P0121

DTC P0121: Throttle Position Sensor Circuit Range/Performance Problem

Throttle Position Sensor (TPS) Circuit:

CIRCUIT OPERATION
- A 5-volt power supply is applied on the throttle position sensor power terminal (terminal No. 1) from the ECM (terminal No. 81). The ground terminal (terminal No. 4) is grounded with ECM (terminal No. 92).
- When the throttle valve shaft is turned from the idle position to the fully opened position, the resistor between the throttle position sensor output terminal (terminal No. 2) and ground terminal will increase according to the rotation.

TECHNICAL DESCRIPTION
- The throttle position sensor outputs voltage which corresponds to the throttle valve opening angle.
- The ECM checks whether the voltage is within a specified range.

DESCRIPTIONS OF MONITOR METHODS
- Compare load value with throttle position sensor output voltage.

MONITOR EXECUTION
- Continuous

MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)

Other Monitor (There is no temporary DTC stored in memory for the item monitored)
- Not applicable

Sensor (The sensor is determined to be normal)
- Volume airflow sensor

DTC SET CONDITION

Logic Flow Chart:

Logic Flow Chart

Check Conditions
- 2 seconds or more have passed since the staring sequence was completed.
- Engine speed is higher than 2,000 r/min.
- Volumetric efficiency is higher than 60 percent.

Judgement Criteria
- Throttle position sensor output voltage has continued to be 0.8 volt or lower for 2 seconds.

DTC SET CONDITIONS

Logic Flow Chart:

Logic Flow Chart

Check Conditions
- 2 seconds or more have passed since the staring sequence was completed.
- Engine speed is lower than 3,000 r/min.
- Volumetric efficiency is lower than 30 percent.

Judgement Criteria
- Throttle position sensor output voltage has continued to be 4.6 volts or higher for 2 seconds.

OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 6 - Other Monitor. OBD-II Drive Cycle Pattern Lists

TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Throttle position sensor failed or incorrectly adjusted.
- Open throttle position sensor circuit, harness damage, or connector damage.
- ECM failed.

DIAGNOSIS

Required Special Tools:
- MB991958: Scan Tool (MUT-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991911: Main Harness B

STEP 1. Using scan tool MB991958, check data list item 14: Throttle Position Sensor.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.




1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991958 to the data reading mode for item 14, Throttle Position Sensor.
- With the throttle valve in the idle position, voltage should measure between 0.535 and 0.735 volt.
- With the throttle valve in the full-open position, voltage should measure between 4.5 and 5.0 volts.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points.

NO: Go to Step 2.




STEP 2.Check harness connector B-03 at throttle position sensor for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 3.

NO: Repair or replace it. Harness Connector Inspection. Then go to Step 14.

STEP 3. Check the throttle position sensor.




1. Disconnect connector B-03.




2. Measure the resistance between throttle position sensor side connector terminal No. 1 and No. 4.

Standard value: 3.5 - 6.5 kOhms

3. Measure resistance between the throttle position sensor side connector terminal No. 1 and No. 2.
4. Move the throttle valve from the idle position to the full-open position.
- Resistance should change smoothly in proportion to the opening angle of the throttle valve.

Q: Is the resistance normal?

YES: Go to Step 4.

NO: Replace the throttle position sensor. Throttle Body Assembly - Disassembly and Assembly. Then go to Step 14.

STEP 4. Measure the sensor supply voltage at throttle position sensor harness side connector B-03.




1. Disconnect connector B-03 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.




3. Measure the voltage between terminal No. 1 and ground.
- Voltage should measure between 4.8 and 5.2 volts.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the measured voltage between 4.8 and 5.2 volts?

YES: Go to Step 7.

NO: Go to Step 5.




STEP 5. Check harness connector C-115 at ECM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 6.

NO: Repair or replace it. Harness Connector Inspection. Then go to Step 14.







STEP 6. Check for harness damage between throttle position sensor connector B-03 (terminal No. 1) and ECM connector C-115 (terminal No. 81).

Q: Is the harness wire in good condition?

YES: Replace the ECM. Then go to Step 14.

NO: Repair it. Then go to Step 14.

STEP 7. Check for continuity at throttle position sensor harness side connector B-03.




1. Disconnect connector B-03 and measure at the harness side.




2. Measure the continuity between terminal No. 4 and ground.
- Should be less than 2 Ohms.

Q: Does continuity exist?

YES: Go to Step 10.

NO: Go to Step 8.




STEP 8. Check harness connector C-115 at ECM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 9.

NO: Repair or replace it. Harness Connector Inspection. Then go to Step 14.







STEP 9. Check for open circuit and harness damage between throttle position sensor connector B-03 (terminal No. 4) and ECM connector C-115 (terminal No. 92).

Q: Is the harness wire in good condition?

YES: Replace the ECM. Then go to Step 14.

NO: Repair it. Then go to Step 14.




STEP 10. Check harness connector C-115 at ECM for damage.

Q: Is the harness connector in good condition?

YES: Go to Step 11.

NO: Repair or replace it. Harness Connector Inspection. Then go to Step 14.







STEP 11. Check for harness damage between throttle position sensor connector B-03 (terminal No. 2) and ECM connector C-115 (terminal No. 84).

Q: Is the harness wire in good condition?

YES: Go to Step 12.

NO: Repair it. Then go to Step 14.

STEP 12. Check the incorrectly adjusted throttle position sensor. Throttle Position Sensor Adjustment.

Q: Is the output voltage normal?

YES: Go to Step 13.

NO: Adjust it. Then go to Step 14.

STEP 13. Using scan tool MB991958, check data list item 14:Throttle Position Sensor.

CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.




1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991958 to the data reading mode for item 14, Throttle Position Sensor.
- With the throttle valve in the idle position, voltage should measure between 0.535 and 0.735 volt.
- With the throttle valve in the full-open position, voltage should measure between 4.5 and 5.0 volts.

4. Turn the ignition switch to the "LOCK" (OFF) position.

Q: Is the sensor operating properly?

YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points.

NO: Replace the ECM. Then go to Step 14.

STEP 14. Perform the OBD-II drive cycle.

1. Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II Drive Cycle - Procedure 6 - Other Monitor. OBD-II Drive Cycle Pattern Lists
2. Check the diagnostic trouble code (DTC).

Q: Is DTC P0121 set?

YES: Repeat the troubleshooting.

NO: The procedure is complete.