P0284 indicates that the powertrain control module (PCM) has detected that cylinder 8 is not contributing its expected share of engine power, based on fuel‑trim or power‑balance data. This imbalance is usually caused by an ignition, fuel‑delivery, or mechanical problem that prevents the cylinder from firing efficiently. The code is part of the cylinder‑contribution/balance monitor and often appears alongside misfire codes.
A fouled, cracked, or eroded spark plug can prevent proper ignition in that cylinder, causing a power imbalance.
A faulty coil, poor primary/secondary wiring, or weak spark output will reduce combustion efficiency in that cylinder.
A clogged, stuck‑open, or electrically failed injector can starve the cylinder of fuel or deliver an improper spray pattern.
Compression loss due to worn piston rings, leaky valves, a blown head gasket, or other mechanical damage limits the cylinder’s power contribution.
An air leak near the intake manifold or a faulty gasket can cause an overly lean mixture for that cylinder, triggering the code.
While the PCM can misinterpret cylinder balance data, it is an uncommon cause and should be considered only after all other possibilities are eliminated.
It signals that the engine computer has determined cylinder 8 is not delivering its expected power relative to the other cylinders.
No. PCM failure is an uncommon cause of this code. The problem is typically in the ignition, fuel, or mechanical systems of cylinder 8; the PCM should be replaced only after all other possibilities have been investigated.
Yes. A worn, fouled, or damaged spark plug in cylinder 8 is one of the most frequent reasons the code appears.
Yes. A leak that allows extra air into the mixture for cylinder 8 can create a lean condition and cause the PCM to flag a contribution imbalance.