P2123 Throttle/Pedal Position Sensor/Switch “D” Circuit High
OBD-II Trouble Code Technical Description
Throttle/Pedal Position Sensor/Switch "D" Circuit High Input
What does that mean?
This diagnostic trouble code (DTC) is a generic powertrain code, which means that it applies to OBD-II equipped vehicles. Although generic, the specific repair steps may vary depending on make/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 reliable vehicle information source (All Data DIY will work) for particulars for the vehicle in question. This code is only used in vehicles that are equipped with drive by wire (DBW) systems.
The PCM controls the DBW system using a throttle actuator motor, one or more pedal position sensors (sometimes referred to as accelerator pedal position sensors), and multiple throttle position sensors. The sensors are provided with a reference voltage (typically 5-volts) and a ground. Most TPS/PPS sensors are of the potentiometer type and they complete the respective circuit. A pivoting fulcrum extension, on the accelerator pedal or the throttle plate shaft, actuates the contacts of the sensor. Sensor resistance changes, as the contacts are moved across the sensor circuit board, causing variations in circuit resistance and signal input voltage to the PCM.
If signal input voltage is greater than a programmed limit, for an extended period of time and under a certain set of circumstances, a code P2123 will be stored and a malfunction indicator lamp (MIL) may be illuminated.
Symptoms / Severity
When this code is stored, the PCM will usually enter limp in mode. Engine acceleration will be severely limited (if not disabled) in this mode. Symptoms of a P2123 code may include:
Causes
Possible causes for this engine code include:
Diagnostic and Repair Procedures
A good starting point is always to check for technical service bulletins (TSB) for your particular vehicle. Your issue may be a known issue with a known fix put out by the manufacturer and can save you time and money during diagnosis.
I would gain access to a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a vehicle information source like All Data (DIY) to diagnose a code P2123.
I would make the first step of my diagnosis a visual inspection of all system related wiring and connectors. I also like to check the throttle plate for signs of carbon buildup or damage. Excessive carbon buildup, that holds the throttle body open at startup, may cause a code P2123 to be stored. Clean carbon from the throttle body according to manufacturer’s recommendations and repair or replace defective wiring or components as required, then retest the DBW system.
Next, I connect the scanner to the vehicle diagnostic port and retrieve all stored trouble codes. I write them down just in case I need the order in which the codes were stored. I also like to keep any related freeze frame data. These notes may prove helpful if the P2123 is proven intermittent. Now I clear the codes and test-drive the vehicle. If the code is reset, I continue with my diagnosis
Voltage spikes and inconsistencies, between the TPS, PPS, and the PCM, may be detected using the scanner data stream. Narrow the data stream to display only pertinent data for a faster response. If no spikes and/or inconsistencies are detected, use the DVOM to retrieve live data at each of the sensors, individually. To retrieve live data with the DVOM, connect the test leads to the appropriate signal and ground circuits and observe the DVOM display while operating the DBW. Look for spikes in voltage as the throttle is actuated slowly from the closed position to wide open throttle. Voltage usually ranges from .5-volts at closed throttle to 4.5-volts at wide open throttle. If spikes or other irregularities are detected, suspect that the sensor being tested is defective. An oscilloscope is also a great tool for testing sensor operation.
Additional diagnostic notes:
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"Delete Error Code Permanently, Disable DTC Error Code Function for p2123 in the ECU"
In extreme cases, we even have the option to permanently remove the specific DTC p2123 and disable the function of the specific error code in the ECU. All other fault code functions will then continue to work to protect the engine. This is different from clearing an error code with a diagnostic device. We have the option to permanently remove the function of the specific error code, so that it never comes back. Also emergency running that occurs on the specific error code can be solved in most cases.
Of course we prefer to first try to solve the cause of the error code, but sometimes the only solution is to permanently disable the DTC function of p2123.
