P0402 Code — EGR Flow Excessive Detected (Causes & How to Fix)
Fix OBD‑II code P0402: EGR Flow Excessive Detected. Step‑by‑step diagnosis, repair guide, cost guide, and safety tips.
What Does DTC P0402 Mean?
P0402 on your Powertrain Emissions system means: The engine control module (ECM) has detected that more exhaust gas is being recirculated than the system expects. This usually means the EGR valve is stuck open, a vacuum leak, or a faulty flow sensor, causing too much exhaust to re‑enter the intake.
How to Diagnose and Fix P0402 — Step by Step
- 1
Visual inspection of EGR components
Check for loose connections, cracked vacuum hoses, and obvious carbon buildup on the EGR valve.
- 2
Scan live data for EGR position
Use an OBD‑II scanner to read the EGR valve position sensor while the engine is at idle and at higher RPM.
- 3
Test EGR valve operation
Apply vacuum (or electrical signal on electronic valves) to verify the valve opens and closes fully.
- 4
Check EGR flow sensor (if equipped)
Measure the sensor output voltage or resistance while the valve is commanded open.
- 5
Inspect and clean the EGR valve
Remove the valve, clean carbon deposits, reinstall and retest.
- 6
Replace faulty EGR valve or sensor
Install a new valve or sensor if it fails the functional test.
When to Call a Professional Mechanic
If the valve fails the vacuum test, the flow sensor reads out of range, or the code returns after a clean, you need a professional to diagnose possible ECM issues or internal exhaust leaks.
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