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DTC P0121: Throttle Position Sensor (main) Plausibility
 
 
 
 
TECHNICAL DESCRIPTION
Compare the actual measurement of volumetric efficiency by a mass airflow sensor signal with volumetric efficiency estimated from a throttle position sensor (main) signal.
 
 
MONITOR EXECUTION
Continuous
 
 
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC set in memory for the item monitored below)
  • Not applicable
Sensor (The sensor below is determined to be normal)
  • Not applicable
 
 
DTC SET CONDITIONS
Logic Flow Chart
Check Conditions
  • The difference between the actual volumetric efficiency and the volumetric efficiency estimated by the throttle position sensor (main) is 0 percent or more. Or, the volumetric efficiency is 60 percent or less.
  • Engine speed is 750 r/min or higher.
Judgment Criterion
  • For 0.4 second, the difference between the actual volumetric efficiency and the volumetric efficiency estimated by the throttle position sensor (main) is 33 percent or more.
  • For 0.4 second, the difference between the volumetric efficiency estimated by the throttle position sensor (main) and the volumetric efficiency estimated by the throttle position sensor (sub) is 8.8 percent or more.
Check Conditions
  • The difference between the actual manifold pressure and the manifold pressure estimated by the throttle position sensor (main) is 0 kPa (0 in.Hg) or more. Or, the manifold pressure is 73 kPa (21.6 in.Hg) or less.
  • Engine speed is 750 r/min or higher.
Judgment Criterion
  • For 0.4 second, the difference between the actual manifold pressure and the manifold pressure estimated by the throttle position sensor (main) is 40 kPa (11.8 in.Hg) or more.
  • For 0.4 second, the difference between the manifold pressure estimated by the throttle position sensor (main) and the manifold pressure estimated by the throttle position sensor (sub) is 7 kPa (2.1 in.Hg) or more.
 
 
FAIL-SAFE AND BACKUP FUNCTION
  • Throttle opening degree is restricted.
  • Throttle opening degree position is in default position if throttle position sensor (sub) fails.
 
 
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle Pattern 17 .
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Throttle position sensor (main) system failed.
  • Intake system vacuum leak.
  • There is some foreign matter around mass airflow sensor.
  • ECM failed.
 
 
 
DIAGNOSIS
Required Special Tools:
  • MB991958: Scan Tool (M.U.T.-III Sub Assembly)
    • MB991824: V.C.I.
    • MB991827: USB Cable
    • MB991910: Main Harness A
  • MB991658: Test Harness
STEP 1. Using scan tool MB991958, read the diagnostic trouble code (DTC).
cautionTo 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) Turn the ignition switch to the "ON" position.
(3) Read the DTC.
(4) Turn the ignition switch to the "LOCK" (OFF) position.
Is the diagnostic trouble code other than P0121 set?
Refer to, Diagnostic Trouble Code Chart .
Go to Step 2
 
STEP 2. Using scan tool MB991958, check data list item 13: Throttle Position Sensor (main).
(1) Detach the intake air hose at the throttle body.
(2) Disconnect the connector of the electronic-controlled throttle valve.
(3) Use test harness special tool (MB991658) to connect only terminals No. 3, No. 4, No. 5, and No. 6.
(4) Turn the ignition switch to the "ON" position.
(5) Set scan tool MB991958 to the data reading mode for item 13, Throttle Position Sensor (main).
  • Output voltage should be between 300 and 700 millivolts when the throttle valve is fully closed with your finger.
  • Output voltage should be 4,000 millivolts or more when the throttle valve is fully open with your finger.
(6) Turn the ignition switch to the "LOCK" (OFF) position.
Is the sensor operating properly?
Go to Step 3.
Refer to, DTC P0122 - Throttle Position Sensor (main) Circuit Low Input , DTC P0123 - Throttle Position Sensor (main) Circuit High Input .
 
STEP 3. Check for intake system vacuum leak.
Are there any abnormalities?
Repair it. Then go to Step 6.
Go to Step 4.
 
STEP 4. Check for foreign matter being around the mass airflow sensor.
Are there any foreign matter?
Repair it. Then go to Step 6.
Go to Step 5.
 
STEP 5. Check the trouble symptoms.
(1) Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle Pattern 17 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0121 set?
Replace the ECM (Refer to, Removal and Installation ). Then go to Step 6.
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 .
 
STEP 6. Test 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 17 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0121 set?
Retry the troubleshooting.
The inspection is complete.