P2100

Actuator A Control Motor Circuit/Open

P2100 is a generic OBD-II powertrain diagnostic trouble code: Actuator A Control Motor Circuit/Open. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P2100
Group
Powertrain
System
SCR/AdBlue
Severity
Critical (limp mode / no-start)
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What P2100 means

P2100 is set when the PCM (or dedicated TAC module) detects an open circuit condition in the throttle actuator 'A' control motor drive circuit. Drive-by-wire (electronic throttle control) systems replace the mechanical throttle cable with two sensors on the accelerator pedal (APP sensors) that relay the driver's input electronically; the PCM then commands a small DC motor inside the throttle body to move the throttle plate to the precise angle requested. P2100 indicates the PCM is unable to complete the drive circuit to that motor — current cannot flow — which is electrically consistent with an open wire, a failed connector, or an internal motor open-circuit winding.

Because the PCM has no way to control throttle opening with an open motor circuit, virtually all vehicles will immediately enter a fail-safe or limp-home mode when P2100 is logged. Limp mode typically holds the throttle plate at a small fixed opening (typically 5–10 percent, producing only idle or very limited power), disables non-essential systems such as air conditioning, and may cap vehicle speed to protect occupants and other road users. The MIL and, on many platforms, a separate 'Reduced Engine Power' or wrench warning lamp will illuminate.

Open-circuit faults in the motor drive circuit are most commonly caused by physical wiring damage — particularly corrosion at the throttle body connector, which is exposed to heat cycling and moisture. A failed TAC motor winding is the next most common cause. PCM drive-stage failure is possible but uncommon.

Common causes

Most-frequently reported root causes when P2100 is logged.

  • 1
    Open circuit in the throttle actuator motor wiring harness (broken conductor, chafed insulation leading to complete wire break).
  • 2
    Corroded, spread, or damaged terminals at the throttle body electrical connector.
  • 3
    Failed internal TAC motor winding (open coil) inside the throttle body assembly.
  • 4
    Faulty or failed Accelerator Pedal Position (APP) sensor assembly sending no signal, triggering a system-level fault.
  • 5
    PCM internal drive-stage failure preventing current from being supplied to the motor circuit (rare).
  • 6
    Connector pin retainer failure causing intermittent or complete loss of electrical contact under vibration.

Symptoms drivers notice

Immediate entry into limp/fail-safe mode with severely restricted throttle response.
MIL and 'Reduced Engine Power' or wrench warning lamp illuminated simultaneously.
Engine holds at or near idle regardless of accelerator pedal input.
Air conditioning and other non-essential systems automatically disabled by the PCM.
Vehicle may not restart without clearing the fault and repairing the circuit.
No throttle response variation — the throttle plate is mechanically held at a fixed opening.

How to diagnose P2100

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and record P2100 plus any companion codes (e.g. P0120/P0220 APP sensor codes, P2101 TAC motor range/performance); companion codes narrow the fault location significantly.
  2. 2
    Visually inspect the throttle body connector and harness for corrosion, melted insulation, or physical damage; unplug the connector and examine all terminals for spread pins or corrosion.
  3. 3
    With the connector unplugged, measure resistance across the TAC motor terminals (pins vary by vehicle — consult the wiring diagram); an infinite (OL) reading confirms an open motor winding.
  4. 4
    With the ignition on and the connector unplugged, backprobe the PCM-side harness for the expected supply voltage and verify continuity of the motor ground return to chassis ground.
  5. 5
    Inspect the harness along its full run from the PCM to the throttle body for chafing against hot or sharp components.
  6. 6
    If wiring and connector test good, replace the throttle body assembly (motor and sensor integrated unit on most platforms) and perform the throttle body relearn procedure.
  7. 7
    Clear codes, perform a test drive including steady throttle and WOT inputs, and confirm the fault does not return.

Related powertrain codes

Frequently asked questions

Is it safe to drive in limp mode caused by P2100?

Limp mode is an emergency safety measure — the vehicle is intentionally restricted to low power. It is not safe to drive in normal traffic conditions at limp-mode speeds. Drive only the minimum distance needed to reach a safe location or workshop.

Does P2100 always mean the throttle body needs replacing?

No. P2100 is an open-circuit electrical fault. A broken wire or corroded connector can cause exactly the same code at a fraction of the cost. Always diagnose the full circuit before replacing the throttle body assembly.

Why does an open motor circuit force limp mode rather than just setting a code?

The TAC system is a safety-critical, closed-loop actuator. If the PCM cannot confirm that the throttle plate is responding to its commands, uncontrolled acceleration is theoretically possible. Fail-safe mode prevents that by limiting throttle to a known, fixed safe opening.

What is a throttle body relearn procedure and why is it needed after replacement?

After replacing a throttle body, the PCM must learn the closed-throttle reference position (the minimum stop angle for idle). Most platforms require the ignition to be cycled through a specific sequence or a key-on scan-tool relearn command. Skipping this step can cause erratic idle, stalling, or repeated codes.

Disabling P2100 in software

RaceTune can permanently disable P2100 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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