Technical Description of OBD-II Trouble Code
Issue with the Range/Performance of Throttle Position Sensor/Switch A Circuit
What does that signify?
This diagnostic trouble code (DTC) is a generic powertrain code that is applicable to vehicles equipped with OBD-II. Although it is a generic code, the specific repair steps may vary depending on the make and model of the vehicle.
The throttle position sensor is a potentiometer that measures the degree of throttle opening. As the throttle is opened, the voltage reading increases.
The powertrain control module (PCM) supplies a 5 Volt reference signal to the throttle position sensor (TPS) and usually a ground as well. The general voltage measurements are: 0.5 Volts at idle and 4.5 Volts at full throttle. If the PCM detects that the throttle angle is greater or less than the expected value for a specific RPM, it will trigger this code.
Potential Symptoms
Symptoms that may be experienced with a P0121 trouble code include:
Causes
A code P0121 may indicate that one or more of the following issues have occurred:
Possible Solutions
1. If you have access to a scan tool, check the idle and wide open throttle (WOT) readings for the TPS. Verify if they are close to the specified values mentioned above. If not, replace the TPS and re-check.
2. To check for an intermittent open or short in the TPS signal, an oscilliscope is required as scan tools may miss intermittent dropouts. Connect an oscilliscope and monitor the signal. It should smoothly sweep up and down without any dropouts or spikes.
3. If no issues are observed, perform a wiggle test by moving the connector and harness while observing the signal pattern. Does it drop out? If so, replace the TPS and re-check.
4. If there is no TPS signal, check for a 5 Volt reference at the connector. If present, inspect the ground circuit for any open or short circuits.
5. Ensure that the signal circuit does not have a voltage of 12V. It should never have battery voltage. If it does, trace the circuit for a short to voltage and repair it.
6. Examine the connector for any water and replace the TPS if necessary.
Other DTCs related to TPS sensor and circuit: P0120, P0122, P0123, P0124
