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DTC codes / Ford codes / P1667

P1667 · FordCI Circuit Malfunction

P1667 on Ford vehicles indicates a malfunction in the Continuous Injection (CI) circuit, which is part of the diesel engine management system. The powertrain control module (PCM) has detected an abnormal voltage or current condition in the CI circuit, preventing proper control of the injection system.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light (malfunction indicator lamp).
  • Reduced engine performance or power, especially under load.
  • Rough idle or engine misfire.
  • Poor fuel economy.
  • Difficulty starting or stalling.
  • Often no symptoms besides the warning light.

Common causes, most likely first

  1. Faulty CI circuit wiring or connectors (open, short, or corrosion).
  2. Defective CI control solenoid or actuator.
  3. Failed CI circuit relay or fuse.
  4. PCM software issue or internal fault.
  5. Poor ground connection for the CI circuit.
  6. Damaged or chafed harness near the engine.

How to diagnose and fix it

  1. Check for any related technical service bulletins (TSBs) or recalls for the vehicle.
  2. Inspect the CI circuit wiring and connectors for damage, corrosion, or loose pins.
  3. Test the CI circuit fuse and relay, replacing if faulty.
  4. Measure resistance and voltage at the CI control solenoid to verify operation.
  5. Perform a wiggle test on the harness while monitoring live data to detect intermittent faults.
  6. Reprogram or update the PCM if a known software issue exists.
  7. Replace the faulty CI solenoid or repair wiring as needed, then clear codes and verify.

CI Circuit Faults Often Misdiagnosed

  • A loose or corroded ground connection for the CI circuit can mimic a failed solenoid, so always check grounds before replacing parts.
  • Intermittent wiring faults may not set the code consistently; a wiggle test of the harness while watching live data can reveal the issue.
  • The CI circuit is often confused with the injector circuits, but it controls injection timing and pressure, so symptoms may overlap with other codes.
  • After repairs, the PCM may require a relearn procedure or several drive cycles before the code clears permanently.
  • Some aftermarket accessories or poor electrical repairs can introduce noise into the CI circuit, causing false codes.

Can I keep driving with P1667?

If the vehicle is running normally, you can drive it to a repair shop, but avoid heavy loads or aggressive driving. If performance is noticeably reduced or the engine stalls, stop driving and have it towed to prevent further damage.

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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