P1402 — Flap fault | EGR throttle valve fault

Causes

• Carbon buildup causing flap to stick or bind
• Faulty EGR flap/throttle actuator (motor or stepper)
• Failed or out-of-spec EGR position sensor/feedback potentiometer
• Broken, corroded or loose wiring/connectors to the actuator or sensor
• Vacuum supply or vacuum solenoid failure (if vacuum-operated unit)
• Clogged EGR passages or cooler preventing movement

Symptoms

• Malfunction Indicator Lamp (MIL) illuminated
• Poor idle quality, roughness, or stalling
• Hesitation or reduced engine power under load
• Reduced fuel economy
• Failed emissions test (increased NOx/smoke)
• Intermittent limp-home mode or derated performance

What to check

• Read and record freeze-frame and all stored DTCs with a capable scan tool
• Use live-data to monitor EGR target position vs actual position while commanding EGR open/close
• Perform an active test: command the EGR flap/throttle and observe movement and feedback
• Visually inspect EGR valve, flap, linkage and surrounding area for carbon buildup or mechanical damage
• Inspect wiring harness and connectors for corrosion, damage, or poor connection; wiggle test while monitoring signal
• Check for correct power supply and ground at the actuator and position sensor

Signal parameters

• EGR position/feedback sensor: typically 0–5.0 V (varies by design). At rest values often in low-to-mid range; target vs actual should track closely when commanded
• Actuator control: may be PWM, stepper steps or applied voltage — duty cycle or step count should change when commanded by scan tool
• Typical sensor reference/return circuit voltages: reference supply ~5 V, ground ~0 V (verify at connector)
• If applicable, motor coil resistance: compare to manufacturer spec (expect continuity; open/short indicates fault)
• If vacuum-operated: vacuum line should hold vacuum and vacuum solenoid should switch vacuum on/off when commanded

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