P0121
P0121 - Throttle Position Sensor 1 Performance, 4.0L
For wiring diagrams, refer to.
• When Monitored: With the engine running and no TPS or MAP sensor DTCs present.
• Set Condition: The PCM detects that the input voltage is not within a specified range based on operating conditions.
• Always perform the pre-diagnostic troubleshooting procedure before proceeding. Refer to => Non-DTC Based Diagnostics. Pre-Diagnostic Troubleshooting Procedure
Test Step 1 - DTC is Active
• Diagnose and repair any throttle body circuit, system voltage, or sensor supply voltage DTCs before continuing with this test.
• Start the engine and allow it to reach operating temperature.
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
• With the scan tool select view DTCs.
• If the DTC does not reset it may be necessary to test drive the vehicle.
Is the status Active for this DTC?
Yes
• Go to Test Step 2 => [ Test
Step 2 - Excessive Resistance in the 5 Volt Supply Circuit ]
No
• Refer to the checking for an intermittent DTC diagnostic procedure. Refer to => Non-DTC Based Diagnostics. Checking for an Intermittent DTC
Test Step 2 - Excessive Resistance in the 5 Volt Supply Circuit
• Turn the ignition OFF.
Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals, resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
• Using a voltmeter, perform a voltage drop test by backprobing the 5 volt supply circuit at the throttle body harness connector and probing the appropriate terminal of special tool #8815. Make sure the voltmeter leads are connected so that positive polarity is displayed on the voltmeter.
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
• Start the engine.
Is the voltage less than 0.5 volts?
Yes
• Go to Test Step 3 => [ Test
Step 3 - Excessive Resistance in the TP Signal 1 Circuit ]
No
• Repair the excessive resistance in the 5 volt supply circuit.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
Test Step 3 - Excessive Resistance in the TP Signal 1 Circuit
• Turn the ignition OFF.
Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals, resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
• Using a voltmeter, perform a voltage drop test by backprobing the TP signal 1 circuit at the throttle body harness connector and probing the appropriate terminal of special tool #8815. Make sure the voltmeter leads are connected so that positive polarity is displayed on the voltmeter.
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
• Start the engine.
Is the voltage less than 0.5 volts?
Yes
• Go to Test Step 4 => [ Test
Step 4 - Excessive Resistance in the TP Signal 2 Circuit ]
No
• Repair the excessive resistance in the TP signal 1 circuit.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
Test Step 4 - Excessive Resistance in the TP Signal 2 Circuit
• Turn the ignition OFF.
Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals, resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
• Using a voltmeter, perform a voltage drop test by backprobing the TP signal 2 circuit at the throttle body harness connector and probing the appropriate terminal of special tool #8815. Make sure the voltmeter leads are connected so that positive polarity is displayed on the voltmeter.
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
• Start the engine.
Is the voltage less than 0.5 volts?
Yes
• Go to Test Step 5 => [ Test
Step 5 - Excessive Resistance in the TP Sensor Ground Circuit ]
No
• Repair the excessive resistance in the TP signal 2 circuit.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
Test Step 5 - Excessive Resistance in the TP Sensor Ground Circuit
• Turn the ignition OFF.
Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals, resulting in poor terminal to pin connection. Install Miller Special Tool #8815 to perform diagnosis.
• Using a voltmeter, perform a voltage drop test by backprobing the TP sensor ground circuit at the throttle body harness connector and probing the appropriate terminal of special tool #8815. Make sure the voltmeter leads are connected so that positive polarity is displayed on the voltmeter.
When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts, or fan. Do not wear loose clothing. Failure to follow these instructions can result in personal injury or death.
• Start the engine.
Is the voltage less than 0.5 volts?
Yes
• Go to Test Step 6 => [ Test
Step 6 - TP Signal 1 Circuit Shorted to the TP Signal 2 Circuit ]
No
• Repair the excessive resistance in the TP sensor ground circuit.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
Test Step 6 - TP Signal 1 Circuit Shorted to the TP Signal 2 Circuit
• Turn the ignition OFF.
• Disconnect the throttle body connector.
• Disconnect the C2 PCM harness connector.
• Measure the resistance between the TP signal 1 circuit and the TP signal 2 in the throttle body harness connector.
Is the resistance less than 100 ohms?
Yes
• Repair the short between the TP signal 1 circuit and the TP signal 2 circuit.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
No
• Go to Test Step 7 => [ Test
Step 7 - Throttle Position Sensor 1 Voltage ]
Test Step 7 - Throttle Position Sensor 1 Voltage
• Turn the ignition OFF.
• Connect the PCM connector.
• Turn the ignition ON.
• With a scan tool, read the throttle position sensor 1 voltage.
• Turn the ignition OFF.
• Connect a jumper wire between the TP signal 1 circuit and the TP sensor ground circuit in the throttle body harness connector.
• Turn the ignition ON.
• With a scan tool, read the throttle position sensor 1 voltage.
• The circuit voltage should change from approximately 5.0 volts (plus or minus 0.1 volt) with the throttle body connector disconnected to 0.0 volts (plus or minus 0.1 volt) with the jumper wire in place.
Does the scan tool display the voltage as described?
Yes
• Go to Test Step 8 => [ Test
Step 8 - Throttle Position Sensor 2 Voltage ]
No
• Go to Test Step 10 => [ Test
Step 10 - PCM ]
Test Step 8 - Throttle Position Sensor 2 Voltage
• With a scan tool, read the throttle position sensor 2 voltage.
• Turn the ignition OFF.
• Connect the jumper wire between the TP signal 2 circuit and the 5 Volt supply circuit in the throttle body harness connector.
• Turn the ignition ON.
• With a scan tool, read the throttle position sensor 2 voltage.
• The circuit voltage should change from approximately 0.0 volts (plus or minus 0.1 volt) with the throttle body connector disconnected to 5.0 volts (plus or minus 0.1 volt) with the jumper wire in place.
Does the scan tool display the voltage as described?
Yes
• Go to Test Step 9 => [ Test
Step 9 - Throttle Body ]
No
• Go to Test Step 10 => [ Test
Step 10 - PCM ]
Test Step 9 - Throttle Body
• Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the throttle body and the PCM.
• Look for any chafed, pierced, pinched, or partially broken wires.
• Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related connectors.
• Monitor the scan tool data relative to this circuit and wiggle test the wiring and connectors.
• Look for the data to change or for the DTC to reset during the wiggle test.
• Refer to any technical service bulletins that may apply.
Were any problems found?
Yes
• Repair as necessary.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
No
• Replace the throttle body.Disconnect the battery prior to replacing the throttle body. With the scan tool, perform the ETC relearn function after replacement.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
Test Step 10 - PCM
• Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the throttle body and the PCM.
• Look for any chafed, pierced, pinched, or partially broken wires.
• Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the related connectors.
• Monitor the scan tool data relative to this circuit and wiggle test the wiring and connectors.
• Look for the data to change or for the DTC to reset during the wiggle test.
• Refer to any technical service bulletins that may apply.
Were any problems found?
Yes
• Repair as necessary.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test
No
• Replace and program the PCM.
• Perform the PCM Verification Test. Refer to => Non-DTC
Based Diagnostics. PCM Verification Test