Symptoms
Potential symptoms include:
- MIL (Malfunction Indicator Lamp) illumination
- Misfires at idle or highway speed
- Poor idle quality
- May not idle
- May start and stall
Causes
Potential causes of P2120 code include:
- Sticking throttle return spring
- Corrosion of MAP or TPS connectors
- Misrouted harness causing chafing
- Faulty TPS
- Faulty PCM
Possible Solutions
If you have access to a scan tool, with KOEO (Key On Engine Off), monitor TPS voltage. With the throttle closed, voltage should be approximately 0.45 volts. It should gradually sweep upward to about 4.5 to 5 volts as you press the accelerator. Sometimes only an oscilloscope can capture an intermittent problem in the TPS signal voltage. If you notice an issue in the TPS sweep voltage, replace the TPS.
NOTE: Some TPS sensors require fine adjustment. If you are not comfortable using a DVOM (Digital Volt Ohm Meter) to adjust the new TPS, then it is best to take the vehicle to a shop. If the voltage is not 0.45 volts (+ or – approximately 0.3 volts) with the throttle closed or if the reading is “stuck,” disconnect the TPS connector. With KOEO, check for the 5-volt reference voltage present at the connector and a good ground. You can check the signal circuit continuity by jumpering a fuse wire between the TPS connector ground circuit and the signal circuit. If the TPS reading on the scan tool now reads zero, replace the TPS. However, if it does not change the reading to zero, check for an open or short in the signal wire and if none is found, suspect a faulty PCM. If manipulating the TPS wiring harness causes a change at idle, suspect a faulty TPS.