Code result
P3403
Cylinder 1 Deactivation Stuck On
Moderate severity
What it means
The engine control module has detected that cylinder 1 remains deactivated when activation is commanded — the deactivation hardware is stuck in the off state. Symptoms include rough running and reduced power.
Is it safe to drive?
Use caution
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.
Most likely causes
Lifter stuck collapsed
highOne of the most commonly reported causes for this code — check this first.
Solenoid stuck in deactivation position
mediumA plausible cause — test and verify before replacing parts.
Carbon or debris buildup preventing free movement
lowLess common, but worth ruling out after the more likely causes.
Related help
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