What does it mean?
In the cold start and warm-up phase the module has calculated that the A injection system delivered more fuel than the strategy asked for. During this phase the software already commands generous quantities to get combustion stable in a cold cylinder, and it monitors how much it has to subtract to hold the target. When that subtraction hits its limit while the engine is still cold, this code is stored instead of the general over-delivery fault. The usual explanation is fuel escaping inside the high-pressure circuit, or a rail pressure signal that reads low so the system overcompensates. Because a cold engine burns extra fuel poorly, the excess ends up as smoke, unburnt fuel in the exhaust and, in the worst cases, fuel washing down the bores into the engine oil.
Symptoms
- Heavy black or white smoke on cold start that clears as the engine warms
- Strong fuel smell around the vehicle after starting
- Rough idle and shaking while the engine is still cold
- Engine oil level rising with a diesel smell, which signals fuel dilution
- Higher fuel consumption on short trips
- MIL on and, on some vehicles, more frequent particulate filter regeneration
Likely causes
- Injector leaking internally when cold, with return flow well above specification
- Rail pressure sensor under-reporting, so the system pumps more than needed
- Leaking pressure limiter or relief valve returning fuel to the tank
- Fuel metering or volume control valve that does not close properly when cold
- Worn injector nozzles delivering more than their calibration assumes
- Wrong or missing injector calibration codes in the module
- External high-pressure leak that only weeps when the components are cold
- Faulty coolant or fuel temperature sensor making the module apply an excessive cold correction
How to fix it
- Confirm the fault is tied to cold starts by reading the freeze frame temperatures
- Perform a leak-off test with the engine cold, comparing the return volume of every injector
- Compare actual and desired rail pressure from the first crank and watch whether pressure overshoots
- Verify the rail pressure sensor by comparing the key-on value with atmospheric and by cross-checking against a second data source
- Check the pressure limiter and control valve for excessive return flow
- Confirm the injector calibration codes in the module match the injectors fitted
- Inspect the engine oil for fuel dilution and change it once the leak is repaired
- Verify the coolant and fuel temperature sensors read correctly after an overnight soak, then repair the component the tests condemn