P2105 – Throttle actuator control (TAC) system – forced engine shut down mode

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By Reinier (Contact Me)
Last Updated 2020-08-11
Automobile Repair Shop Owner
CodeFault LocationProbable Cause
P2105 Throttle actuator control (TAC) system - forced engine shut down mode
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Wiring, TAC motor, APP sensor, ECM

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Table of Contents

  1. What Does Code P2105 Mean?
  2. Where is the P2105 sensor located?
  3. What are the common causes of code P2105?
  4. What are the symptoms of code P2105?
  5. Get Help with P2105

What Does Code P2105 Mean?

OBD II fault code P2105 is a generic trouble code that is defined as “Throttle Actuator Control System – Forced Engine Shutdown”, and is set when the PCM (Powertrain Control Module) detects a fault, failure, defect, or malfunction in any system, component, or circuit that controls, or monitors the operation of the electronic throttle control system.

NOTE:  Note that this code only applies to vehicles that use drive-by-wire throttle control systems and that in all cases where this code is set on affected vehicles, the PCM will also initiate a fail-safe or limp mode to limit engine power severely as a safety measure. In all cases, the fail-safe or limp mode will persist until the fault is corrected.

Unlike conventional throttle control systems in which there is a physical connection in the form of a control cable between the throttle pedal and the throttle plate, drive-by-wire systems use data from several sensors to control, manage, and monitor the position of the throttle plate. The principal sensors in these systems are typically the throttle pedal position sensor and a throttle plate position sensor that generate signal voltages that are used to activate stepper motor in the throttle body.

The throttle plate is connected to the stepper motor by a set of drive gears that transfer the motors’ rotation to the actual throttle plate as a means to control throttle inputs. An integrated throttle plate position sensor monitors the position of the throttle plate, and this information is used to correlate the position of the throttle pedal with the actual position of the throttle plate. In practice though, the throttle plate’s position is converted into degrees (or sometimes, into a percentage) of opening, which is then used by the PCM to compare the throttle plate’s actual position relative to the desired or commanded position given the current operating conditions.

For obvious reasons, all parts, components, and circuits involved in electronic throttle control systems need to be in perfect working order for the system to operate safely and reliably. While most systems work reliably for long periods, issues like component wear, damaged wiring, software issues, and other factors can cause the system to become unsafe, to work erratically, or to not work at all. Therefore, when the PCM detects any condition in any implicated component of the throttle control system, as well as in associated systems that affect, or can potentially affect, the safe and reliable operation of the electronic throttle control system it will set code P2105, illuminate a warning light, and either initiate a fail-safe or limp mode or shut down the engine.

Where is the P2105 sensor located?

This image shows the typical construction of an electronically controlled throttle body, with the position of the stepper motor relative to the drive gears visible. In terms of physical location, these types of throttle bodies are located in the same position in the intake duct as conventional throttle bodies.

In terms of appearance, the only difference between conventional throttle bodies and electronically controlled throttle bodies is that conventional units can be identified by the presence of a control cable, which electronically controlled units do not have.

What are the common causes of code P2105?

While the typical causes of code P2105 vary somewhat between applications and designs, it should be noted that some causes of this code on some applications are neither directly related to throttle control component/system failure, nor to reasonable wear and tear of moving components in the throttle control system. Therefore, this list of possible causes of code P2105 on all applications is neither exhaustive nor complete, but known causes that are not directly attributable to throttle control system or component failure will be indicated by an asterisk (*).

  • Engine overheating*
  • Engine coolant leaks*
  • Drive axle modifications, including mismatched wheel diameters*
  • EGR (Exhaust Gas Recirculation) valve failure*
  • Faulty or defective Mass Airflow Sensor*
  • ABS brake system defects*
  • Defects, failures, and/or malfunctions in cruise control and stability control systems, particularly in adaptive cruise control systems*
  • Some types of automatic transmission system defects*
  • Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors almost anywhere in the throttle control system, or associated systems
  • Abnormally high or low system voltages
  • Faulty or defective stepper motor, and/or excessive mechanical wear of drive gears
  • Faulty or defective pedal position sensor
  • Faulty or defective throttle plate position sensor
  • Corrupted PCM software

What are the symptoms of code P2105?

Typical symptoms of code P2105 are the same across all applications, and could include the following-

  • Stored trouble code and illuminated MIL (CHECK ENGINE) light
  • In most cases, multiple additional trouble codes that might not seem to be related to P2105 may be present along with P2105
  • Vehicle will almost certainly be in a fail-safe or limp mode that will persist until the fault is found and corrected but note that in some cases, the PCM may shut down the engine and will not allow it to be restarted until the fault is corrected

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