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DTC codes / Ford codes / P1579

P1579 · FordETC In Power Limiting Mode

P1579 on Ford vehicles indicates that the Electronic Throttle Control (ETC) system has entered a power-limiting mode, often called limp mode, because the Powertrain Control Module (PCM) detected a fault that prevents safe full-range throttle operation. The PCM has commanded reduced engine power to protect the driver and the engine until the underlying issue is resolved.

SystemPowertrain
Code typeFord specific
SeverityHigh
Fix difficultyProfessional
AreaVehicle speed, idle control and auxiliary inputs

Symptoms you may notice

  • The engine may idle roughly or at an elevated speed, and the accelerator pedal may feel unresponsive or sluggish.
  • The vehicle may be limited to a low maximum speed, typically around 30–40 mph, making highway driving impossible.
  • The wrench or check engine light may be illuminated, and a message such as 'Engine Power Reduced' may appear on the dashboard.
  • The transmission may shift harshly or refuse to upshift normally due to the reduced power strategy.
  • Often no symptoms besides the warning light if the fault is intermittent and the system has not fully entered limp mode.
  • The cruise control may be disabled, and the electronic throttle may feel like it has a dead zone at the beginning of pedal travel.

Common causes, most likely first

  1. A faulty accelerator pedal position (APP) sensor or its wiring, which sends incorrect pedal position signals to the PCM.
  2. A dirty or failing electronic throttle body (ETB) causing the throttle plate to stick or not reach commanded positions.
  3. Damaged or corroded wiring in the ETC circuit, including the throttle body connector or pedal sensor harness.
  4. A PCM software issue or internal fault that incorrectly triggers power limiting mode.
  5. Low battery voltage or a weak charging system causing the ETC module to malfunction.
  6. A malfunctioning throttle actuator control (TAC) motor inside the throttle body.
  7. Aftermarket electronic accessories improperly installed, causing electrical interference with the ETC signals.

How to diagnose and fix it

  1. Scan all modules for stored codes and freeze-frame data to confirm P1579 and identify any related ETC or APP sensor codes.
  2. Inspect the throttle body and accelerator pedal connectors for corrosion, loose pins, or damaged wiring, and repair as needed.
  3. Clean the throttle body bore and plate with approved cleaner, then perform a throttle body relearn procedure using a scan tool.
  4. Check battery voltage and charging system output; a weak battery can cause spurious ETC codes, so replace it if it fails a load test.
  5. Perform a pinpoint test for the APP sensor and throttle body circuits using a multimeter to check for opens, shorts, or excessive resistance.
  6. Reprogram or update the PCM with the latest calibration from Ford if a software issue is suspected.
  7. Replace the electronic throttle body or accelerator pedal assembly only after electrical and mechanical checks confirm a failed component.

Before you replace the throttle body

  • A dirty throttle body is a common cause of P1579 on Fords, and cleaning it often resolves the code without any parts replacement, but a relearn procedure is mandatory afterward.
  • The code can be set by a weak or failing battery, so always load-test the battery before condemning expensive electronic components.
  • Intermittent P1579 codes often stem from chafed wiring near the throttle body or pedal, especially where the harness rubs against engine components.
  • Aftermarket remote starters or alarm systems tapped into the pedal wiring can introduce voltage spikes that trigger power limiting mode.
  • P1579 does not always mean the throttle body itself is faulty; the PCM may set it due to a mismatch between the two APP sensor signals, so check both signals simultaneously with a scan tool.

Can I keep driving with P1579?

Driving with P1579 is not recommended because the vehicle may enter limp mode without warning, limiting speed and acceleration unpredictably. If you must drive, proceed directly to a repair shop at low speed and avoid highways or situations requiring sudden acceleration.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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