P0402
Exhaust Gas Recirculation Flow Excessive Detected
If your vehicle's onboard computer has flagged the diagnostic trouble code P0402, it refers to a detected anomaly regarding "Exhaust Gas Recirculation Flow Excessive Detected". This systemic engine fault needs a targeted check before symptoms expand.
Driver's Summary
The diagnostic trouble code P0402 indicates an active fault in the exhaust gas recirculation flow excessive detected circuit or component. Typical symptoms include engine stalling at idle, rough idle, poor drivability. This is a moderate-severity fault — plan a repair shop visit within the week to keep it from escalating.
Symptoms
Engine stalling at idle, rough idle, poor drivability
Common Causes
- EGR valve stuck open
- Faulty DPFE sensor (Ford specific)
- EGR vacuum solenoid shorted open
- Carbon buildup keeping valve open
How to Fix
- 1 Clean carbon from EGR valve seat
- 2 Replace stuck EGR valve
- 3 Replace DPFE sensor
- 4 Test vacuum solenoid
Technical Explanation
Code P0402 is confirmed when the ECM's diagnostic algorithm detects a parameter deviation that persists across a defined number of consecutive drive cycles. EGR flow is verified by monitoring changes in MAP sensor readings before and after valve actuation; correct EGR flow produces a predictable pressure drop in the intake manifold that the ECM can measure with precision. The fault remains stored in memory even after the MIL is cleared; it becomes a confirmed DTC after failing two consecutive drive cycles, and the PCM logs a freeze frame record of the engine's exact operating state at the moment of detection.
Is It Safe to Drive?
While the vehicle is typically drivable with P0402 active, avoid towing, aggressive acceleration, or extended highway driving until the fault is resolved. The primary risk is accelerated wear on egr valve stuck open and faulty dpfe sensor (ford specific).
Mechanic's Pro Tip
The most common mistake with P0402 is replacing the sensor without verifying the reference voltage and ground integrity first. Use a scan tool to monitor the sensor's live output; a truly failed sensor shows a stuck, flatlined reading — a sensor that fluctuates but reads slightly off usually indicates a wiring or vacuum issue, not a dead sensor. Always spray electrical contact cleaner on the connector pins before condemning the sensor.
DPFE Sensor: $80 - $150; EGR Valve: $200 - $400