Symptoms / Severity
When this code is stored, the PCM typically enters limp mode. Engine acceleration will be severely limited (if not disabled) in this mode. Symptoms of a P2123 code may include:
- Stuck accelerator (at any RPM)
- Limited or no acceleration
- Engine stalling at idle
- Hesitation during acceleration
- Inoperative cruise control
Causes
Possible causes of this engine code include:
- Open or shorted circuits between the TPS, PPS, and PCM
- Faulty TPS or PPS
- Corroded electrical connectors
- Faulty cable actuator motor
Diagnostic and Repair Procedures
A good starting point is always to check the technical service bulletins (TSB) for your specific vehicle. Your issue might be a known problem with a published manufacturer fix, which can save you time and money during diagnosis.
I would use a diagnostic scanner, a digital volt/ohmmeter (DVOM), and a vehicle information source like All Data (DIY) to diagnose a P2123 code.
I would begin my diagnosis with a visual inspection of all cables and connectors related to the system. I also like to check the throttle plate for signs of carbon buildup or damage. Excessive carbon buildup, which keeps the throttle body open at startup, can cause a P2123 code to be stored. Clean the carbon from the throttle body according to manufacturer recommendations and repair or replace any faulty wiring or components as needed, then retest the DBW system.
Next, I connect the scanner to the vehicle’s diagnostic port and retrieve all stored trouble codes. I note them down in case I need the order in which the codes were stored. I also like to save all related freeze frame data. These notes can prove useful if the P2123 turns out to be intermittent. Now, I clear the codes and test the vehicle. If the code resets, I continue my diagnosis.
Voltage spikes and inconsistencies between the TPS, PPS, and PCM can be detected using the scanner’s data stream. Narrow the data stream to display only relevant data for a faster response. If no spikes and/or inconsistencies are detected, use the DVOM to retrieve live data from each sensor 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 voltage spikes when the accelerator is slowly moved from the closed position to wide-open throttle. Voltage typically ranges from 0.5 volts at closed throttle to 4.5 volts at wide-open throttle. If spikes or other irregularities are detected, suspect that the tested sensor is faulty. An oscilloscope is also an excellent tool for testing sensor operation.
Additional Diagnostic Notes:
Some manufacturers require that the throttle body, throttle actuator motor, and all throttle position sensors be replaced together.