P2123 Throttle Position Sensor / Switch D Circuit High Input

P2123 Throttle Position Sensor / Switch D Circuit High Input

OBD-II DTC Datasheet

Throttle/Pedal Position Sensor/Switch «D» Circuit High Input

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.

When I have encountered a stored code P2123, I have found that it means the powertrain control module (PCM) has detected a high voltage input from the throttle position sensor (TPS) circuit or a particular pedal position sensor (PPS) circuit. The «D» refers to a particular circuit, sensor, or area of a particular circuit.

Consult a trusted source of vehicle information (all DIY data will work) for details of the vehicle in question. This code is only used in vehicles equipped with drive-by-wire (DBW) systems.

The PCM controls the DBW system using the throttle actuator motor, one or more pedal position sensors (sometimes called accelerator pedal position sensors), and multiple throttle position sensors. The sensors have a reference voltage (typically 5 V) and ground. Most TPS / PPS sensors are of the potentiometer type and complete the appropriate circuit. A pivoting axle extension on the accelerator pedal or on the throttle shaft actuates the sensor contacts. Sensor resistance changes as the pins move across the sensor PCB, causing changes in circuit resistance and signal input voltage to the PCM.

If the input signal voltage exceeds the programmed limit, for an extended period of time and under certain circumstances, code P2123 will be stored and a Malfunction Indicator Lamp (MIL) may illuminate.

Symptoms / severity

When this code is stored, the PCM usually enters lame mode. In this mode, engine acceleration will be severely limited (unless disabled). Symptoms of a P2123 code may include:

• Stuck throttle (at all rpm)
• Limited acceleration or no acceleration
• Engine stalls when idling
• Oscillation on acceleration
• Cruise control is not working

reasons

Possible causes of this engine code include:

• Open or short circuit in a chain between TPS, PPS and PCM
• Defective TPS or PPS
• Corroded electrical connectors
• Defective remote control drive motor

Diagnostic and repair procedures

A good starting point is always to check the Technical Service Bulletins (TSB) for your particular vehicle. Your problem may be a known issue with a known manufacturer-released fix and could save you time and money while troubleshooting.

I would have access to a diagnostic scanner, digital volt / ohmmeter (DVOM) and vehicle information source like All Data (DIY) to diagnose the P2123 code.

I would take the first step of my diagnosis by visually inspecting all wiring and connectors associated with the system. I also like to check the throttle body for signs of carbon build-up or damage. Excessive carbon build-up that keeps the throttle body open at startup may result in a P2123 code being stored. Clean any carbon deposits from the throttle body according to the manufacturer's recommendations and repair or replace faulty wiring or components as necessary, then retest the DBW system.

Then I connect the scanner to the car diagnostic port and retrieve all stored DTCs. I write it down just in case I need the order in which the codes were stored. I also like to save any associated freeze frame data. These notes can be helpful if P2123 turns out to be intermittent. Now I am clearing the codes and test drive the car. If the code is cleared, I continue to diagnose

Power surges and mismatches between TPS, PPS and PCM can be detected using the scanner data stream. Narrow your data stream to display only relevant data for a faster response. If no spikes and / or inconsistencies are found, use the DVOM to obtain real-time data from each sensor individually. To obtain real-time data using the DVOM, connect the test leads to the appropriate signal and ground circuits and observe the DVOM display while the DBW is running. Note voltage surges when slowly moving the throttle valve from closed to fully open. The voltage typically ranges from 5V closed throttle to 4.5V wide open throttle. If surges or other abnormalities are found, suspect that the sensor being tested is defective. An oscilloscope is also a great tool for verifying sensor performance.

Additional diagnostic notes:

• Some manufacturers require the throttle body, throttle actuator motor, and all throttle position sensors to be replaced together.

Related DTC discussions

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