P0403 on Mazda
Exhaust Gas Recirculation Circuit Malfunction
P0403 on Mazda vehicles indicates exhaust gas recirculation circuit malfunction. Au7o has documented this code across 5 Mazda models — most commonly on CX-3, CX-30, CX-5. This emissions code indicates a malfunction in the exhaust gas recirculation (EGR) control circuit. The EGR system routes a small amount of exhaust back into the intake to lower combustion temperatures and reduce nitrogen-oxide emissions, and the computer commands the EGR valve open and closed through this circuit. The code sets when the electrical control signal to the EGR valve or its solenoid is out of the expected range — for example, an open, short, or a commanded change that doesn't produce the right feedback. It generally points to an electrical or wiring problem in the EGR control circuit, or the EGR valve/solenoid itself, rather than carbon clogging alone. Typical repair costs on Mazda range from $150 to $3,000, depending on the specific model and root cause.
Common Causes of P0403
- •Faulty EGR valve or EGR solenoid
- •Damaged wiring or connector in the EGR control circuit
- •Open or short in the EGR control wiring
- •Corroded or loose EGR connector
- •Blown fuse or lost power supply to the EGR circuit
- •Carbon buildup binding the EGR valve
- •Faulty engine control module or driver circuit
P0403 on Mazda by Model
Mazda CX-3(1 issue)
- Rear Brake Noise and Premature Wear2016-2021
CX-3 rear brakes produce excessive grinding, squealing, and scraping noises, often well before pads reach minimum thickness. The rear brake design with integrated parking brake drum-in-hat causes uneven pad contact and noise. Rear pads on the CX-3 also wear faster than expected due to the electronic brake force distribution (EBD) system applying more rear brake bias than typical.
Mazda CX-30(1 issue)
- A/C Condenser Leak2020-2025
The A/C condenser in the CX-30 is prone to developing pinhole leaks from road debris impact and corrosion. The condenser sits exposed behind the front grille with minimal protection. Refrigerant loss causes gradual A/C performance degradation until the system stops cooling entirely.
Mazda CX-5(1 issue)
- Mass Airflow (MAF) Sensor Failure2013-2018
MAF sensor becomes contaminated with dirt or suffers water damage, providing incorrect air intake readings. Causes vehicle to enter "limp mode" with severe performance degradation.
Mazda Mazda3(1 issue)
- Rear Brake Caliper Seizing / Parking Brake Cable Corrosion2010-2025
Rear brake calipers seize due to corroded slide pins and parking brake cable sticking, particularly in northern climates with road salt exposure. The integrated parking brake mechanism within the rear caliper corrodes, causing the caliper to not fully release. Results in uneven pad wear and reduced fuel economy.
Mazda Mazda6(2 issues)
- Subframe and Underbody Rust / Corrosion2003-2015
First and second generation Mazda6 models are prone to severe underbody rust, particularly in the rear subframe, control arm mounting points, and rocker panels. Road salt accelerates corrosion to the point where structural integrity is compromised. Mazda issued TSB 09-007/15 and extended warranty coverage for subframe replacement in some regions.
- Rear Brake Caliper Seizing2009-2021
Rear brake calipers seize due to corrosion of slide pins and the integrated parking brake mechanism. Salt-belt vehicles are especially affected. Causes dragging brakes, uneven pad wear, and premature rotor warping. The parking brake cable can also corrode and prevent full caliper release.
Looking for P0403 on a different make?
View P0403 across all makes →Frequently Asked Questions
What does P0403 mean on Mazda?▼
P0403 stands for "Exhaust Gas Recirculation Circuit Malfunction." This emissions code indicates a malfunction in the exhaust gas recirculation (EGR) control circuit. The EGR system routes a small amount of exhaust back into the intake to lower combustion temperatures and reduce nitrogen-oxide emissions, and the computer commands the EGR valve open and closed through this circuit. The code sets when the electrical control signal to the EGR valve or its solenoid is out of the expected range — for example, an open, short, or a commanded change that doesn't produce the right feedback. It generally points to an electrical or wiring problem in the EGR control circuit, or the EGR valve/solenoid itself, rather than carbon clogging alone. On Mazda specifically, this code is documented across 5 models.
What causes P0403 on Mazda vehicles?▼
Common causes on Mazda: Faulty EGR valve or EGR solenoid, Damaged wiring or connector in the EGR control circuit, Open or short in the EGR control wiring, Corroded or loose EGR connector, Blown fuse or lost power supply to the EGR circuit. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0403 on a Mazda?▼
Repair costs on Mazda range from $150 to $3,000, depending on the specific model and root cause.
Which Mazda models have P0403 documented?▼
Au7o has documented P0403 on 5 Mazda models: CX-3, CX-30, CX-5, Mazda3, Mazda6.