Throttle Actuator Control Motor Circuit/Open
The P2100 code indicates that the Powertrain Control Module (PCM) has detected an open circuit in the throttle actuator control (TAC) motor circuit. This means the engine computer cannot communicate with or control the electric motor responsible for opening and closing the throttle plate.
This code is highly urgent because a lack of throttle control will force the vehicle into a fail-safe or limp mode with severely reduced power. It can leave you stranded or unable to accelerate safely in traffic.
Common symptoms
- Illuminated Check Engine Light
- Vehicle enters fail-safe or limp mode with limited speed
- No response or very poor response when pressing the accelerator pedal
- Engine idles roughly, surges, or stalls
- Engine may crank but fail to start
Likely causes
- Disconnected, damaged, or corroded wiring harness at the throttle body
- Faulty throttle actuator control (TAC) motor with an internal open circuit
- Blown fuse or faulty relay providing power to the TAC system
- Poor electrical connection at the Powertrain Control Module (PCM)
- Failed Powertrain Control Module (PCM)
What to check before replacing parts
Inspect the throttle body wiring harness and connector.
Look for: Look for disconnected plugs, broken wires, pushed-out pins, or heavy corrosion that would cause an open circuit.
Check the fuses and relays related to the electronic throttle control system.
Look for: Look for a blown fuse or a faulty relay that is failing to supply voltage to the TAC motor circuit.
Test the TAC motor circuit for continuity using a digital multimeter.
Look for: Look for infinite resistance (OL) on the multimeter, which confirms a break in the wiring between the PCM and the throttle body.
Measure the internal resistance of the throttle actuator motor itself.
Look for: Look for a resistance reading that falls outside the manufacturer's specified range, indicating an internal open in the motor.
Check for voltage and ground signals from the PCM at the throttle body connector while the key is on.
Look for: Look for missing voltage or ground, which points to a wiring issue further up the harness or a faulty PCM.
This page explains the generic P2100 definition and is general reference information, not a diagnosis for your specific vehicle. Actual causes, severity, and repairs vary by make, model, engine, and mileage — always confirm with a scan tool and a qualified technician before replacing parts.
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