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P2121 is a diagnostic trouble code (DTC) for "Throttle/Pedal Position Sensor/Switch D Circuit Range/Performance". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.
The powertrain control module (PCM) or another related control module has detected a problem in a particular throttle position sensor circuit. Related modules can include:
If the throttle actuator control motor circuit sends a reading to the PCM that is out of normal specs, a trouble code will be stored and the malfunction indicator lamp (MIL) will illuminate. Some models may require several drive cycles with the failure to illuminate the MIL, while others will activate it immediately.
An OBD-II scanner/code reader, digital volt/ohmmeter (DVOM), oscilloscope and manufacturer’s service manual will be necessary for this diagnosis and repair. NOTE: P2121 codes only apply to vehicles with an electronically controlled “drive by wire” throttle body. These are designed with a sensor on the accelerator pedal arm which sends a voltage signal to the PCM or other related controller. This is what commands the throttle body to open or close, depending on conditions. The PCM enables the throttle actuator motor in the required direction by changing voltage and polarity. As the throttle actuator turns, it turns a gear which meshes with a larger gear, allowing the throttle plate to open quickly and suddenly or slowly, depending on the driver input.
Often, technicians treat symptoms rather than the cause of a problem when multiple codes are registered. Codes related to lean exhaust, engine misfires, fuel injectors or numerous other codes can be easy to misdiagnosis when accompanied by a controller communication code. Remember to diagnose the codes in the order in which they were stored, to help your chances for a proper diagnosis and repair. Using the scanner’s freeze frame function can help determine the order in which codes were stored.
A P2121 code can result in symptoms that make the vehicle undrivable.
On post-2008 vehicles, a code such as P2121 may be traced to the CAN bus. The CAN bus is a conglomeration of sensors, wiring harnesses and connectors that enables information to be shared between modules, and it controls almost every electrical function of the vehicle. A technician with a specialized scanner such as Autohex or Tech II can determine CAN-related issues, but it may be something that’s very difficult to diagnose and repair for a non-professional mechanic. Probing each individual circuit, out of hundreds, could result in hours and hours of labor.
Proper service of CAN networks requires a hard drive to retain memory in case of a complete system meltdown; all it can take is one misplaced DVOM probe to cause a catastrophe. A professional technician with a specialized CAN scanner, on the other hand, can determine pin values and control module operation without the risk of a system meltdown. Keep an eye open for engine or transmission ground cables, straps or wires; sometimes these are left dangling after recent repairs.
In many cases, problems like a P2121 are simply beyond the expertise of a non-professional mechanic and should be left to a qualified technician. Sophisticated CAN systems are designed for service by factory-trained technicians and not non-professionals.
YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.