P2120 Throttle Position Sensor / Switch C Circuit Malfunction

P2120 Throttle Position Sensor / Switch C Circuit Malfunction

OBD-II DTC Datasheet

Malfunction of a chain of the sensor of position of a butterfly valve / pedal / switch "D"

What does this mean?

This Diagnostic Trouble Code (DTC) is a generic transmission code, which means it applies to OBD-II equipped vehicles. Although general, specific repair steps may differ depending on the brand / model.

TPS (Throttle Position Sensor) is a potentiometer mounted on the throttle body. It determines the throttle angle. When the throttle is moving, the TPS sends a signal to the PCM (Powertrain Control Module). Typically a 5-wire sensor: XNUMXV reference from PCM to TPS, ground from PCM to TPS, and signal return from TPS to PCM.

The TPS sends throttle position information back to the PCM over this signal wire. When the throttle is closed, the signal is about 45 volts. With WOT (Wide Open Throttle), the TPS signal voltage approaches the full 5 volts. When the PCM detects a voltage outside the normal operating range, P2120 is set. The letter "D" refers to a specific circuit, sensor, or area of ​​a specific circuit.

NOTE: The PCM knows that any large change in throttle position means a corresponding change in manifold pressure (MAP). On some models, PCM will monitor MAP and TPS for comparison. This means that if the PCM sees a large percentage change in throttle position, it expects to see a corresponding change in manifold pressure and vice versa. If he does not see this comparative change, P2120 may be set. This does not apply to all models.

symptoms

Possible symptoms include:

• MIL Illumination (Malfunction Indicator)
• Idle or highway misfire
• Poor idle quality
• May not be idle
• Probably starts and stalls

reasons

Possible causes of a P2120 code include:

• Stuck throttle return spring
• Corrosion on MAP or TPS connector
• An incorrectly routed belt causes chafing
• Bad TPS
• Bad PCM

Possible solutions

If you have access to a scan tool, observe the TPS voltage with KOEO (Engine Off Key). With the throttle closed, the voltage should be about 45 V. It should gradually rise to about 4.5-5 volts as you push the throttle. Sometimes, only the oscilloscope can capture the periodic voltage surges of the TPS signal. If you notice a failure in the TPS sweep voltage, replace the TPS.

NOTE. Some TPS sensors require fine tuning. If you don't feel comfortable using the DVOM (Digital Volt Ohmmeter) to set up your new TPS, your best bet is to take your car to a shop. If the voltage is not 45V (+ or -3V or so) with the throttle closed, or if the reading is stuck, disconnect the TPS connector. Using KOEO, check for a 5V reference on the connector and a good ground. You can test the signal circuit by moving a fusible wire between the ground circuit of the TPS connector and the signal circuit. If the TPS reading on the scan tool now reads zero, replace the TPS. However, if this does not change the reading to zero, check for an open or short in the signal wire, and if nothing is found, suspect a bad PCM. If manipulation of the TPS harness causes any change in idle, then suspect the TPS is bad.

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