P026B: requested injection start differs from hardware scheduling

P026B checks agreement between the application software's requested start of injection and the start scheduled by hardware input/output software. The source explicitly describes a timing-only comparison across the relevant cylinders. It is not the same as measuring an injector's actual fuel delivery or current-rise period.

The scheduling record is central

The monitor requires injection commands in the prior engine cycle and usable hardware scheduling information. Dropped pulses, injector electrical faults, injection-controller faults and crankshaft-sensor faults restrict the evaluation. Cold-start strategy must also be inactive.

Failure is eight samples out of sixteen, with one sample each engine revolution and Type A, one-trip reporting. Engine speed therefore affects the elapsed time represented by those samples; they are not a fixed sixteen-second or sixteen-millisecond window.

A numerical limit needs units

The threshold column shows an outside-−5-to-+5 comparison but does not print its unit on the cited pages. This article does not silently assign degrees, time or another unit. A complete numeric test requires the actual calibration/service definition and remains source-review flagged.

Preserve the requested and scheduled start information and associated fault status. Verification should establish agreement during an eligible evaluation. This monitor does not prove a mechanical timing fault or authorize changing injector timing; professional vehicle-specific diagnosis must identify why the software scheduling comparison failed.

Source and applicability

GM 04B, PDF page 1124; GM 04B, PDF page 1125. This explanation covers the documented 2025 monitor. Confirm the vehicle's module, engine and calibration before applying these criteria; the document's vehicle list does not establish this code's applicability to every listed model.