P3400 code meaning
Cylinder Deactivation System Bank 1
Powertrain system Generic code P34xx codes Check engine light
What P3400 means
P3400 is the bank-level verdict: the engine computer has concluded that cylinder deactivation on bank 1 as a whole does not behave as commanded, without blaming a single circuit. Makers fill it differently. On the 2019 LT4 Corvette, GM compares a manifold pressure model with all cylinders firing against the same model while cylinders are off; 100 failed samples out of 200 give a Type B code. Mazda's 2.5 l four-cylinders store it when a deactivation oil control valve is clogged, for example by plastic from the filter wrapper (SA-061/20). In Honda's VCM V6 it stems from a rocker arm oil pressure switch, and the Hemi Ram 1500 got a PCM update for it. Bank 2 is P3497. The lamp comes on; misfires or rough running may follow.
P3400 at a glance
- Check engine lightYes, usually on
- Emissions testCan fail
- Limp modeNot expected
- Repair difficultyHard
- Typical labor0.5 to 12 hours
- Clears after repairAfter a drive cycle
Symptoms of P3400
- Check engine lamp on
- Rough idle or misfire codes on the deactivating cylinders
- Ticking or clattering from the valve train
- Reduced-cylinder mode no longer used, higher fuel use
Common causes of P3400
- Most likelyDeactivation oil control valve or its screen clogged by debris
- Most likelyLow oil level, wrong grade or overdue oil change
- PossibleSwitchable rocker arm or lifter broken, dislodged or not latching
- Less likelyOil pressure too high on cold start, e.g. weak relief valve spring
- Less likelyEngine control software needing an update
Check the most likely causes first. Replacing parts by guesswork is the most expensive way to clear a code.
Parts involved
Cylinder deactivation solenoidLifterOil control valve
What each part of P3400 means
| P | Powertrain system: engine, fuel system, ignition, emissions and transmission. |
| 3 | Mixed range: generic and manufacturer-specific codes. |
| 4 | Area: auxiliary emission controls (catalytic converter, EGR, EVAP). |
| 00 | The exact fault in that area. |
What to do next
- Note P3400 and any other codes stored with it: several codes together often point to one cause.
- Check for loose connectors and damaged wiring around the parts the code names.
- Check open recalls for your car: some faults are fixed for free by the dealer. Enter your VIN.
- Clear the code only after the repair. If it comes back, the fault is still there.
Buying a used car? Scan it for stored codes before you pay. A recently cleared memory can hide a problem.
Questions about P3400
What does P3400 mean?
P3400 means "Cylinder Deactivation System Bank 1". P3400 is the bank-level verdict: the engine computer has concluded that cylinder deactivation on bank 1 as a whole does not behave as commanded, without blaming a single circuit. It is a generic code, so it means the same on every make.
Is it safe to drive with P3400?
Usually yes, for a short time, if the check engine light is steady and the car drives normally. If the light flashes or the car runs badly, stop and have it checked.
Will P3400 fail an emissions test?
Yes, it can. P3400 is emissions-related, so most inspection programs fail a car while it is stored or while the check engine light is on.
How hard is P3400 to fix?
Difficulty: hard. A typical repair takes 0.5 to 12 hours of work. This is a job for a workshop.
Will P3400 clear itself after the repair?
After the repair the car has to complete a drive cycle (a mix of city and highway driving) before the test runs again. Until then the readiness monitor shows "not ready", which can fail an inspection.