U0306: Software Incompatibility With Fuel Injector Control Module
What to do
Nothing is broken, but there is one thing to insist on when this is fixed, and it is easy to miss.
This code means two of the car's computers are running software that does not belong together. It is a programming job, not a repair.
The reason it matters more than most is the injectors. Each diesel injector on your engine carries its own calibration code, printed on it and typed into the computer, because no two injectors deliver exactly the same amount of fuel. The computer applies those corrections on every single injection.
A software mismatch can leave those corrections stored in a form the other computer reads differently — so the engine runs with corrections that do not match the injectors actually fitted. You may notice an uneven idle, a harder knock from one cylinder, some smoke, or worse economy, and there may be no other fault code at all.
So when the software is put right, ask specifically for the stored injector codes to be read back and checked against the numbers printed on the injectors. It takes five minutes, it is skipped almost every time, and it is the difference between a repair that is finished and one that is merely quiet.
What this code means
A module is running software that does not belong with the fuel injector control module's. See U0300 for the family and U0301 for why the named module is not the accused.
There is one consequence here that is worth more than the rest of the page, and it connects to the injector calibration argument at P2690.
A common-rail injector carries an individual calibration code, printed on its body and entered into the module against the cylinder it is fitted to, because manufacturing tolerances make two identical injectors deliver measurably different quantities. The module applies those corrections on every injection.
The format and meaning of those codes is defined in software. So a module pair at different calibration levels may store, exchange or interpret the correction values differently — and the result is not a fault the vehicle can see. It is an engine running with per-cylinder corrections that no longer correspond to the injectors fitted.
That produces the P2690 failure without the P2690 code: uneven idle, a harder knocking note from one cylinder, smoke, worse economy, and over time a cylinder over-fuelled by a correction meant for a different injector — a slow risk to the piston and valves rather than an immediate one, but real.
So the instruction is specific and it prevents a repeat. After this is resolved, have the stored injector calibration codes read back and compared against the codes printed on the injectors themselves. A software correction can leave the values intact, migrate them, or lose them, and only reading them back tells you which — a five-minute check that is skipped almost every time and that turns an uncertain repair into a settled one.
Likely causes
Start here
- Software updated on one module only · specialist
- Incorrect module configuration after replacement · specialist
- Injector fitted without entering its calibration code · specialist
Less common
- Second hand module locked to another vehicle · specialist
- Interrupted module programming · specialist
- Software calibration out of date · specialist
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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What makes one worth reading:
- The car — make, model, year and engine. The same fault behaves differently on each.
- What you measured, not only what you replaced.
- What actually fixed it — or that nothing did, which is worth knowing too.
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