What does it mean?
The control module compares the injection timing it commands for cylinder 9 with the point at which combustion in that cylinder actually begins, and this code is stored when the real event happens too late by more than the calibrated tolerance. Timing feedback is derived from crankshaft acceleration measured over each firing event, supported on some systems by needle-lift or in-cylinder pressure signals and by the correction values learned for that particular injector.
A late burn wastes part of the expansion stroke, so cylinder 9 produces less torque and burns its fuel less completely than the cylinders around it. The diagnostic requires the deviation to repeat over a number of injection events with the engine warm and the load steady before it commits the code. Many strategies then cap fuel quantity or rail pressure while the fault is active.
Symptoms
- MIL (check engine lamp) on, frequently alongside a misfire or contribution code naming the same cylinder.
- Uneven, shaky idle that is at its worst when the engine is cold.
- Hesitation and reduced pulling power, and on some vehicles a drop into limp mode.
- Longer cranking before the engine catches, especially after standing overnight.
- Higher fuel consumption and grey or white smoke from the exhaust during warm-up.
- On diesels, more frequent particulate filter regeneration because combustion is incomplete.
Likely causes
- Worn, coked or contaminated injector on cylinder 9 whose nozzle needle opens more slowly than the module expects.
- Injector calibration codes missing or wrongly entered after an injector change, so the timing model no longer matches the hardware.
- Rail pressure below the requested value during the monitored window, delaying the moment fuel actually starts to flow.
- High resistance in the injector drive circuit for cylinder 9: corroded terminals, a chafed wire or a poor engine ground slow the current rise.
- Water, air or off-specification fuel in the high-pressure circuit changing how the fuel behaves under compression.
- Stretched timing chain or a slipped crankshaft reluctor wheel, shifting the reference the module times everything from.
- Outdated control module software that does not match the injector variant fitted.
How to fix it
- Read and save the freeze frame, noting rpm, load, rail pressure and coolant temperature at the moment the code set.
- Compare the per-cylinder correction and contribution figures on live data; cylinder 9 should stand out clearly from the group.
- Check commanded against actual rail pressure, since a system-wide pressure shortfall points away from a single injector.
- Inspect the connector and harness for cylinder 9 for corrosion and chafing, and measure solenoid or piezo resistance against specification.
- Run an injector return-flow (back-leak) test and compare cylinder 9 with the rest, then move the suspect injector to another cylinder and see whether the code follows it.
- Check timing chain wear and crankshaft-to-camshaft correlation if several cylinders drift in the same direction.
- After fitting an injector, write its calibration code, run the learning routine, clear the fault and verify on a road test that the deviation stays in tolerance.