P0605 Internal Control Module Read Only Memory (ROM) Error

Investigate soon

The ECU has logged a fault on P0605. The definition below is the exact wording the standard uses for this code.

Can you drive it? The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.

The definition

P0605: Internal Control Module Read Only Memory (ROM) Error.

P0605 is a powertrain code (the engine or gearbox), defined by the SAE standard - it means the same thing on any make of car, and any generic OBD-II reader will decode it.

What to check first

Cheapest and fastest checks first:

Read the freeze-frame data stored with the fault - engine speed, load and temperature at the moment it logged tell you whether this happens cold, hot or under load.
Check the connector at the part for corrosion, and that it is fully seated.
Clear the code and see whether it returns, and under what conditions.

What actually causes this on a VAG

P0605 is the ECU failing a self-test on its program memory - the part that holds the software it actually runs, rather than the settings and calibration. In plain terms the module is saying it can't trust its own code. On VAG cars it shows up in the same situations as the other internal-ECU faults: after software work, after low-voltage events, or where the module has been damaged by damp. If the fault is genuinely present rather than just logged in history, limp mode or a no-start is common.

Most likely causes, in order

Failed flash, wrong software, or a cloned ECU. If the code appeared straight after a remap, a dealer update, an ECU repair, or a second-hand unit being fitted and 'cloned' to the car, start there. Software written incompletely, or software that doesn't match the ECU's actual hardware, can fail this check. A full, correct reflash for that exact part is the fix, not a new sensor.
Low or unstable supply voltage. Undervoltage during starting, a jump start, a flat battery, or corroded earth straps can all upset the ECU enough to log an internal fault. Have the battery load-tested and the charging output checked, and clean and tighten the main earth points. A scatter of unrelated codes across several modules at the same time is the classic signature of this rather than of a failed ECU.
Water or corrosion in the ECU or its connectors. On many VAG models the ECU sits in the plenum box under the windscreen scuttle, which floods when its drains block with leaves. Take the cover off and inspect for damp, silt and green corrosion on the plug pins. Corroded pins can also be the whole fault on their own, without the ECU itself being damaged.
Genuine ROM failure inside the ECU. Only once power, earths and connectors have been proved good and a correct reflash has been attempted and still fails. At that point the module needs specialist repair or replacement, and either route ends with it being coded and immobiliser-adapted to your car.

Worth knowing: Before you accept 'the ECU has failed', find out whether the fault is showing as present and static, or only stored in history as an intermittent event. A one-off memory error logged during a flat battery or a jump start, on a car that now runs perfectly, is a very different situation from one that returns the moment you clear it and start the engine.

Reading the code is the easy part

A code names the circuit that complained. What tells you why is watching the sensor behind it while the engine runs — and that is where a code reader stops and a diagnostic tool starts.

VAGPULSE reads every module in a VW, Audi, Skoda or SEAT — not just the engine — shows the live measuring blocks behind this fault, gives you the freeze-frame conditions it was logged under, and clears it once you have fixed it. It also does what a generic OBD reader cannot on a VAG: service resets, coding, adaptations, and Stage 1–3 flashing with your original file saved first.

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Common questions

What does P0605 mean?

P0605 means Internal Control Module Read Only Memory (ROM) Error. It is logged when the ECU sees this circuit outside its expected operating window.

Can I drive with P0605?

The engine light will stay on and the car may run in a reduced-power mode. Read the freeze-frame data to see the conditions the fault was logged under.