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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 the 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 higher than 0 percent. Or, the volumetric efficiency is 60 percent or lower.
  • Engine speed is 750 r/min or higher.
Judgment Criteria
  • For 0.4 second, the difference between the actual volumetric efficiency and the volumetric efficiency estimated by the throttle position sensor (main) is higher than 33 percent.
  • 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 higher.
Check Conditions
  • The difference between the actual manifold pressure and the manifold pressure estimated by the throttle position sensor (main) is more than 0 kPa (0 in.Hg). 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 more than 40 kPa (11.8 in.Hg).
  • 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 1 .
 
 
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
STEP 1. Using scan tool (M.U.T.-IIISE), read the diagnostic trouble code (DTC).
cautionTo prevent damage to scan tool (M.U.T.-IIISE), always turn off the power supply mode of the electric motor switch before connecting or disconnecting scan tool (M.U.T.-IIISE).
(1) Connect scan tool (M.U.T.-IIISE). Refer to HOW TO CONNECT THE SCAN TOOL (M.U.T.-IIISE) .
(2) Turn on the power supply mode of the electric motor switch.
(3) Read the DTC.
(4) Turn off the power supply mode of the electric motor switch.
Is the diagnostic trouble code other than P0121 set?
Refer to Diagnostic Trouble Code Chart .
Go to Step 2.
 
STEP 2. Using scan tool (M.U.T.-IIISE), 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 throttle body assembly.
(3) Use test harness special tool MB991658 to connect only terminals TPSE, TPSM, TPS5 and TPSS line.
(4) Operate the electric motor switch without depressing the brake pedal and turn ON (not READY) the power supply mode of electric motor switch.
(5) Set scan tool (M.U.T.-IIISE) 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 between 4,400 and 4,800 millivolts when the throttle valve is fully open with your finger.
(6) Turn off the power supply mode of the electric motor switch.
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 1 .
(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 1 .
(2) Check the diagnostic trouble code (DTC).
Is DTC P0121 set?
Retry the troubleshooting.
The inspection is complete.