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. 93).
  • The power voltage is earthed to the engine-ECU (terminal No. 34) from the electronic-controlled throttle valve (terminal No. 4).
  • The sensor signal is inputted to the engine-ECU (terminal No. 40) 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.

PROBABLE CAUSES



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

DIAGNOSTIC 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: B-31 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 B-31 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: D-213 engine-ECU connector

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

STEP 5. Check harness between B-31 (terminal No. 2) electronic-controlled throttle valve connector and D-213 (terminal No. 93) 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 - Precautions Before Service - 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 ). After registering the injector identification code, the vehicle equipped with the closed type DPF carries out the forcible DPF regeneration. (Refer to GROUP 17 - Diesel Particulate Filter (DPF) System - Forcible DPF Regeneration ).

STEP 7. Perform resistance measurement at B-31 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: D-213 engine-ECU connector

Q. Is the check result normal?
Go to Step 9 .
Repair or replace the connector.

STEP 9. Check harness between B-31 (terminal No. 4) electronic-controlled throttle valve connector and D-213 (terminal No. 34) 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: D-213 engine-ECU connector

Q. Is the check result normal?
Go to Step 11 .
Repair or replace the connector.

STEP 11. Perform voltage measurement at B-31 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: D-213 engine-ECU connector.

Q. Is the check result normal?
Go to Step 13 .
Repair or replace the connector.

STEP 13. Check harness between B-31 (terminal No. 1) electronic-controlled throttle valve connector and D-213 (terminal No. 40) 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 B-31 (terminal No. 2) electronic-controlled throttle valve connector and D-213 (terminal No. 93) 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 B-31 (terminal No. 1) electronic-controlled throttle valve connector and D-213 (terminal No. 40) 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.