P0451

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






















CIRCUIT OPERATION

- The ECM (terminal No. 114) supplies a 5-volt 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

- 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

- Fuel temperature sensor monitor

- Fuel level sensor monitor
Sensor (The sensors below are determined to be normal)

- Mass airflow sensor

- Barometric pressure sensor

- Intake air temperature sensor

- Engine coolant temperature sensor

- Accelerator pedal position sensor

DTC SET CONDITIONS

Logic Flow Chart






Check Conditions

- Accelerator pedal is not depressed.

- Vehicle speed is less than 1.5 km/h (1 mph).
NOTE:
The conditions for deviating from idling operation are as follows:

- Vehicle speed is more than 50 km/h (31 mph).

Judgement Criteria

- The drastic pressure fluctuation is detected 20 times or more per engine idling, which is that the fuel tank differential pressure sensor output voltage is 0.2 volt or more.

- The condition described above is consecutively detected 4 times under the normal driving conditions.
NOTE:
If the number of sudden pressure fluctuations does not reach 20 times during any one period of engine idling, or if the ignition switch is turned OFF, the counter will reset to 0.

OBD-II DRIVE CYCLE PATTERN

Refer to Diagnostic Function - OBD-II Drive Cycle - Pattern 16 Monitors, Trips, Drive Cycles and Readiness Codes.

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

- Connector damage.

- Harness damage.

- Fuel tank differential pressure sensor failed.

- ECM failed.

OVERVIEW OF TROUBLESHOOTING

- DTC P0451 can be set by a faulty fuel tank differential pressure sensor or related circuit, or ECM 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 (52: Fuel tank differential PRS. SNSR). 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 (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.

- MB991827: M.U.T.-III USB Cable

- MB991910: M.U.T.-III Main Harness A

- MB992110: Power Plant ECU Check Harness

STEP 1. Using scan tool MB991958, check data list item 52: 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 C 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 52, Fuel Tank Differential Pressure Sensor.
- The fuel tank pressure reading on the scan tool should be 1,500 to 3,500 mV.





(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 C to the evaporative emission canister.

Q. Is the fuel tank pressure between 1,500 and 3,500 mV?

YES It can be assumed that this malfunction is intermittent How to Cope With Intermittent Malfunctions).

NO Go to Step 2 .

STEP 2. Check harness connector B-11 at ECM and harness connector D-19 at fuel tank differential pressure sensor for damage.

Q. Is the harness connector in good condition?

YES Then go to Step 3 .
NO Repair or replace it. Harness Connector Inspection.
Then go to Step 7 .
STEP 3. Measure the 5-volt reference signal at fuel tank differential pressure sensor connector D-19.

(1)Remove the second seat assembly Second Seat Assembly Removal and Installation).





(2)Remove the floor inspection lid (LH).
(3)Disconnect fuel tank differential pressure sensor connector D-19.
(4)Turn the ignition switch to the "ON" position.





(5)Measure the voltage between terminal 3 and ground.

- The voltage should measure between 4.9 and 5.1 volts.
(6)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 5 .

NO Go to Step 4 .

STEP 4. Measure the 5-volt reference signal at ECM connector B-11 by using check harness special tool MB992110.





(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool MB992110 between the separated connectors.
(2)Turn the ignition switch to the "ON" position.
(3)Remove the fuel cap.





(4)Measure the voltage between terminal 114 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 Check harness connector C-129 at intermediate connector for damage, and repair or replace as required. Harness Connector Inspection.
If intermediate connector C-129 is in good condition, repair it because of harness damage fuel tank differential pressure sensor connector D-19 (terminal No. 3) and ECM connector B-11 (terminal No. 114). Then go to Step 7 .

NO Replace the ECM. When the ECM is replaced, register the ID code. Refer to ID registration procedure manual - ID codes registration judgement table [Vehicles with KOS] or ID registration procedure manual - ID codes registration judgement table [Vehicles with WCM]. Then go to Step 7 .

STEP 5. Check the harness wire between ECM connector B-11 and fuel tank differential pressure sensor connector D-19 for damage.

(1)Disconnect the connector B-11 and D-19 measure at the harness side.





(2)Measure the resistance between connector B-11 and connector D-19.
1. Connector B-11 (terminal No. 112) and connector D-19 (terminal No. 1).

2. Connector B-11 (terminal No. 113) and connector D-19 (terminal No. 2).

- Should be less than 2 ohms.

Q. Is the measured resistance less than 2 ohms?

YES Go to Step 6 .

NO Repair the damaged harness wires. Then go to Step 7 .

STEP 6. Replace the fuel tank differential pressure sensor.

(1)Replace the fuel tank differential pressure sensor.

(2)Carry out test drive with the drive cycle pattern. Refer to Diagnostic Function.
OBD-II Drive Cycle. Pattern 16 Monitors, Trips, Drive Cycles and Readiness Codes.

(3)Check the diagnostic trouble code (DTC).

Q. Is DTC P0451 set?

YES Replace the ECM. When the ECM is replaced, register the ID code. Refer to ID registration procedure manual - ID codes registration judgement table [Vehicles with KOS] or ID registration procedure manual - ID codes registration judgement table [Vehicles with WCM]. Then go to Step 7 .
NO The inspection is complete.
STEP 7. 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 - Pattern 16 Monitors, Trips, Drive Cycles and Readiness Codes.

(2)Check the diagnostic trouble code (DTC).

Q. Is DTC P0451 set?

YES Repeat the troubleshooting.
NO The procedure is complete.