open in the reference voltage circuit of the FTP sensor between the sensor and SP108. Refer to Wiring Repairs in Wiring Systems.
Did you complete the repair?		 - Go to Step 16  -
9  Measure the voltage of the FTP sensor input circuit on the harness side using a DMM.
Is the voltage near the specified value?		 4.9 V Go to Step 11  Go to Step 10 
10
  1. Test the input circuit of the FTP sensor for high resistance.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.
Was a repair necessary?		 - Go to Step 16  Go to Step 15 
11  Probe the FTP sensor ground circuit on the harness side with a test lamp connected to B+.
Does the test lamp illuminate?		 - Go to Step 13  Go to Step 12 
12 Repair the open in the ground circuit of the FTP sensor between the sensor and SP108. Refer to Wiring Repairs in Wiring Systems.
Is the action complete?		 - Go to Step 16  -
13 Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement (FWD) or Fuel Tank Pressure Sensor Replacement (AWD) .
Is the action complete?		 - Go to Step 16  -
14 Repair the high resistance in the reference voltage circuit of the FTP sensor. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Did you complete the repair?		 - Go to Step 16  -
15 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .
Is the action complete?		 - Go to Step 16  -
16
  1. Use the scan tool in order to clear the DTCs.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC or until the EVAP test is complete. Review the supporting text.
Does the DTC run and pass?		 - Go to Step 17  Go to Step 2 
17 With a scan tool, observe the stored information, Capture Info.
Does the scan tool display any DTCs that you have not diagnosed?		 - Go to Diagnostic Trouble Code (DTC) List System OK
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