Part 1 of 2

DTC P0451: Evaporative Emission Control System Pressure Sensor Range/Performance

System Diagram:

Fuel Tank Differential Pressure Sensor Circuit Part 1:

Fuel Tank Differential Pressure Sensor Circuit Part 2:

CIRCUIT OPERATION
- The PCM (terminal 97) 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 PCM (terminal 96).
- The fuel tank differential pressure sensor (terminal 1) returns a voltage signal to the PCM (terminal 82) that is proportional to the pressure in the fuel tank.

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

DESCRIPTIONS OF MONITOR METHODS
- Detect malfunction if change of fuel tank differential pressure sensor output voltage during idling stays large during specified go/stop operations.

MONITOR EXECUTION
- Continuous.

MONITOR EXECUTION CONDITIONS (OTHER MONITOR AND SENSOR)

Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Evaporative emission purge solenoid monitor
- Evaporative emission ventilation solenoid monitor

Sensor (The sensors below are determined to be normal)
- Mass airflow sensor
- Barometric pressure sensor
- Intake air temperature sensor
- Engine coolant temperature sensor

Logic Flow Charts (Monitor Sequence):

LOGIC FLOW CHARTS (Monitor Sequence)

DTC SET CONDITIONS

Check Conditions
- Throttle valve is closed.
- Vehicle speed is 1.5 km/h (0.93 mph) or less.

Judgement 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 if the ignition switch is turned OFF, the counter will reset to zero.

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

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle Procedure 1 - Evaporative Emission System Leak Monitor. OBD-II Drive Cycle Pattern Lists

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 PCM.

OVERVIEW OF TROUBLESHOOTING
- DTC P0451 can be set by a faulty fuel tank differential pressure sensor or related circuit, or PCM failure.
- To check for system blockage, do a performance test which uses a mechanical vacuum gauge and scan tool MB991958 set on the fuel tank differential pressure sensor (TANK PRS SNSR 73). The mechanical gauge reading is used to verify scan tool MB991958 reading. A comparison of the mechanical gauge with the reading on scan tool MB991958 will locate a problem in the system.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: MUT-III USB Cable
- MB991911: MUT-III Main Harness B
- MB991658: Test Harness Set

STEP 1. Using scan tool MB991958, check data list item 73: Fuel Tank Differential Pressure Sensor.

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. Disconnect hose H from the evaporative emission canister, and plug the hose.
3. Turn the ignition switch to the "ON" position.
4. Remove the fuel cap.
5. Set scan tool MB991958 to the data reading mode.
- Item 73, Fuel Tank Differential Pressure Sensor.
- The fuel tank pressure reading on the scan tool should be -1.5 to 1.5 kPa (-0.443 to 0.443 in.Hg).

6. Connect an evaporative emission system pressure pump (Miller number 6872A) 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 MB991958.
8. Disconnect the evaporative emission system pressure pump, and reinstall the fuel cap.
9. Connect hose H to the canister.

Q: Is the fuel tank pressure between -1.5 and 1.5 kPa (-0.443 and 0.443 in.Hg)?

YES: It can be assumed that this malfunction is intermittent (Refer to How to Use Troubleshooting/Inspection Service Points - Intermittent Malfunction). Then go to Step 27.

NO: Go to Step 2.

STEP 2. Measure the signal voltage at intermediate connector D-17 by backprobing.

1. Disconnect hose H from the evaporative emission canister side, and plug the hose.
2. Remove the rear seat cushion (Refer to Rear Seat).
3. Pull up the carpet.
4. Turn the ignition switch to the "ON" position.
5. Remove the fuel cap.

6. Measure the voltage between connector D-17 terminal 11 and ground by backprobing.
- The measured voltage should be between 2.0 and 3.0 volts.

7. Connect an evaporative emission system pressure pump (Miller number 6872A) to the fuel filler neck and pressurize the fuel tank.
- The fuel tank pressure reading should increase.

8. Turn the ignition switch to the "LOCK" (OFF) position.
9. Disconnect the evaporative emission system pressure pump, and reinstall the fuel cap.
10. Connect hose H to the canister.

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

YES: Go to Step 3.

NO: Go to Step 7.

STEP 3. Measure the signal voltage at PCM connector C-112 by backprobing.

1. Do not disconnect PCM connector C-112.

2. Disconnect hose H from the evaporative emission canister side, and plug the hose.
3. Turn the ignition switch to the "ON" position.
4. Remove the fuel cap.

5. Measure the voltage between connector C-112 terminal 82 and ground by backprobing.
- The measured voltage should be between 2.0 and 3.0 volts.

STEP 4. Check PCM connector C-112 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 26.

NO: Repair or replace the damaged components. Refer to Harness Connector Inspection. Then go to Step 27.

STEP 5. Check intermediate connectors C-118, C-122, D-17 and PCM connector C-112 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 6.

NO: Repair or replace the faulty component. Refer to Harness Connector Inspection. Go to Step 27.

STEP 6. Check the harness wire between PCM connector C-112 terminal 82 and intermediate connector D-17 terminal 11 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. Then go to Step 27.

NO: Repair the damaged harness wire. Then go to Step 27.

STEP 7. Measure the 5-volt reference signal at intermediate connector D-17 by backprobing.

1. Do not disconnect intermediate connector D-17.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between connector D-17 terminal 9 and ground.
- The 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?

YES: Go to Step 11.

NO: Go to Step 8.

STEP 8. Measure the 5-volt reference signal at PCM connector C-111 by backprobing.

1. Do not disconnect PCM connector C-111.
2. Turn the ignition switch to the "ON" position.

3. Measure the voltage between connector C-111 terminal 97 and ground by backprobing.
- The measured 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?

YES: Go to Step 9.

NO: Go to Step 26

STEP 9. Check intermediate connectors C-103, C-118, C-122, and D-17 and PCM connector C-111 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 damaged components. Refer to Harness Connector Inspection. Then go to Step 27.

STEP 10. Check the harness wire between PCM connector C-111 terminal 97 and intermediate connector D-17 terminal 9 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. Then go to Step 27.

NO: Repair the damaged harness wire. Then go to Step 27.