Fault code P0403 – a step-by-step guide to diagnosing and fixing it

The DTC P0403 indicates that the powertrain control module (PCM) has detected a problem concerning the exhaust gas recirculation (EGR) circuit. For example, a short in the wiring or control solenoid. The PCM controls the EGR solenoid via the control circuit or driver. When the component is turned on, the voltage is expected to be low. When it is switched off, the voltage is usually high or similar to the car battery voltage. The PCM monitors this closely and sets the code when the voltage is abnormal.

• A short or open circuit. This can occur as a result of loose connections, wear, wiring insulation damage, corrosion, and so on. Water can get into the cables or other electrical components, causing them to corrode and affecting the flow of electricity.
• High resistance caused by chafing wires, damage to the car wiring harness, an open circuit, or a blocked EGR valve. The valve can get clogged up if there is a build-up of carbon deposits or soot on the components.
• A leak in the vacuum line. The hoses can deteriorate over time due to extreme heat and become brittle, causing them to crack or break. Leaks will prevent a vacuum-operated valve from opening.
• A problem with the PCM. This is a much less common problem than those listed above, however, it is possible that the control module could have an electrical fault.

• Sometimes the only noticeable symptom of a control circuit malfunction is an illuminated check engine light.
• You may notice that the vehicle is difficult to start or the engine is unstable when idling.
• Ignition problems such as misfiring or knocking may also occur.
• You may also experience a decrease in fuel efficiency and poor acceleration.

• For the diagnosis stage, you can use an OBD2 scanner or similar diagnostic tool to scan the onboard computer for DTCs. Connect the tool via the data link connector port. While doing so, you can also check the computer’s freeze frame data from when the code was set. Once this step is complete, reset the DTCs and take the vehicle for a test drive to see whether the check engine light will come on again. You can verify the fault by scanning the computer one more time.
• Next, inspect the solenoid wires and connector for signs of damage or significant corrosion. Replace any cracked, frayed or melted wires and fix any loose connections. If the contacts of the connector are corroded, you may be able to restore them by cleaning and treating them with a special electric cleaner spray.
• The control solenoid should be disconnected before checking for a short or open circuit. You can measure the voltage and resistance of the EGR solenoid circuits using a multimeter.
• If the device is working properly or the fault is still there after replacing defective parts and clearing the errors, check for vacuum leaks in the system. These can be detected using a smoke machine or other special equipment. It may also be possible to detect a leak by conducting a visual inspection. Replace worn or damaged vacuum components.