DTC P0451: Fuel Tank Differential Pressure Circuit Range/Performance Problem

CIRCUIT OPERATION

• The ECM (terminal No. 114) supplies a 5 volts reference signal to the fuel tank differential pressure sensor (terminal No. 3). The fuel tank differential pressure sensor (terminal No. 2) is grounded through the ECM (terminal No. 113).
  
• The fuel tank differential pressure sensor (terminal No. 1) returns a voltage signal to the ECM (terminal No. 112) that is proportional to the pressure in the fuel tank.
  

TECHNICAL DESCRIPTION

• The ECM monitors the fuel tank differential pressure sensor signal voltage.
  
• The ECM determines whether the fuel tank differential pressure sensor signal voltage is within normal operating parameters.
  

DESCRIPTIONS OF MONITOR METHODS

MONITOR EXECUTION

MONITOR EXECUTION CONDITIONS (OTHER MONITOR AND SENSOR)

• Evaporative emission purge solenoid monitor
  
• Evaporative emission ventilation solenoid monitor
  
• Fuel tank temperature sensor monitor
  
• Fuel level sensor monitor
  

• Mass airflow sensor
  
• Engine coolant temperature sensor
  
• Intake air temperature sensor
  
• Barometric pressure sensor
  
• Accelerator pedal position sensor
  

DTC SET CONDITIONS

Check Conditions

• Accelerator pedal is not depressed.
  
• Vehicle speed is less than 1.5 km/h (1 mph).
  

• If the voltage signal from the fuel tank differential pressure sensor changes by 0.2 volt or more, DTC P0451 will set. The code may also set if a sudden pressure fluctuation occurs 20 times while the engine is idling, and then 4 consecutive times during normal driving.
  

  note	If the number of sudden pressure fluctuations does not reach 20 during any one period of engine idling, or if the ignition switch is turned OFF, the counter will reset to 0.

  note	The conditions for deviating from idling operation are as follows: Vehicle speed is more than 50 km/h (31 mph).

FAIL-SAFE AND BACKUP FUNCTION

• None
  

OBD-ll DRIVE CYCLE PATTERN

TROUBLESHOOTING HINTS (THE MOST LIKELY CAUSES FOR THIS CODE TO BE SET ARE:)

• Fuel tank differential pressure sensor failed.
  
• Fuel tank differential pressure sensor circuit harness damage, or connector damage.
  
• ECM failed.
  

caution To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958. (1)Connect scan tool MB991958 to the data link connector.

(2)Plug the disconnected end of hose E. (3)Turn the ignition switch to the "ON" position. (4)Remove the fuel cap. (5)Set scan tool MB991958 to the data reading mode for item 52, Fuel Tank Differential Pressure Sensor. Output voltage should be between 1,500 and 3,500 millivolts.

(6)Connect the evaporative emission system pressure pump (Miller number 6872A) to the fuel tank filler tube by using fuel tank adapter (MLR-8382) and pressurize the fuel tank. The fuel tank pressure reading should increase. (7)Turn the ignition switch to the "LOCK" (OFF) position. Then disconnect scan tool MB991958. (8)Remove the evaporative emission system pressure pump (Miller number 6872A) and the fuel tank adapter (MLR-8382), and reinstall the fuel cap. (9)Connect hose E to the evaporative emission canister. Q. Is the sensor operating properly? It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How to Use Troubleshooting / Inspection Service Points - How to Cope with Intermittent Malfunctions . Go to Step 2 .

	Go to Step 3 .

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 12 .

(3)Measure the voltage between terminal No. 3 and ground by backprobing. Voltage should be between 4.9 and 5.1 volts. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage between 4.9 and 5.1 volts? Go to Step 6 . Go to Step 4 .

	Go to step 5 .

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 12 .

note Check harness after checking intermediate connector C-39. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 12 .

	Go to Step 11 .

	Repair it. Then go to Step 12 .

(3)Measure the voltage between terminal No. 2 and ground by backprobing. Voltage should be 0.5 volt or less. (4)Turn the ignition switch to the "LOCK" (OFF) position. Q. Is the measured voltage 0.5 volt or less? Go to Step 9 . Go to Step 7 .

	Go to Step 8 .

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 12 .

note Check harness after checking intermediate connector C-39. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 12 .

	Go to Step 11 .

	Repair it. Then go to Step 12 .

	Go to Step 10 .

	Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 12 .

note Check harness after checking intermediate connector C-39. If intermediate connector is damaged, repair or replace it. Refer to GROUP 00E, Harness Connector Inspection . Then go to Step 12 .

	Go to Step 11 .

	Repair it. Then go to Step 12 .

(2)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 15 .

	Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP 42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> . Then go to Step 12 .

	The inspection is complete.

(1)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 15 .

	Retry the troubleshooting.

	The inspection is complete.