Code No. P0121: Trustful Check Throttle Position Sensor (main)


FUNCTION



  • Compare the actual measurement of volumetric efficiency by an air flow sensor signal with volumetric efficiency estimated from a throttle position sensor (main) signal.

TROUBLE JUDGMENT


Check Conditions
  • Difference between the actual volumetric efficiency and the volumetric efficiency estimated by the throttle position sensor (main) is more than 0 %. Or, the volumetric efficiency is less than 60 %.
  • Engine speed is more than 750 r/min and is less than 3,000r/min. Or, the throttle position sensor (main) output voltage is less than 3 V.
Judgement Criterion
  • Difference between the actual volumetric efficiency and the volumetric efficiency estimated by the throttle position sensor (main) is more than 33 %.

FAIL-SAFE AND BACKUP FUNCTION



  • Throttle opening degree is restricted.
  • Throttle opening degree position is in default position if throttle position sensor (sub) fails.

PROBABLE CAUSES



  • Failed throttle position sensor (main)
  • Harness damage in throttle position sensor (main) circuit or loose connector contact
  • Failed intake air system
  • There is some foreign matter around air flow sensor
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III diagnosis code

Q. Is any other diagnosis code than P0121 set?
Inspection chart for diagnosis code (Refer to ).
Go to Step 2 .

STEP 2. M.U.T.-III data list

  • Data list reference table (Refer to ).

  1. Item 13: Throttle position sensor (main)

Q. Is the check result normal?
Go to Step 3 .
Check throttle position sensor (main) system. Check code No. P0122: throttle position sensor (main) circuit low input (Refer to ). Check code No. P0123: throttle position sensor (main) circuit high input (Refer to ).

STEP 3. Check air intake from inlet hose and inlet manifold.

Q. Is the check result normal?
Go to Step 4 .
Repair.

STEP 4. Check air flow sensor.

  • Check that there is not foreign matter around air flow sensor.

Q. Is the check result normal?
Go to Step 5 .
Repair.

STEP 5. M.U.T.-III diagnosis code

  • Reconfirmation of diagnosis code.

Q. Is diagnosis code set?
Replace the engine-ECU.
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).