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 ).