1996 Toyota Tercel P0401 and P0402 Fault: EGR System Issues and Diagnosis

Model: 1996 Toyota Tercel Fault Code: P0401 Posted: 2013-09-16 13:19

I own a 1996 Toyota Tercel with a 1.5L EFI DOHC 4-cylinder engine. The vehicle recently triggered the check engine light, displaying fault codes P0401 and P0402. While driving, the engine runs smoothly under normal conditions, but it experiences noticeable stalling or hesitation when idling in Drive or when standing at a stop with the brake engaged. The issue is less severe when parked or in Park. I've already performed spark plug replacement, oil change, and air filter maintenance. After troubleshooting, I suspect the EGR (Exhaust Gas Recirculation) system may be at fault. I've inspected the EGR valve and associated hoses—no cracks were found—and am now considering whether a thorough cleaning of the EGR valve and its associated tubes is necessary. Any advice on diagnosing or repairing this issue would be greatly appreciated, especially given that P0401 (Insufficient Exhaust Gas Recirculation Flow) and P0402 (Excessive Exhaust Gas Recirculation Flow) are linked to EGR performance.