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Home >> Cadillac >> 2005 >> CTS Base, 2.8 T, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - 2.8L (DTC P0420 To P1551) >> Engine Controls Diagnosis >> DTC P0451 >> Test Description

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. 3:  A large leak in the evaporative emission (EVAP) system could cause this DTC to set. Inspect the entire EVAP system for damaged, loose, or leaking EVAP pipes, hoses, or components. Refer to DTC P0451  if you suspect a leak.
  3. 5:  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.
  4. 6:  This step tests the signal circuit of the FTP sensor.
P0451 Fuel Tank Pressure (FTP) Sensor Performance

Step Action Values Yes No
Schematic Reference:  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 in Vehicle DTC Information
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 5 
3 
  1. Inspect the EVAP system for the following conditions:
    • A loose, missing, or damaged service port Schrader valve
    • A loose, incorrect, missing, or damaged fuel fill cap
    • A damaged EVAP purge solenoid
  2. Raise the vehicle on a hoist. Refer to Lifting and Jacking the Vehicle in General Information.
  3. Inspect the EVAP system for the following conditions:
    • Disconnected, incorrectly routed, kinked, or damaged EVAP pipes and hoses
    • A damaged EVAP vent valve or EVAP canister
Did you find and correct the condition?		 - Go to Step 15  Go to Step 4 
4
  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 5  Go to Diagnostic Aids
5 
  1. Turn ON the ignition, with the engine OFF.
  2. Raise the vehicle. Refer to Lifting and Jacking the Vehicle in General Information.
  3. Disconnect the FTP sensor connector at the evaporative emission (EVAP) canister.
  4. Set-up a DMM to test amperage on the 400 mA scale.
  5. Measure the amperage from the 5-volt reference circuit of the FTP sensor to a good ground.
Is the amperage more than the specified value?		 80 mA Go to Step 6  Go to Step 8 
6 
  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 Sensor voltage parameter, with a scan tool.
Is the voltage more than the specified value?		 4.8 V Go to Step 7  Go to Step 9 
7
  1. Turn OFF the ignition.
  2. Remove the ECM/TCM 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 11  Go to Step 10 
8 Test the 5-volt reference circuit of the FTP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
9 Test the signal circuit of the FTP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
10 Test the low reference circuit of the FTP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.
Did you find and correct the condition?		 - Go to Step 15  Go to Step 12 
11 Test for shorted terminals and for a poor connection at the FTP sensor harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
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 engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.
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 in Computer/Integrating Systems 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 in Vehicle DTC Information System OK
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