P0451

System Diagram:

Fuel Tank Differential Pressure Sensor Circuit:

Connectors:

CIRCUIT OPERATION
- The ECM (terminal 42) or PCM (terminal 46) supplies a 5-volt reference signal to the fuel tank differential pressure sensor (terminal 3). The fuel tank differential pressure sensor (terminal 2) is grounded through the ECM (terminal 49) or PCM (terminal 57) . The fuel tank differential pressure sensor (terminal 1) returns a voltage signal to the ECM (terminal 93) or PCM (terminal 92) that is proportional to the pressure in the fuel tank.

TECHNICAL DESCRIPTION
- The ECM or PCM monitors the fuel tank differential pressure sensor output voltage.
- The ECM or PCM determines whether the fuel tank differential pressure sensor signal voltage is within normal operating parameters.

DTC SET CONDITIONS

Test Conditions:
- Throttle valve is closed.
- Vehicle speed is less than 1.5 km/h (0.93 mph).

Judgment Criteria:
- 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 twenty times while the engine is idling, and then eight consecutive times during normal driving.

NOTE: If the number of sudden pressure fluctuations does not reach twenty during any one period of engine idling, or the ignition switch is turned "LOCK" (OFF) position, the counter will reset to zero.

NOTE: The conditions for deviating from idling operation are as follows:
- Engine speed is greater than 2,500 rpm.
- Vehicle speed is greater than 15 km/h (9.3 mph).
- Volumetric efficiency is greater than 55 percent.

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Malfunction of the fuel tank differential pressure sensor.
- A damaged harness in the fuel tank differential pressure sensor circuit.
- Malfunction of the ECM or PCM .

OVERVIEW OF TROUBLESHOOTING
- DTC P0451 can be set by a faulty fuel tank differential pressure sensor or related circuit, or ECM or PCM failure.
- To check a system blockage, do a performance test which uses a mechanical vacuum gauge and scan tool MB991502 set on the fuel tank differential pressure sensor (TANK PRS SNSR 73).
The mechanical gauge reading is used to verify scan tool MB991502 reading.
A comparison of the mechanical gauge with the reading on scan tool MB991502 will locate a problem in the system.

DIAGNOSIS

Required Special Tools:
- MB991502: Scan Tool (MUT-II)
- MB991658: Test Harness Set
- MB991709: Test Harness Set

STEP 1. Using scan tool MB991502, check data list item 73: Fuel Tank Differential Pressure Sensor.

CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

1. Connect scan tool MB991502 t6the data link connector.
2. Disconnect hose I at the evaporative emission canister side and plug the hose I securely.
3. Turn the ignition switch to the "ON" position.
4. Remove the fuel cap.
5. Set scan tool MB991502 to the data reading mode for item 73, Fuel Tank Differential Pressure Sensor.
- The fuel tank pressures reading on the scan tool should be -3.3 to 3.3 kPa (-0.97 to 0.97 inHg).
6. Connect an evaporative emission system pressure pump to the fuel filler neck 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 MB991502.

Q: Is the fuel tank pressure between -3.3 and 3.3 kPa (-0.97 and 0.97 inHg)?

YES: It can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). Go to Step 23.
NO: Go to Step 2.

STEP 2. Measure the signal voltage at intermediate connector D-16.

1. Remove the rear seat cushion. (Refer to Rear Seat P.23C-46).
2. Remove the floor pan access panel.
3. Disconnect intermediate connector D-16.
4. Connect special tools MB991658 and MB991709 between intermediate connector D-16 terminals 5, 6 and 8.
5. Turn the ignition switch to the "ON" position.
6. Remove the fuel cap.
7. Measure the voltage between intermediate connector D-16 terminal 5 and ground.
- The measured voltage should measure between 2.0 and 3.0 volts.
8. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 2.0 and 3.0 volts?

YES: Go to Step 3.
NO: Go to Step 6.

STEP 3. Measure the signal voltage at ECM connector C-122 or PCM connector C-119 by backprobing.

1. Do not disconnect the ECM connector C-122 or PCM connector C-119 .
2. Turn the ignition switch to the "ON" position.
3. Remove the fuel cap.
4. Measure the voltage between ECM connector C-122 terminal 93 or PCM connector C-119 terminal 92 and ground by backprobing.
- The measured voltage should measure between 2.0 and 3.0 volts.
5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 2.0 and 3.0 volts?

YES: Go to Step 22.
NO: Go to Step 4.

Connectors:

Connectors:

STEP 4. Check intermediate connectors C-25, C-210 and D16, and ECM connector C-122 or PCM connector C-119 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connectors and terminals in good condition?

YES: Go to Step 5.
NO: Repair or replace the faulty components. (Refer to Harness Connector Inspection) Go to Step 23.

Connectors:

STEP 5. Check the harness wires between ECM connector C-122 terminal 93 or PCM connector C-119 terminal 92 and intermediate connector D-16 terminal 5 for damage.

Q: Are the harness wires in good condition?

YES: It can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). Go to Step 23.
NO: Repair the damaged harness wires. Go to Step 23.

Connectors:

STEP 6. Measure the 5-volt reference signal at intermediate connector D-16.

1. Disconnect intermediate connector D-16.
2. Connect special tools MB991658 and MB991709 between intermediate connector D-16 terminals 5, 6 and 8.
3. Turn the ignition switch to the "ON" position.
4. Measure the voltage between intermediate connector D-16 terminal 8 and ground.
- The measured voltage should measure between 4.8 and 5.2 volts.
5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 4.8 and 5.2 volts?

YES: Go to Step 11.
NO: Go to Step 7.

STEP 7. Measure the 5-volt reference signal at ECM connector C-118 or PCM connector C-115 by backprobing.

1. Do not disconnect ECM connector C-118 or PCM connector C-115 .
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between ECM connector C-118 terminal 42 or PCM connector C-115 terminal 46 and ground by backprobing.
- The measured voltage should measure between 4.8 and 5.2 volts.
4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 4.8 and 5.2 volts?

YES: Go to Step 9.
NO: Go to Step 8.

STEP 8. Check ECM connector C-118 or PCM connector C-115 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connector and terminals in good condition?

YES: Go to Step 22.
NO: Repair or replace the faulty component. (Refer to Harness Connector Inspection). Go to Step 23.

Connectors:

STEP 9. Check intermediate connectors C-25, C-210 and D-16 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connectors and terminals in good condition?

YES: Go to Step 10.
NO: Repair or replace the faulty components. (Refer to Harness Connector Inspection). Go to Step 23.

STEP 10. Check the harness wires between ECM connector C-118 terminal 42 or PCM connector C- 115 terminal 46 and intermediate connector D-16 terminal 8 for damage.

Q: Are the harness wires in good condition?

YES: It can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). Go to Step 23.
NO: Repair the damaged harness wires. Go to Step 23.

STEP 11. Measure the fuel tank differential pressure sensor return voltage at intermediate connector D-16.

1. Disconnect intermediate connector D-16.
2. Connect special tools MB991658 and MB991709 between intermediate connector D-16 terminals 5 and 8.
3. Turn the ignition switch to the "ON" position.
4. Measure the voltage at the intermediate connector D-16 male side connector between terminal 6 and ground.
- The measured voltage should measure between 4.8 and 5.2 volts.
5. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 0.5 and 4.8 volts?

YES: Go to Step 12.
NO: Go to Step 15.

Connectors:

Connectors:

STEP 12. Check intermediate connectors C-25, C-210 and D-16, and ECM connector C-118 or PCM connector C-115 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connectors and terminals in good condition?

YES: Go to Step 13.
NO: Repair or replace the faulty components. (Refer to Harness Connector Inspection). Go to Step 23.

Connectors:

STEP 13. Check the harness wires between ECM connector C-118 terminal 49 or PCM connector C- 115 terminal 57 and intermediate connector D-16 terminal 6 for damage.

Q: Are the harness wires in good condition?

YES: Go to Step 14.
NO: Repair the damaged harness wires. Go to Step 23.

STEP 14. Measure the fuel tank differential pressure sensor ground voltage at ECM connector C-118 or PCM connector C-115 by backprobing.

1. Do not disconnect ECM connector C-118 or PCM connector C-115 .
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between ECM connector C-118 terminal 49 or PCM connector C-115 terminal 57 and ground by backprobing.
- The measured voltage should measure 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?

YES: Go to Step 19.
NO: Go to Step 22.

Connectors:

STEP 15. Check intermediate connector D-16 and fuel tank differential pressure sensor connector D-18 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connectors and terminals in good condition?

YES: Go to Step 16.
NO: Repair or replace the faulty components. (Refer to Harness Connector Inspection). Go to Step 23.

Connectors:

STEP 16. Check the harness wire between intermediate connector D-16 terminal 8 and fuel tank differential pressure sensor connector D-18 terminal 3 for damage.

Q: Is the harness wire in good condition?

YES: Go to Step 17.
NO: Repair the damaged harness wire. Go to Step 23.

Connectors:

STEP 17. Check the harness wire between intermediate connector D-16 terminal 6 and fuel tank differential pressure sensor connector D-18 terminal 2 for damage.

Q: Is the harness wire in good condition?

YES: Go to Step 18.
NO: Repair the damaged harness wire. Go to Step 23.

STEP 18. Measure the fuel tank differential pressure sensor ground voltage at fuel tank differential pressure connector D-18.

1. Remove the center exhaust pipe. (Refer to Exhaust Pipe, Main Muffler and Catalytic Converter).
2. Remove the fuel tank band assembly (Refer to Fuel Tank), and tilt the fuel tank.
3. Disconnect fuel tank differential pressure sensor connector D-18.
4. Connect special tool MB991658 to both halves of connector D-18 terminal 1.
5. Turn the ignition switch to the "ON" position.
6. Remove the fuel cap.
7. Measure the voltage between fuel tank differential pressure sensor side connector D-18 terminal 2 and ground.
- The measured voltage should measure between 0.5 and 4.8 volts.
8. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 0.5 and 4.8 volts?

YES: It can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). Go to Step 23.
NO: Replace the fuel tank differential pressure sensor. (Refer to Fuel Tank). Go to Step 23.

STEP 19. Measure the signal voltage at fuel tank differential pressure connector D-18.

1. Remove the center exhaust pipe. (Refer to Exhaust Pipe, Main Muffler and Catalytic Converter).
2. Remove the fuel tank band assembly (Refer to Fuel Tank), and tilt the fuel tank.
3. Disconnect fuel tank differential pressure sensor connector D-18.
4. Connect special tool MB991658 to both halves of connector D-18.
5. Turn the ignition switch to the "ON" position.
6. Remove the fuel cap.
7. Measure the voltage between fuel tank differential pressure sensor connector D-18 terminal 1 and ground.
- The measured voltage should measure between 2.0 and 3.0 volts.
8. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 2.0 and 3.0 volts?

YES: Go to Step 20.
NO: Replace the fuel tank differential pressure sensor. (Refer to Fuel Tank). Go to Step 23.

Connectors:

STEP 20. Check intermediate connector D-16 and fuel tank differential pressure sensor connector D-18 for loose, corroded or damaged terminals, or terminals pushed back in the connector.

Q: Are the connectors and terminals in good condition?

YES: Go to Step 21.
NO: Repair or replace the faulty components. (Refer to Harness Connector Inspection). Go to Step 23.

Connectors:

STEP 21. Check the harness wire between intermediate connector D-16 terminal 5 and fuel tank differential pressure sensor connector D-18 terminal 1 for damage.

Q: Is the harness wire in good condition?

YES: It can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). Go to Step 23.
NO: Repair the damaged harness wire. Go to Step 23.

STEP 22. Using scan tool MB991502, check data list item 73: Fuel Tank Differential Pressure Sensor.

CAUTION
To prevent damage to scan tool MB991502 always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.

1. Connect scan tool MB991502 to the data link connector.
2. Disconnect hose I at the evaporative emission canister side and plug the hose I securely.
3. Turn the ignition switch to the "ON" position.
4. Remove the fuel cap.
5. Set scan tool MB991502 to the data reading mode for item 73 Fuel Tank Differential Pressure Sensor.
- The fuel tank pressures reading on the scan tool should be -3.3 to 3.3 kPa (-0.97 to 0.97 inHg).
6. Connect an evaporative emission system pressure pump to the fuel filler neck 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 MB991502.

Q: Is the fuel tank pressure between -3.3 and 3.3 kPa (-0.97 and 0.97 inHg)?

YES: It can be assumed that this malfunction is intermittent. (Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction). Go to Step 23.
NO: Replace the ECM or PCM . Go to Step 23.

STEP 23. Perform the OBD-III drive cycle.

1. Carry out a test drive with the drive cycle pattern. [Refer to Trouble Code Diagnosis - OBD-III Drive Cycle (Procedure 1: Evaporative Emission Control system Leak Monitor).
2. Read the diagnostic trouble code (DTC).

Q: Is DTC P0451 set?

YES: Go to Step 2.
NO: The procedure is complete.