The P0402 code on your 2020 Ford F-150 indicates the PCM has detected excessive exhaust gas recirculation flow. Too much EGR flow can cause rough idle, hesitation, and poor performance—the opposite problem of insufficient flow.
F-150 Engine Options and EGR
The 2020 F-150 offers several engines: 2.7L and 3.5L EcoBoost V6, 3.3L V6, and 5.0L V8. Each has specific EGR system configurations. EcoBoost engines use electronically controlled EGR valves integrated with turbo operation. Excessive flow disrupts the air-fuel mixture and combustion efficiency.
Causes of Excessive EGR Flow
An EGR valve stuck open is the most common cause. Failed valve seals or worn internals prevent proper closure. A faulty EGR position sensor may report the valve closed when it's actually open. On vacuum-operated systems, a stuck-open vacuum solenoid keeps the valve open continuously.
Symptoms of Excessive EGR
You may notice rough idle, especially when stopped. The engine may hesitate during acceleration as excess exhaust gas dilutes the air-fuel charge. Fuel economy typically suffers. In severe cases, the engine may stall at idle when the EGR valve is stuck wide open.
Diagnosis and Repair
Use Ford IDS to monitor EGR valve position. Command the valve closed and verify it responds. Inspect the valve for carbon holding it open or internal damage. Check vacuum lines and solenoids on applicable systems. A stuck-open valve requires replacement—cleaning rarely fixes mechanical failures.