Injector Learning / Calibration

Applies to all known Boxer Diesel models, Euro 4/5/6.
Injector learning (micro quantity calibration) procedure is supposed to improve injection accuracy of small injections, improving vibrations, noise, fuel economy etc. The ECU measures engine speed changes, derives learning values and uses them from there on.

Tiny fuel injections, achieved through very short pulses, are especially sensitive to mechanical wear inside injectors. Remember, the ECU does not know how much fuel is actually being sprayed into the cylinders. However, by measuring acceleration (crankshaft speed changes) after at each cylinder’s power stroke, it can adjust injection pulses to achieve a balance across cylinders.

Normally, a power stroke consists of two or three individual injections, main injection always being the largest one. For micro quantity calibration, the software does things differently. It divides the necessary fuel to hold engine speed into more and evenly small injections so that only short pulses matter and differences in injected amounts can be compensated.
The entire procedure is done in two ways:

  1. Automatically by ECU when idling (~800 rpm), for example at traffic light stop. There’s a delay of 5 seconds (stock calibration) till commencement. Then the actual process takes roughly a minute to complete. In this auto-mode the software only goes through first 4 pressure levels. ECU will try again later if it could not finish.
  2. Compulsory using Subaru dealer software (open source solution is planned). In addition to auto-mode, it uses higher common rail pressure, revving the engine up to 1,200 rpm at 5th pressure level which is not acceptable in auto-mode.

Injector Learning Chart

Either way, the operation causes distinct engine sound due to special injection patterns, easy to recognize. Also altering common rail pressure to the next pressure level causes noise to change.

You can use logging (Subaru specific protocols) in order to monitor related parameters:

  • injector learning status (ON/OFF)
  • injection quantity learning values [ms] (4 cylinders times 5 pressure levels = 20 values; all zeroes means learning has not been completed successfully)
  • mileage after last learning [km]
  • mileage after injector replacement [km]

As usual, all relevant values are being saved into EEPROM.

Automatic Injector Learning Intervals

In theory, ECU wants to do automatic injector learning at these predefined intervals:

# Odometer
1 50 50
2 200 150
3 350 150
4 950 600
5 1,550 600
6 4,550 3,000
7 7,550 3,000

Confirmed by disassembly from Euro 4/5/6 software. As you can see, the interval is being increased up to 3,000 km.

Above odometer values are theoretical because:

  • For the ECU mileage after last learning matters, not any absolute odometer value.
  • If conditions are not met, learning process is being delayed, trying again at next occasion, increasing all further odometer numbers.
  • ECU internal odometer is not very precise, it will drift off from combination meter odometer over time.

Injector Learning Conditions

Basically, engine must be warm, around 80°C coolant temperature. Lots of parameters must be within pre-defined ranges (fuel temperature, accelerator not depressed, battery voltage 12..15 Volts, …).

Video Links

Courtesy of contributors posting their videos.

Automatic learning



  • Adjusting internal variable “mileage after last learning”, i.e. setting to 3000+ km triggers automatic calibration ASAP.
  • Adjusting ECU odometer, i.e. to re-synchronize with dashboard value.

Other Brands

Many other car brands are based on Denso diesel software.

Mazda SkyActiv-D 2.2 (CX-5)

  • Piezo injectors!
  • 20x “Fuel injection learning value …” [µs] (FI_LRN_{pressure level, cyl}) monitoring PIDs.
Automatic learning

3 pressure levels (350, 650, 950 bar = 5080, 9430, 13780 psi)
Learning interval up to 2,000 km.

Compulsory learning

2 additional pressure levels (1400, 1970 bar = 20310, 28570 psi), at increased engine speed.


2 responses to “Injector Learning / Calibration

  1. here you can find my video of Compulsory Injector Learning:


  2. Hi,
    My 08 euro 4 outback sometimes calibrates every day – even when all 4 pressure learning stages seem to go through properly. Usually the engine runs with quite loud tapping – when not completely warm and under load. After compulsory cycle done by the service station the engine runs smooth like new – until it does automatically learning cycle – most often after it, it starts to run bad when cold and quite sluggishly when warm. The service station guys don’t know what could it be. Have you any idea, what’s happening?.


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