P2491 — EGR Cooler Bypass Control Circuit High Bank 2

Causes

• Open, short to voltage, or high-resistance in the EGR cooler bypass solenoid/actuator circuit (Bank 2)
• Faulty EGR cooler bypass solenoid or actuator (electrical or internal mechanical failure)
• Poor connector pin contact, corrosion, or water intrusion at harness/plug
• Faulty PCM or driver transistor (less common)
• Aftermarket modifications or recent repairs that disturbed wiring or connectors

Symptoms

• Check Engine Light (MIL) illuminated and DTC P2491 stored
• Possible reduced engine performance, rough idle, or increased exhaust temperatures under some conditions
• Poor fuel economy or increased emissions/failing emissions test
• In some vehicles, EGR-related drivability issues (hesitation, stumble) or limp-home behavior

What to check

• Read DTCs with a capable scan tool; record freeze frame and live data for EGR bypass command and feedback
• Visually inspect wiring and connector at the Bank 2 EGR cooler bypass solenoid for corrosion, bent pins, looseness, or damage
• Check battery voltage (12.4–12.7 V) and ground quality before electrical tests
• Backprobe the solenoid connector with key ON (engine off) and compare voltages to expected values and to Bank 1 if available
• Check for other related codes (EGR, temperature, boost, PCM) that may help identify root cause

Signal parameters

• Typical command: PCM may use switched 12 V or PWM duty-cycle control; duty may vary 0–100% depending on design
• Expected idle/KEY ON voltage at solenoid control pin: ~0–12 V depending on commanded state (refer to vehicle-specific manual)
• Expected resistance of EGR bypass solenoid coil (cold): typically 5–50 ohms (vehicle-specific)
• No continuity to battery positive when solenoid is commanded OFF; continuity to ground or switched 12 V when commanded ON depending on circuit design

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