P0287 indicates a cylinder contribution imbalance for cylinder 9, meaning the engine control module has detected that the power output from cylinder 9 is lower than expected compared to the other cylinders.
A stuck, clogged, or leaking fuel injector can cause an uneven air‑fuel mixture, leading to low contribution from cylinder 9.
A weak or failed spark plug, ignition coil, or spark plug wire can prevent proper combustion in cylinder 9.
Low compression due to a worn piston ring, valve seat leak, or timing problem will reduce the cylinder's output.
A leak in the intake manifold or a cracked hose can cause a lean condition for that cylinder.
Rarely, the ECM may incorrectly calculate the contribution balance; this is usually a secondary effect of another fault rather than a primary cause.
In practice, the PCM is almost never the primary cause of a cylinder contribution imbalance. It usually flags the problem after detecting abnormal data from sensors; replacing the PCM without fixing the underlying issue will not resolve the code.
First verify the injector’s operation with diagnostic tests (pulse width, flow test, or swapping). Replacement is warranted only if the injector is proven faulty.
Clearing the code may turn off the Check Engine Light temporarily, but the condition will return if the underlying imbalance persists, and the engine may continue to run poorly.
Yes, a cylinder contribution imbalance can cause incomplete combustion, leading to higher emissions and possible failure of emissions tests.