1998 Chevrolet Silverado 6.5 Diesel P0101, P0401, P0236, P1409 Emissions Fault Codes - Diagnosis and Fixes

Model: 98 chevrolet diesel Fault Code: P0101 Posted: 2008-04-20 18:36

I own a 1998 Chevrolet Silverado 6.5L diesel engine and am currently experiencing persistent diagnostic trouble codes: P0101 (Mass Airflow Sensor Malfunction), P0401 (Exhaust Gas Recirculation System Flow Fault), P0236 (Fuel Pump Control Circuit Issue), and P1409 (EGR Valve Performance Problem). These codes are clearly related to emissions systems. I recently removed the EGR valve and manually tested its vacuum operation—functioned properly. I also cleaned some carbon buildup from the intake manifold, and while the check engine light remained off for approximately 50 kilometers after code clearing, it reactivated shortly afterward. Given this behavior, I'm wondering whether the issue lies with the Mass Airflow (MAF) sensor or EGR position sensor—specifically where to locate them and how to properly test each. Any guidance on troubleshooting these components would be greatly appreciated. Thanks in advance for your insights.