P0402 on Mazda: How to Diagnose & Fix
Exhaust Gas Recirculation Flow Excessive
4 Mazda models · 4 documented issues · $60-$800 repair
P0402 on Mazda by model: symptoms, diagnosis and fix
EGR valve and intake passages clog with carbon causing rough idle, hesitation, and check engine light. Carbon accumulation in EGR passages restricts flow.
Common Symptoms
- Rough idle
- Hesitation on acceleration
- Check engine light
- Failed emissions test
- Poor fuel economy
How to Fix
Remove and clean EGR valve. Clean EGR passages in intake manifold with carburetor cleaner and wire brushes. Replace EGR valve gasket.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- CRC 05379 Carburetor and Throttle Body CleanerOEMCRC 05379
Use only according to the label, with the engine cool
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Owner tips & cautions
- TipClean EGR passages every 60k miles as preventive maintenance — soak with carb cleaner and use pipe cleaners
The KL-DE V6 EGR system is highly prone to carbon clogging. Soot accumulates inside the EGR valve diaphragm and inside the EGR passages cast into the throttle body and intake. When the valve sticks open, exhaust gas enters at idle and produces a rough, surging, or stalling idle with a CEL. Owners report that on the MX-6, P0400 (EGR flow insufficient) is the most common emissions code, and approximately 95% of the time it is a clogged valve or completely blocked EGR ports in the throttle body, not a failed component. Access is poor: the upper intake plenum and throttle body must usually come off to clean it properly.
Common Symptoms
- Rough, surging, or hunting idle
- Stalling at stops or when cold
- Check engine light with P0400-series code
- Failed emissions / smog test for high NOx or EGR flow
- Hesitation or sputter during light acceleration
How to Fix
Remove the EGR valve and clean the diaphragm and pintle with carb cleaner, then snake out the EGR passages in the throttle body and intake plenum (this is required if cleaning only the valve does not clear the code). Replace the EGR gasket on reinstall. A new OEM valve is typically only needed if the diaphragm is torn or the electrical solenoid fails.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Fel-Pro 70714 EGR valve gasketOEMFel-Pro 70714
New valve-to-manifold gasket after the EGR valve is removed for the 1996-1997 KL-DE diagnostic/cleaning branch Fitment/availability: The inspected direct page identifies Fel-Pro 70714 as a valve-to-manifold EGR gasket, showed $5.89 and A…
- CRC 05078 throttle-body and air-intake cleaner, 12 ozOEMCRC 05078
Cleaning carbon/varnish from removed compatible throttle-body and intake surfaces during the confirmed clogged-passage repair Fitment/availability: The inspected direct page identifies CRC 05078 throttle-body and air-intake cleaner, show…
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Sources for this issue (3)
The SkyActiv 2.5L engine in third-generation Mazda6 models uses a cooled EGR system that is prone to carbon buildup and coolant leaks. The EGR valve and cooler accumulate carbon deposits over time, restricting flow and causing rough idle and reduced performance. Additionally, the EGR cooler gaskets can leak coolant into the intake or externally, creating a potential overheating risk.
Common Symptoms
- Rough idle
- Check engine light
- Coolant smell from engine bay
- Reduced power and hesitation
- Slow coolant level drop
How to Fix
Remove and clean the EGR valve and passages with carburetor cleaner and a wire brush. Replace the EGR cooler gaskets. If the EGR valve is stuck or damaged, replace it. Mazda issued TSB 01-018/17 for EGR-related issues. Use top-tier fuel and consider an occasional Italian tune-up (sustained highway driving) to help reduce carbon buildup.
Sources for this issue (1)
The 3.0L Tribute uses a differential pressure feedback EGR (DPFE) sensor plumbed to the EGR tube by two short rubber hoses. The sensor's internal element degrades and the hoses crack or fall off, so the PCM sees no measurable flow and sets P0401 (insufficient EGR flow); a stuck or electrically failed EGR vacuum regulator solenoid sets P0403, and a carbon-plugged EGR passage in the intake sets P0401/P0402 as well. This is an emissions-inspection failure item on a large share of surviving Tributes. The common shop error is condemning the EGR valve itself - technicians on Tribute and Escape threads repeatedly find the actual fault is the DPFE sensor, its rubber signal hoses, or carbon blocking the EGR port, and the replaced valve does not clear the code.
Common Symptoms
- Check engine light
- Failed emissions or state inspection
- Rough idle or light surge
- Occasional hesitation under light acceleration
How to Fix
Inspect both DPFE hoses for heat damage, verify the sensor signal and clean the EGR passages before replacing parts. The sensor design and calibration vary across the long year range, and an EGR valve or DPFE sensor will not repair blocked passages or a damaged hose, so no single product is approved.
Sources for this issue (3)
P0402 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0402 mean on a Mazda?
P0402 stands for "Exhaust Gas Recirculation Flow Excessive." P0402 means the Exhaust Gas Recirculation (EGR) system is flowing too much exhaust back into the intake. The EGR system intentionally routes a small amount of inert exhaust gas into the engine to lower combustion temperatures and reduce nitrogen-oxide emissions, but the flow must be metered precisely. When the PCM determines the flow is excessive — often because the EGR valve is stuck open or letting gas through when it shouldn't — it sets this code. Too much EGR can cause rough idle, stalling, hesitation, and a check engine light. On Mazda it is documented across 4 models: 626, MX-6, Mazda6, Tribute.
What are the most common causes of P0402?
The most common causes of P0402 are: EGR valve stuck open or not closing fully, Failed or sticking EGR valve diaphragm/solenoid, Carbon buildup holding the EGR valve open, Faulty EGR position or differential pressure (DPFE) sensor, Leaking EGR valve gasket or pintle seat, Vacuum control or solenoid fault commanding EGR open, Wiring or connector problems in the EGR control circuit. The specific cause varies by vehicle.
How much does it cost to fix P0402 on a Mazda?
Published repair estimates on Mazda range from $60 to $800 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0402 on a different make?
View P0402 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.