P0402
Exhaust Gas Recirculation Flow Insufficient Detected
Powertrain Emission Controls EGR System Flow 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your engine's exhaust gas recirculation (EGR) system isn't flowing enough exhaust back into the engine to reduce emissions. Think of it like a water recirculation pump that's not pushing enough water back through the system.

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Symptoms You May Notice
3 known symptoms for this code
Check Engine Light illuminated
Rough idle or engine hesitation during acceleration
Increased emissions or failed smog test
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECM monitors EGR flow by measuring intake manifold pressure changes and comparing them to expected values when the EGR valve opens. It uses oxygen sensors and mass airflow data to calculate actual recirculated exhaust volume. When measured flow falls below calibrated thresholds, the fault is triggered.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
EGR Flow Rate 4-8% of intake mass airflow Less than 2% flow detected during EGR operation
EGR Valve Position 0-100% commanded opening correlates to measured flow Commanded position mismatch with actual flow
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
EGR Valve
Remove and clean carbon deposits with carburetor cleaner, or replace if stuck or failed.
2
EGR Passages and Intake Manifold
Remove and scrape heavy carbon buildup that blocks exhaust gas flow pathways.
3
EGR Sensor or Transducer
Test with a multimeter for proper voltage response; replace if readings are erratic or absent.