P0451
DTC P0451: Evaporative Emission System Pressure Sensor Range/PerformanceSystem Diagram:
Fuel Tank Differential Pressure Sensor Circuit Part 1:
Fuel Tank Differential Pressure Sensor Circuit Part 2:
CIRCUIT OPERATION
- The ECM (terminal 81) supplies a 5-volts 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 92).
- The fuel tank differential pressure sensor (terminal 1) returns a voltage signal to the ECM (terminal 61) 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.
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.
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.
OVERVIEW OF TROUBLESHOOTING
- DTC P0451 can be set by a faulty fuel differential pressure sensor or related circuit, or ECM failure.
- To check a 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 to scan tool MB991958 determines the problem in the system.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: 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 I from the evaporative emission canister, and plug the hose.
3. Set scan tool MB991958 to the data reading mode for 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).
4. Connect an evaporative emission system pressure pump (Miller number 6872A) to the fuel tank filler tube and pressurize the fuel tank.
- The fuel tank pressure reading should increase.
5. Turn the ignition switch to the "LOCK" (OFF) position. Then disconnect scan tool MB991958.
6. Disconnect the evaporative emission system pressure pump, and reinstall the fuel cap.
7. Connect hose I 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. Go to Step 15.
NO: Go to Step 2.
STEP 2. Measure the signal voltage at fuel tank differential pressure sensor connector D-09.
1. Remove the rear seat assembly (Refer to Rear Seat).
2. Remove the floor pan access panel.
3. Use special tool Test Harness Set (MB991658) to connect terminals 1,2 and 3 of the fuel tank differential pressure sensor connector D-09.
4. Turn the ignition switch to the "ON" position.
5. Remove the fuel cap.
6. Measure the voltage between connector D-09 terminal 1 and ground.
- The measured voltage should measure between 2.0 to 3.0 volts.
7. 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 7.
STEP 3. Measure the signal voltage at ECM connector C-117 by backprobing.
1. Do not disconnect ECM connector C-117.
2. Turn the ignition switch to the "ON" position.
3. Remove the fuel cap.
4. Measure the voltage between connector C-117 terminal 61 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 4.
NO: Go to Step 5.
STEP 4. 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 I 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 for item 73, Fuel Tank Differential Pressure Sensor.
- The fuel tank pressure reading on the scan tool should be -1.5 to 1.5 kPa (-.443 to.443 in.Hg).
6. Connect an evaporative emission system pressure pump (Miller number 6872A) to the fuel tank filler tube and pressurize the fuel tank.
- The fuel tank pressure reading should increase.
7. Turn the ignition switch to the "LOCK" (OFF) position.
8. Disconnect the evaporative emission system pressure pump, and reinstall the fuel cap.
9. Connect hose I 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. Go to Step 15.
NO: Replace the ECM. Go to Step 15.
STEP 5. Check intermediate connectors C-113, C-122 and D-35, and ECM connector C-117, and fuel tank differential pressure sensor connector D-09 for loose, corroded or damaged terminals, or terminals pushed back in the connector.
Q: Are the connectors in good condition?
YES: Go to Step 6.
NO: Repair or replace the faulty components. Refer to Harness Connector Inspection. Go to Step 15.
STEP 6. Check the harness wire between ECM connector C-117 terminal 61 and intermediate connector D-09 terminal 1 for damage.
Q: Is the harness wire in good condition?
YES: This malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunction. Go to Step 15.
NO: Repair the damaged harness wire. Go to Step 15.
STEP 7. Measure the 5-volt reference signal at fuel tank differential pressure sensor connector D-09.
1. Disconnect fuel tank differential pressure sensor connector D-09.
2. Use special tool MB991658 to connect terminals 1, 2 and 3 of connector D-09.
3. Turn the ignition switch to the "ON" position.
4. Measure the voltage between terminal 3 and ground.
- The voltage should measure between 4.9 and 5.1 volts.
5. 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 8.
NO: Go to Step 11.
STEP 8. Measure the return circuit voltage at fuel tank differential pressure sensor connector D-09.
1. Disconnect fuel tank differential pressure sensor connector D-09.
2. Use special tool MB991658 to connect terminal 3 of connector D-09.
3. Turn the ignition switch to the "ON" position.
4. Measure the voltage between terminal 2 and ground.
- The voltage should measure 0.5 volt or less.
5. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the measure voltage 0.5 volt or less?
YES: Go to Step 9.
NO: Replace the fuel tank differential pressure sensor. Go to Step 15.
STEP 9. Check intermediate connectors C-113, C-122 and D-35, and ECM connector C-115,C-117 and fuel tank differential pressure sensor connector for D-09 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 damage components. Refer to Harness Connector Inspection. Go to Step 15.
STEP 10. Check the harness wire between ECM connector C-115 terminal 92 and fuel tank differential pressure sensor connector D-09 terminal 2 for damage.
Q: Is the harness wire in good condition?
YES: Replace the fuel tank differential pressure sensor. Go to Step 15.
NO: Repair or replace the harness wire. Go to Step 15.
STEP 11. Measure the 5-volts reference signal at ECM connector C-115 by backprobing.
1. Turn the ignition switch to the "ON" position.
2. Measure the voltage between connector C-115 terminal 81 and ground by backprobing.
- The measured voltage should measure between 4.9 and 5.1 volts.
3. 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 12.
NO: Go to Step 14.
STEP 12. Check intermediate connectors C-113, C-122 and D-35, and ECM connector C-115 and fuel tank differential pressure sensor connector for D-09 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 component. Go to Step 15.
STEP 13. Check the harness wire between ECM connector C-115 terminal 81 and fuel tank differential pressure sensor connector D-09 terminal 3 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 15.
NO: Repair or replace the harness wire. Go to Step 15.
STEP 14. Check ECM 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: Replace the ECM. Go to Step 15.
NO: Repair or replace the damaged components. Refer to Harness Connector Inspection. Go to Step 15.
STEP 15. Perform the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 1 - Evaporative Emission System Leak Monitor. OBD-II Drive Cycle Pattern Lists
2. Read the diagnostic trouble code (DTC).
Q: Is DTC P0451 set?
YES: Go to Step 2.
NO: The procedure is complete.