P0402: Exhaust Gas Recirculation "A" Flow Excessive Detected

What does P0402 mean?

The EGR system feeds a small amount of exhaust back into the intake to lower combustion temperature and NOx emissions. Too much EGR, especially at idle, upsets combustion. P0402 is stored when measured flow is higher than expected.

Both references point to an EGR valve that is stuck open or opening too far, often because of carbon buildup, and to problems in the EGR control and feedback parts.

Common symptoms

• Check engine light on
• Rough idle
• Stalling, often when coming to a stop
• Hesitation on acceleration

Common causes

The causes below are the ones commonly seen with P0402. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• An EGR valve stuck open or opening too far, often from carbon buildup
• A faulty EGR control solenoid or vacuum supply problem
• A faulty EGR position or pressure feedback sensor

What to check with a scanner

• If your car reports it, watch commanded and actual EGR in Live data at idle. Actual EGR should be near zero at idle.
• Read freeze frame data to see when the code set.
• Note companion codes such as P0401, P0403 or MAP sensor codes.
• Clear the code and see whether it returns.

How to read and clear P0402 with OBD Master Pro

1. Plug in your adapter. Connect a generic ELM327 (or ELM329) OBD2 adapter to the diagnostic port, usually under the dashboard on the driver's side. Bluetooth Classic, Bluetooth LE, Wi-Fi and USB OTG adapters are supported.
2. Switch the ignition on. Turn the key to ON or start the engine, depending on your car.
3. Connect in OBD Master Pro. Open the app, go to Connection and pick your adapter. Classic Bluetooth adapters connect from the Bluetooth tab, Bluetooth LE adapters from the BLE tab with no pairing needed. Use the generic OBD2 / EOBD profile or your car's brand profile.
4. Read the codes. Open the fault codes screen to see stored, pending and permanent codes. Confirm P0402 is listed and note any other codes, since they often explain the cause.
5. Check the details. Look at freeze frame data, Live data and, where your car supports it, Mode 06 test results (see the checks above).
6. Fix, then clear. After the repair, clear the codes to turn off the check engine light. Clearing also resets the emissions readiness monitors, so drive normally and check the readiness screen before any inspection. Permanent codes cannot be erased with a scan tool; they clear on their own once the car's self test passes.

Tip: you can also look up P0402 and other codes in the app's DTC search without connecting to a car. If your adapter will not connect, use Connection > Share connection log and email it to support. Many cheap ELM327 clones only handle basic engine OBD2, which is all you need for P0402.

When to see a mechanic

Get professional help if any of these apply:

• The engine stalls at stops
• The EGR valve or passages need cleaning or replacement
• Feedback sensors need testing

If you are unsure, a qualified technician can confirm the cause with tests such as smoke testing, pressure testing or scope readings. Clearing a code does not repair the fault.

Related trouble codes

See all OBD2 trouble code guides

Related guides

Check engine light on: what to do · How to read an OBD2 code (P, B, C, U) · Stored, pending and permanent codes and freeze frame · OBD2 readiness monitors explained · OBD2 glossary · OBD2 by car brand