P0121-THROTTLE POSITION SENSOR 1 PERFORMANCE





For a complete wiring diagram Refer to Section 8W.



Possible Causes
EXCESSIVE RESISTANCE IN THE (K22) TP SIGNAL 1 CIRCUIT
EXCESSIVE RESISTANCE IN THE (K122) TP SIGNAL 2 CIRCUIT
EXCESSIVE RESISTANCE IN THE (F855) 5-VOLT SUPPLY CIRCUIT
EXCESSIVE RESISTANCE IN THE (K922) TP RETURN CIRCUIT
(K22) TP SIGNAL 1 CIRCUIT SHORTED TO THE (K122) TP SIGNAL 2 CIRCUIT
THROTTLE POSITION SENSOR/THROTTLE BODY
PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 9 - ENGINE - DIAGNOSIS AND TESTING).



Diagnostic Test

1. ACTIVE DTC

NOTE: When this DTC is Active the engine speed, torque, and vehicle speed are limited to a Limp in mode.

NOTE: Diagnose any other TP Sensor DTC(s) before continuing.

NOTE: The throttle plate should be free from binding and carbon build up.

NOTE: Make sure the throttle plate is at the idle position.

NOTE: Inspect the engine for vacuum leaks.


Ignition on, engine not running.
With a scan tool, select View DTCs.

Is the DTC active at this time?

Yes


No

2. EXCESSIVE RESISTANCE IN THE (K22) TP SIGNAL 1 CIRCUIT

Turn the ignition off.
Disconnect the C2 PCM harness connector.

CAUTION: 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 along with the #8815-1 to perform the diagnosis.


Using a voltmeter perform a voltage drop test. Backprobe the (K22) TP Signal 1 circuit at the Throttle Body harness connector and to probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

WARNING: 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 and allow it to reach normal operating temperature.
Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes


No

3. EXCESSIVE RESISTANCE IN THE (K122) TP SIGNAL 2 CIRCUIT

Turn the ignition off.
Move the voltmeter leads to backprobe the (K122) TP Signal 2 circuit at the Throttle Body harness connector and to probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

WARNING: 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 and allow it to reach normal operating temperature.
Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes


No

4. EXCESSIVE RESISTANCE IN THE (F855) 5-VOLT SUPPLY CIRCUIT

Turn the ignition off.
Move the voltmeter leads to backprobe the (F855) 5-volt Supply circuit at the Throttle Body harness connector and to probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

WARNING: 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 and allow it to reach normal operating temperature.
Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes


No

5. EXCESSIVE RESISTANCE IN THE (K922) TP RETURN CIRCUIT

Turn the ignition off.
Move the voltmeter leads to backprobe the (K922) TP Return circuit at the Throttle Body harness connector and to probe the appropriate terminal of the special tool #8815. Make sure the voltmeter leads are connected so a positive polarity is displayed on the voltmeter.

WARNING: 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 and allow it to reach normal operating temperature.
Monitor the voltmeter.

Is the voltage below 0.5 of a volt?

Yes


No

6. (K22) TP SIGNAL 1 CIRCUIT SHORTED TO THE (K122) TP SIGNAL 2 CIRCUIT



Measure the resistance between the (K22) TP Signal 1 circuit and the (K122) TP Signal 2 circuit in the Throttle Body harness connector.

Is the resistance below 5.0 ohms?

Yes


No

7. THROTTLE POSITION SENSOR





Turn the ignition off.
Connect the C2 PCM harness connector.
Ignition on, engine not running.
With a scan tool, monitor the TP Sensor No.1 and No.2 voltage.
Connect a jumper wire between the (K922) TP Return circuit and the (K22) TP Signal 1 circuit.

NOTE: TP Sensor No.1 voltage should change from approximately 4.5 volts to less than 0.5 of a volt.


For TP Sensor No.2, connect a jumper wire between (F855) 5-volt Supply circuit and the (K122) TP Signal 2 circuit.

NOTE: TP Sensor No.2 voltage should change from approximately 0 volts to 5.0 volts?



Is the voltage reading within the listed specification when the jumper wire is installed?

Yes


No

8. PCM

NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.


Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.

Were there any problems found?

Yes


No

9. THROTTLE FOLLOWER TEST

Ignition on, engine not running.
With a scan tool, perform the Throttle Follower Test and monitor the TP Sensor No.1 or No.2 voltage.
Slowly press the throttle pedal down.
The voltage for TP Sensor No.1 should start at approximately 0.3 of a volt and increase to above 4.7 volts.
The voltage for TP Sensor No.2 should start at approximately 4.7 volts and decrease to approximately 0.3 of a volt.

Is the voltage within the range of the listed specification for the appropriate Sensor?

Yes


No