Code No. P0122: Throttle Position Sensor Circuit Low Input

OPERATION

A power voltage of 5 V is applied to the throttle body assembly connector terminal from the engine-ECU connector terminal TPS5.
The power voltage is earthed to the engine-ECU connector terminal TPSE from the throttle body assembly connector terminal.
The sensor signal is inputted to the engine-ECU connector terminal TPSM from the throttle body assembly output terminal.

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.

FAIL-SAFE AND BACKUP FUNCTION

The throttle valve is opened. (Electrical discontinuity)
The DPF regeneration is prohibited.
The EGR control is stopped (fully closed).
The AS&G control is prohibited.

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 .

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. Perform voltage measurement at throttle body assembly connector.

Disconnect connector, and measure at harness side.
Ignition switch: ON
Voltage between terminal engine-ECU TPS5 line and body earth.

OK: 4.9 - 5.1 V

Q. Is the check result normal?

	Go to Step 5.

	Go to Step 3.

STEP 3. Check harness between throttle body assembly connector terminal and engine-ECU connector terminal TPS5.

Check power supply line for open/short circuit.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 4. M.U.T.-III data list

Refer to Data List Reference Table .

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.

STEP 5. Perform resistance measurement at throttle body assembly connector.

Disconnect connector, and measure at harness side.
Resistance between terminal engine-ECU TPSE line and body earth.

OK: Continuity (2 Ω or less)

Q. Is the check result normal?

	Go to Step 7.

	Go to Step 6.

STEP 6. Check harness between throttle body assembly connector terminal and engine-ECU connector terminal TPSE.

Check earthing line for damage.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 7. Perform voltage measurement at throttle body assembly connector.

Use special tool test harness (MB991658) to connect connector, and measure at pick-up harness.
Ignition switch: ON
Voltage between terminal engine-ECU TPSM line and body earth.

OK: 3.7 V or higher

Q. Is the check result normal?

	Go to Step 10.

	Go to Step 8.

STEP 8. Check harness between throttle body assembly connector terminal and engine-ECU connector terminal TPSM.

Check output line for short circuit.

Q. Is the check result normal?

	Go to Step 9.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 9. Check harness between throttle body assembly connector terminal and engine-ECU connector terminal TPS5.

Check power supply line for damage.

Q. Is the check result normal?

	Replace the throttle body assembly.

	Repair or replace the connector, or repair the damaged harness wire.

STEP 10. Check harness between throttle body assembly connector terminal and engine-ECU connector terminal TPSM.

Check output line for open circuit and damage.

Q. Is the check result normal?

	Go to Step 4.

	Repair or replace the connector, or repair the damaged harness wire.