What does it mean?
Using the pressure trace from cylinder 1 the module works out when combustion actually started, how quickly the heat was released and how much work that cylinder contributed compared with the others. This code is stored when that combustion quality assessment falls outside the calibrated window, so the burn is late, incomplete, weak or otherwise different from what the calibration expects at the current operating point.
It is a result code rather than a circuit code: the sensor is reporting believable numbers, but what it reports about the combustion event is not acceptable. Anything that changes the fuel, the air or the compression in that one cylinder can produce it, which is why the diagnosis must be structured rather than based on guesswork. The module normally corrects fueling as far as it can, then sets the MIL (check engine lamp) and may limit power.
Symptoms
- MIL (check engine lamp) on, usually together with balance, contribution or misfire codes for cylinder 1
- Rough idle with an audible unevenness in the exhaust beat
- Poor cold starting and visible smoke during the first minute of running
- Noticeable loss of power and slower response when accelerating with a load
- Increased fuel consumption and, on diesel applications, louder combustion noise
- Vibration felt at low engine speed and, on some vehicles, limp mode after repeated events
Likely causes
- Injector on cylinder 1 spraying poorly because of a worn or coked nozzle, a sticking needle or internal leakage
- Injector correction values out of range or coding that does not match the injector actually fitted
- Compression loss in that cylinder from worn rings, a leaking or burnt valve, incorrect valve clearance or a head gasket beginning to fail
- Faulty glow plug or weak spark energy in that cylinder, delaying the start of combustion when the engine is cold
- Intake port heavily fouled with soot and oil, restricting airflow into that cylinder only
- Low rail pressure, a restricted fuel filter or air in the fuel affecting the delivery to that injector
- Pressure sensor that has drifted enough to misrepresent the combustion event without setting a range code
How to fix it
- Read the freeze frame and compare live combustion data for all cylinders so the size and direction of the deviation on cylinder 1 are clear
- Check injector correction and balance values and confirm the coding matches the injector fitted to that cylinder
- Measure rail pressure and its stability, inspect the fuel filter and check for air or water in the fuel
- Test the glow plug or ignition components for cylinder 1 if the deviation is worst during a cold start
- Inspect the intake port and the exhaust gas recirculation path for heavy soot that would starve that cylinder of air
- Perform a compression or leak down test on cylinder 1 and compare it with the other cylinders before assuming the injector is faulty
- Repair the cause found, clear the codes and confirm on a road test that the combustion values for cylinder 1 return to the same band as the rest of the engine