Excessive EGR Flow Detected (P0402)
The P0402 code indicates that the Engine Control Module (ECM) has detected excessive exhaust gas recirculation (EGR) flow. This means more exhaust gas is being recirculated back into the intake manifold than intended, which can disrupt the air-fuel mixture and cause performance issues. The EGR system reduces NOx emissions by recirculating a portion of exhaust gases back into the cylinders. Excessive flow can be caused by a stuck-open EGR valve, a faulty EGR pressure sensor, or blocked passages.
1. Most Common Causes
- EGR valve stuck open due to carbon buildup
- Faulty EGR control solenoid or actuator
- Defective EGR valve position sensor (if applicable)
- Blocked exhaust gas recirculation passage
- Faulty differential pressure feedback EGR (DPFE) sensor (common on Ford vehicles)
- Wiring or connector issues in the EGR circuit (short to ground or voltage)
- Failed ECM/PCM (rare)
2. Symptoms You Will Notice
- Check Engine Light illuminated
- Rough idle or engine hesitation
- Poor fuel economy
- Engine knocking or pinging
- Failed emissions test
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm code P0402 and check for additional codes.
Step 2: Visually inspect the EGR valve and vacuum lines for damage or carbon buildup.
Step 3: Test the EGR valve operation by applying vacuum or using a scan tool to command it open/closed.
Step 4: Check the EGR pressure sensor (DPFE) with a multimeter or scan tool for proper voltage readings.
Step 5: Inspect and clean EGR passages if clogged; replace faulty components as needed.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is generally safe for short trips, but prolonged driving may cause engine damage due to detonation or overheating. It's best to diagnose and repair promptly.
How much does it cost to fix?▼
Costs vary from $50 for cleaning to $150 for replacing the EGR valve or sensor, plus labor if done by a shop.
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.