P0403: Exhaust Gas Recirculation "A" Control Circuit

What does P0403 mean?

On many engines the ECM controls EGR with an electric solenoid or an electric EGR valve. It monitors the control circuit, and when the voltage or current is not as expected it stores P0403.

Both references list the EGR control solenoid or valve and its wiring or connector as the common causes.

Common symptoms

• Check engine light on
• Often no obvious symptoms
• Rough idle or hesitation in some cases
• Possible knocking under load if EGR does not work

Common causes

The causes below are the ones commonly seen with P0403. The actual cause can vary by vehicle, engine and mileage, so treat this list as a starting point, not a diagnosis.

• A faulty EGR control solenoid (shorted or open)
• Damaged wiring or a poor connector in the control circuit
• A faulty EGR valve on electric EGR systems

What to check with a scanner

• Inspect the EGR valve or solenoid connector for corrosion or a loose fit.
• Look for damaged wiring near hot exhaust parts.
• Note companion codes such as P0401 or P0402.
• Clear the code and see whether it returns.

How to read and clear P0403 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 P0403 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 P0403 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 P0403.

When to see a mechanic

Get professional help if any of these apply:

• The circuit needs testing with a meter
• The EGR valve needs replacing
• The code returns right after clearing

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