Code No. P0122: Throttle Position Sensor Circuit Low Input




OPERATION



  • A power voltage of 5 V is applied to the electronic-controlled throttle valve (terminal No. 2) from the engine-ECU (terminal No. 80).
  • The power voltage is earthed to the engine-ECU (terminal No. 72) from the electronic-controlled throttle valve (terminal No. 4).
  • The sensor signal is inputted to the engine-ECU (terminal No. 124) from the electronic-controlled throttle valve output terminal (terminal No. 1).

FUNCTION



  • The throttle position sensor converts the throttle valve position into voltage and inputs it into the engine-ECU.
  • The engine-ECU control the throttle valve position.

TROUBLE JUDGMENT


Check Conditions
  • Battery positive voltage is 8 - 16 V
  • 2 seconds later after the ignition switch has been in "ON" position or the engine has started up
Judgment Criterion
  • The throttle position sensor output voltage is 0.15 V or less for 0.5 second.

PROBABLE CAUSES



  • Failed throttle position sensor
  • Open/short circuit in throttle position sensor circuit or loose connector contact
  • Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-III data list

  • Refer to Data List Reference Table .

  1. Item 45: Throttle position sensor

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Go to Step 2 .

STEP 2. Connector check: A-132 electronic-controlled throttle valve connector

Q. Is the check result normal?

Go to Step 3 .

Repair or replace the connector.

STEP 3. Perform voltage measurement at A-132 electronic-controlled throttle valve connector.


  • Disconnect connector, and measure at harness side.
  • Ignition switch: ON
  • Voltage between terminal No. 2 and earth.
OK: 4.9 - 5.1 V

Q. Is the check result normal?

Go to Step 7 .

Go to Step 4 .

STEP 4. Connector check: C-105 engine-ECU connector

Q. Is the check result normal?

Go to Step 5 .

Repair or replace the connector.

STEP 5. Check harness between A-132 (terminal No. 2) electronic-controlled throttle valve connector and C-105 (terminal No. 80) engine-ECU connector.



  • Check power supply line for open/short circuit.

Q. Is the check result normal?

Go to Step 6 .

Repair the damaged harness wire.

STEP 6. M.U.T.-III data list

  • Refer to Data List Reference Table .

  1. Item 45: Throttle position sensor

Q. Is the check result normal?
Intermittent malfunction (Refer to GROUP 00 - How to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent Malfunctions ).
Replace the engine-ECU. When the engine-ECU is replaced, write the chassis number (Refer to GROUP 00 - How to Perform Chassis Number Writing ). After replacing the engine-ECU, register the injector identification code and learn fuel injection (Refer to GROUP 00 - Precautions Before Service - What The Common Rail Engine Learns ).

STEP 7. Perform resistance measurement at A-132 electronic-controlled throttle valve connector.


  • Disconnect connector, and measure at harness side.
  • Resistance between terminal No. 4 and earth.
OK: Continuity (2 Ω or less)

Q. Is the check result normal?

Go to Step 10 .

Go to Step 8 .

STEP 8. Connector check: C-105 engine-ECU connector

Q. Is the check result normal?

Go to Step 9 .

Repair or replace the connector.

STEP 9. Check harness between A-132 (terminal No. 4) electronic-controlled throttle valve connector and C-105 (terminal No. 72) engine-ECU connector.



  • Check earthing line for damage.

Q. Is the check result normal?

Go to Step 6 .

Repair the damaged harness wire.

STEP 10. Connector check: C-105 engine-ECU connector

Q. Is the check result normal?

Go to Step 11 .

Repair or replace the connector.

STEP 11. Perform voltage measurement at A-132 electronic-controlled throttle valve connector.


  • Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
  • Ignition switch: ON
  • Voltage between terminal No. 1 and earth.
OK: 3.7 V or higher.

Q. Is the check result normal?

Go to Step 15 .

Go to Step 12 .

STEP 12. Connector check: C-103 engine-ECU connector.

Q. Is the check result normal?

Go to Step 13 .

Repair or replace the connector.

STEP 13. Check harness between A-132 (terminal No. 1) electronic-controlled throttle valve connector and C-103 (terminal No. 124) engine-ECU connector.



  • Check output line for short circuit.

Q. Is the check result normal?

Go to Step 14 .

Repair the damaged harness wire.

STEP 14. Check harness between A-132 (terminal No. 2) electronic-controlled throttle valve connector and C-105 (terminal No. 80) engine-ECU connector.



  • Check power supply line for damage.

Q. Is the check result normal?

Replace the electronic-controlled throttle valve.

Repair the damaged harness wire.

STEP 15. Check harness between A-132 (terminal No. 1) electronic-controlled throttle valve connector and C-103 (terminal No. 124) engine-ECU connector.



  • Check output line for open circuit and damage.

Q. Is the check result normal?

Go to Step 6 .

Repair the damaged harness wire.