P0121-Throttle Position Sensor 1 performance
July 24, 2017
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P0121 code - With the engine running, P2135 DTC active. Set conditions, when fault P2135 is active, the Powertrain Control Module (PCM) looks at the difference between calculated MAP based on TPS 1 input and sensed MAP. The same is done for TPS. If the PCM determines that the TPS 1 error is larges than the TPS 2 error, this fault is set. Default actions, the MIL light will illuminate, ETC light will illuminate.
Possible causes P0121 code:
Step 2. Throttle follower test
Step 6. Throttle Position Sensor
Possible causes P0121 code:
- High resistance in the TPS 1 signal circuit.
- High resistance in the 5 Volt supply circuit.
- High resistance in the TPS return circuit.
- Throttle Body.
- Powertrain Control Module.
Diagnose code P0121-Throttle Position Sensor 1 performance
Step 1. Check active DTC
Diagnose and repair any Throttle Body circuit, system voltage or 5 volt reference DTC before continuing with this test. Start the engine and allow it to idle.
Warning : When the enngine 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 may result in possible serious or fatal injury.
With the scan tool, read DTC. If the DTC does not reset it may be necessary to test drive the vehicle.
Is the DTC active or pending?
Yes, go to step 2.
No, perform the PCM intermittent condition.
Step 2. Throttle follower test
Turn the ignition on, with the scan tool, perform the ETC Throttle follower Test and monitor the TPS 1 or TPS 2 voltage. Slowly press the accelerator pedal down. The voltage for TPS 1 should start at approximately 0.7 volts and increase to approximately 4.3 volts.
Is the TPS 1 voltage within the range of the listed specification?
Yes, perform the PCM intermittent condition.
No, go to step 3.
Step 3. Check the TPS 2 signal circuit for excessive resistance
Step 3. Check the TPS 2 signal circuit for excessive resistance
Turn the ignition off, disconnect the Throttle Body harness connector. Disconnect the PCM harness connector, measure the resistance of the TPS 2 signal circuit between the Throttle Body harness connector and the PCM harness connector.
Is the resistance below 3.0 Ohms?
Yes, go to step 4.
No, repair the excessive resistance in the TPS 2 signal circuit.
Step 4. Check the 5 Volt supply circuit for excessive resistance
Step 4. Check the 5 Volt supply circuit for excessive resistance
Measure the resistance of the 5 Volt supply circuit between the Throttle Body harness connector and PCM harness connector.
Is the resistance below 3.0 Ohms?
Yes, go to step 5.
No, repair the excessive resistance in the 5 volt supply circuit.
Step 5. Check the TPS return circuit for excessive resistance
Step 5. Check the TPS return circuit for excessive resistance
Measure the resistance of the TPS return circuit between the Throttle Body harness connector and PCM harness connector.
Is the resistance below 3.0 Ohms?
Yes, go to step 6.
No, repair the excessive resistance in the TPS return circuit.
Step 6. Throttle Position Sensor
Reconnect the PCM harness connector. Turn the ignition on, with the scan tool, monitor the TPS 2 voltage. Connect a jumper between the TPS 2 signal circuit and the TPS return circuit. The TPS 2 voltage should change from approximately 5.0 volts with the connector unplugged to 0.0 volts with the jumper in place.
Is the voltage reading within the listed specification when the jumper is installed?
Yes, verify that there is good pin to terminal contact in the Throttle Body and Powertrain Control Module (PCM) connectors. If no problems are found replace the Throttle Body Assembly.
No, go to step 7.
Note : Remove the jumper before continuing.
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