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DTC codes / P26xx · Computer and output circuits / P2666

P2666Fuel Shutoff Valve 'B' Control Circuit Low

P2666 indicates that the powertrain control module (PCM) has detected a low-voltage condition on the control circuit for fuel shutoff valve 'B', which is used to stop fuel flow in certain conditions such as during a crash or when the ignition is turned off. The PCM monitors the circuit and sets this code when the voltage on the control side is below the expected threshold, indicating a short to ground or an open circuit.

SystemPowertrain
Code typeGeneric (all makes)
SeverityMedium
Fix difficultyIntermediate
AreaComputer and output circuits

Symptoms you may notice

  • Illumination of the check engine light (malfunction indicator lamp) on the dashboard.
  • Often no symptoms besides the warning light, especially if the valve is not actively used during normal driving.
  • Rough idle or stalling if the valve fails to open when required.
  • Difficulty starting or a no-start condition if the valve remains closed.
  • A noticeable fuel odor or fuel leak in some cases if the valve is stuck open.
  • Reduced engine performance or poor fuel economy if the valve operation is compromised.

Common causes, most likely first

  1. Damaged or corroded wiring harness to the fuel shutoff valve 'B' control circuit, such as a short to ground or an open circuit.
  2. Failed fuel shutoff valve 'B' solenoid or actuator, causing abnormal resistance or a short internally.
  3. Loose or corroded electrical connector at the fuel shutoff valve or PCM.
  4. Faulty powertrain control module (PCM) driver circuit for the valve, though this is less common.
  5. Blown fuse or damaged relay that supplies power to the fuel shutoff valve circuit.
  6. Aftermarket accessories or improper wiring repairs that interfere with the circuit.
  7. Environmental factors such as water intrusion or debris causing corrosion in the circuit.

How to diagnose and fix it

  1. Verify the code with a scan tool and check for any related codes in other systems.
  2. Inspect the wiring harness and connectors at the fuel shutoff valve for visible damage, corrosion, or loose pins.
  3. Test the fuel shutoff valve 'B' solenoid resistance with a multimeter and compare to the manufacturer's specification.
  4. Check for continuity and short to ground on the control circuit between the PCM and the valve, repairing any faults found.
  5. Inspect the fuse and relay for the fuel shutoff valve circuit and replace if faulty.
  6. If the circuit and valve test good, diagnose the PCM driver circuit or substitute a known-good PCM for testing.
  7. Clear the code and perform a road test to confirm the repair, ensuring the code does not return.

Before replacing the fuel shutoff valve

  • A low voltage code on the control circuit often points to a short to ground in the wiring rather than a failed valve, so always inspect the harness first.
  • The fuel shutoff valve may only be commanded during specific conditions such as a crash signal or ignition off, so the valve might test fine statically but fail under load.
  • Corrosion inside a connector can cause intermittent low voltage codes that do not appear during a simple resistance check, so wiggle-test the harness while monitoring live data.
  • Aftermarket remote starters or alarm systems tapped into the fuel pump circuit can backfeed and set this code, so check for non-factory wiring.
  • This code does not always mean the valve itself is defective; a poor ground connection at the PCM or chassis can also cause a low voltage reading on the control circuit.

Can I keep driving with P2666?

If the vehicle is running normally and the only symptom is the check engine light, you can drive cautiously to a repair shop, but avoid hard acceleration or towing. If you experience stalling, difficulty starting, or a fuel smell, stop driving and have the vehicle towed to prevent safety hazards.

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 all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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