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 JUDGEMENT

Check Conditions

Engine is running.
Air flow sensor is normal.

Judgement Criterion

The difference between volumetric efficiency (actual measurement) by the air flow sensor and volumetric efficiency estimated from the throttle position sensor (main) exceeds the specified value.

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
Failed engine-ECU

DIAGNOSIS PROCEDURE

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

Q. Is any other diagnosis code than P0121 stored?

	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 ).

Item 13: Throttle position sensor (main)

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 3.

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

Q. Is the check result normal?

	Replace the engine-ECU.

	Repair.