P3400 on Mazda: How to Diagnose & Fix
Cylinder Deactivation System Bank 1
1 Mazda model · 1 documented issue · 1 critical
P3400 on Mazda by model: symptoms, diagnosis and fix
On the non-turbo 2.5L Skyactiv-G engine, the cylinder deactivation solenoid can fail at very low mileage, throwing a P3400 check engine light. In a documented 2025 CX-50 case the dealer found metal shavings in the oil filter and oil control valves and, after the code recurred, Mazda advised replacing the cylinder head on a nearly-new vehicle. Note this is currently a low-volume report rather than a confirmed widespread defect.
Common Symptoms
- Check engine light shortly after purchase (as early as 600 miles)
- P3400 fault code
- Metal shavings found in oil filter
How to Fix
Have the dealer scan for P3400, replace the failed cylinder deactivation solenoid(s), and inspect the oil filter and engine oil for metal contamination. If significant debris is present, request cylinder-head or short-block evaluation under powertrain warranty, and document all failures with the dealer to preserve coverage.
Call to confirm they can assess your vehicle and perform the stated work. Search results do not confirm qualification, eligibility or coverage.
What you need to fix it
Only diagnosis- and fitment-reviewed repair parts are linked here.
- Genuine Mazda PYFA-12-360A solenoidOEMMazda PYFA-12-360A
Replace the specifically diagnosed cylinder-deactivation solenoid only after dealer/VIN confirmation Fitment/availability: Indexed direct OEM product page identifies PYFA-12-360A, sale price and Add to Cart, but explicitly exposes no app…
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Sources for this issue (1)
P3400 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 P3400 mean on a Mazda?
P3400 stands for "Cylinder Deactivation System Bank 1." This code indicates the engine control module detected a fault in the cylinder deactivation (variable displacement) system on bank 1, the side of the engine containing cylinder number one. Cylinder deactivation closes the valves and cuts fuel to certain cylinders under light load to save fuel, using oil-pressure-operated control solenoids. When the system can't operate correctly, the module sets this code; you may notice reduced fuel economy, a slight performance change, or a warning light. The most common trigger is low oil level or poor oil pressure. On Mazda it is documented across 1 model: CX-50.
What are the most common causes of P3400?
The most common causes of P3400 are: Low engine oil level or low oil pressure, Clogged or dirty oil passages/lifters, Faulty active fuel management / cylinder deactivation solenoid, Failed deactivating lifter or collapsed lifter, Wiring or connector fault in the solenoid circuit, Sludge from missed oil changes, Faulty oil pressure sensor. The specific cause varies by vehicle.
How much does it cost to fix P3400 on a Mazda?
Repair costs vary widely with the root cause and Mazda model; each issue on this page carries its own estimate where one is published.
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Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.