P2B04: Cylinder 5 Injection Pulse Performance
What to do
Drivable, but this is an early warning worth taking while it is cheap. One cylinder is drifting away from its neighbours — commonly a clogging or leaking injector — and the module is running out of trim to hide it. Injector cleaning or one injector now is the good outcome; ignored, unequal cylinders wash bores, dilute oil and load the aftertreatment with what they leave unburnt.
What this code means
Cylinder 5's injection pulse correction is not performing as expected.
A modern engine trims every injector individually, and this code is one cylinder's trim complaining. Injectors leave the factory with real manufacturing spread, and they age at different rates in different cylinders. The module measures each cylinder's actual contribution — through crankshaft speed fluctuation, pressure sensing or exhaust feedback, by design — and adjusts each injector's pulse to even them out. Pulse performance out of range means one cylinder's correction is not achieving what it should.
This is the precision layer, so the symptom is often refinement rather than breakdown. A slightly rough idle, a diesel that has turned knocky and clattery, marginal smoke, uneven running just off idle — the kinds of complaint that survive a basic inspection because nothing is failed, one cylinder is merely wrong.
The code names the cylinder, which is most of the diagnosis. Swap that cylinder's injector with a neighbour and see whether the code follows: if it moves, the injector is the problem; if it stays, look at what is unique to the cylinder — compression, its wiring, carbon on its valves. That one test separates an injector bill from a deeper one.
Likely causes
Start here
- Clogged fuel injectors · moderate
- Leaking fuel injector · specialist
Less common
- Failed fuel injector · specialist
- Low fuel pressure · specialist
- Corroded or loose connector · specialist
Symptoms
Components involved
Information, not instruction
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