Quote from a DENSO document incl. picture below:
Replacing a Diesel Common Rail Injector:
When replacing a DENSO Diesel Common Rail Injector, marked with a compensation code, it is necessary to register the ID code, printed on the upper part of the injector, with a genuine OEM – or DENSO diagnostic tool, into the electronic control unit (ECU). The injector compensation (ID) code is used to compensate injector production tolerances.
Some vehicles also require Small Injection Quantity Learning.
Subaru’s term for injector compensation or ID code is “injector code“. Dealership diagnostic software (SSM-III, SSM4) has menu items like “Injector Code Display” and “Injector Code New Registration (SSM to ECM)”
First off, the engine control unit has no way of measuring actual injected fuel amount, such technology would be expensive for these kind of small fluid quantities. Due to high common rail pressure, even tiny production tolerances result in unwanted injection quantity variations. Obviously, each injector must be registered using its correct cylinder number so the ECU can apply individual adjustments when it is calculating injections. Basically, the ECU accomplishes desired (target) injection quantity by adjusting the duration of injector drive signal.
Since programmed injector codes as well as any other important data is being saved into an extra EEPROM chip, there is no risk of data loss having the car battery disconnected.
Consequences of Wrong or Missing Injector Codes
According to DENSO:
- Knocking noise
- Unstable idle
- Wiggling during driving
- MIL (Check Engine Lamp) on
Cylinder numbers – Quick Reference
As for a quick reminder, looking at the front of the car into engine bay, cylinder numbers are:
towards back transmission 3 4 1 2 car front (radiator etc.)
Getting Injector Codes via QR Code
Although normally this should not be necessary, injector codes can be read from the actual injector parts even when mounted on the engine and inside the engine bay, therefore not easily accessible. Taking a picture using a mirror tool is relatively easy, no need to disassemble any parts:
While the injector code label itself is hidden by the (white) electrical connector, its QR code is visible by default.
Make sure the QR code on the photo is as sharp as possible and has sufficient resolution. At the car I usually just try to get high quality pictures. Later on my computer I simply select the best pic, then scan QR info straight off the computer screen using a smartphone.
Using an image manipulation program (i.e. GIMP, PhotoShop) in order to improve the QR code area can result in much better QR detection. In my case, this was not needed as the app can also detect inverted QR (light code on dark background).
Android app tested: “Barcode Scanner” from F-Droid repository. Check settings → Invert scan.
As an example, the following pic is the extracted and improved QR code portion from above picture. I used these steps in GIMP: crop, perspective correction, grayscale, invert, brightness & contrast . You should be able to scan this:
Scanning captured QR code results in a line of text containing 49 characters:
First 19 chars:
- First four chars
7890match Denso basic part number.
AA020is also found in Subaru part#
- Possibly contains production date 2008-09-11 ?
- Serial# ?
Injector Code Format
Remaining 30 chars is the exact injector code needed for ECU. These chars must be in hexadecimal [0-9, A-F] form as they are transmitted as 15 bytes to and from the ECU:
|Byte index [0..14]||Content|
|0||const, sort of generation ID, verified by ECU:
|1..12||12 payload bytes containing correction data, type int8, for up to 12 pre-defined correction points. Each signed byte must be within range [-125, 125]. In other words, the following five bytes are not allowed:
|14||simple XOR checksum|
Resultant properly formatted injector code (left to right, 4 chars per block):
B300 0000 0000 E9EB EBEC F300 0000 45
Invalid codes will be rejected! Euro 5+ will return NRC 0x31 (request out of range).
Injector code data is not compatible between common rail system generations due to differing correction points! Euro 4 uses fewer points (10) than E5+ (12). Therefore, for example, programming a Euro 5 injector code into Euro 4 ECU will not work and vice versa.
AFAIK, Denso’s own PC diagnostic software has the ability to read from a QR scanner device, Subaru OEM application SSM-III does not – need to type in codes manually.
Protocols needed for injector code display & registration:
- Euro 4: SSM2 via Serial
- Euro 5/6: Extended OBD-II
As far as we know, there is no free/open-source software for this yet.
EcuTek tool probably supports injector coding (up to Euro 5 ?).
Many other car brands are based on Denso diesel software. These often use similar 15 byte injector codes as well. However, injectors and pre-defined correction points usually differ!
Mazda CX-5 (SkyActiv-D 2.2)
Piezo injectors! 15 bytes; first byte:
3C; pressure levels and corrections points differ vs. Subaru.
Mazda terminology: fuel injector code programming, injector correction factors
- 2017-05: additional notes and details
- 2016-04-03: Euro 6