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DTC codes / Ford codes / P1644

P1644 · FordFuel Pump Speed Control Circuit Malfunction

P1644 on Ford vehicles indicates that the powertrain control module (PCM) has detected an abnormal condition in the fuel pump speed control circuit, which typically uses a duty-cycle signal to vary pump speed. The PCM monitors the circuit for expected voltage or current feedback and sets this code when the signal is out of range, stuck, or missing.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light, often with no other noticeable symptoms
  • Engine may crank but fail to start or stall shortly after starting
  • Rough idle or hesitation during acceleration due to inconsistent fuel delivery
  • Whining or buzzing noise from the fuel tank area if the pump runs at full speed continuously
  • Reduced engine power or limp mode in some Ford models
  • Intermittent stalling while driving, especially at low speeds

Common causes, most likely first

  1. Failed fuel pump control module (FPDM) or fuel pump driver module, common on Ford vehicles
  2. Damaged or corroded wiring harness or connector at the fuel pump or FPDM
  3. Faulty fuel pump assembly with an internal speed control fault
  4. Blown fuse or relay in the fuel pump control circuit
  5. PCM software issue or internal driver failure (less common)
  6. Poor ground connection for the fuel pump or control module

How to diagnose and fix it

  1. Inspect the fuel pump control module and its connectors for corrosion, water intrusion, or physical damage
  2. Check all fuses and relays related to the fuel pump circuit and replace as needed
  3. Perform a voltage drop test on the fuel pump power and ground circuits to identify high resistance
  4. Use a scan tool to command the fuel pump on and off while monitoring the control circuit duty cycle
  5. Test the fuel pump control module with a known-good unit if available, or follow Ford diagnostic procedures
  6. Check for technical service bulletins (TSBs) or PCM reprogramming updates for the specific Ford model
  7. Replace the fuel pump control module or fuel pump assembly only after confirming the fault

Common Misdiagnosis Traps for P1644

  • A failed fuel pump control module often mimics a bad fuel pump, leading to unnecessary pump replacement; always test the module first.
  • Corroded connectors at the fuel pump control module, especially in models where it is mounted under the vehicle, are a frequent cause that is easily overlooked.
  • The code can set intermittently due to a loose ground connection, so a wiggle test of the harness while monitoring live data is essential.
  • Some Ford vehicles require PCM reprogramming after replacing the fuel pump control module, and skipping this step can cause the code to return.
  • A weak battery or charging system issue can cause voltage spikes that trigger this code, so check the charging system before condemning components.

Can I keep driving with P1644?

If the vehicle is running normally, you can drive it to a repair shop, but avoid heavy acceleration or towing. If the engine stalls or lacks power, stop driving and have the vehicle towed to prevent safety risks.

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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