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

P0605 reports an error in the module's program memory (ROM, today flash), found by a checksum or error-correction check at start-up or in the background. Ford is the main user: its engine and transmission modules compare a ROM checksum and set P0605 with the check engine light; the diesel transmission module tests once per trip at start. GM's engine module does not use P0605 and reports the same fault as P0601; the GM gateway (2025) uses it for uncorrectable ROM bit errors with two-trip logic, and GM Europe's 1.6 L engine even assigns it to processor faults of the throttle control. Which of P0601 and P0605 appears is therefore the manufacturer's choice. The usual repair is reprogramming, which restores the memory contents; replace the module only if the code returns.

Medium severity. Can I keep driving?It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

Symptoms

Check engine light on
Possibly starting problems
Transmission limp mode if the transmission module is affected
Reduced power (GM Europe assignment)

Most likely causes

Program memory corrupted by an interrupted reflash
Internal flash or ROM defect
Faulty module software (update available)
Low voltage, voltage dips or a poor ground or supply at the module

What to check, in order

Start with the simplest. You can tick off each step.

Check the battery and grounds
Clear the code and see if it returns
If it is a reference voltage code, disconnect sensors one at a time and see if the voltage recovers
Check whether a software update is available
Do not replace the control module without a full diagnosis

Good to know

Repair difficulty: hard
It can trigger limp mode.
It affects emissions.

What each character of P0605 means

P: Powertrain: engine and transmission
0: Generic code: same on every make
6: Control modules and outputs
05: Specific fault in that system

Frequently asked questions

Can I keep driving with code P0605?

It depends on the symptoms. If the car is running normally you can go to a repair shop; if it goes into limp mode, drive as little as possible.

What causes code P0605?

The most common causes are: program memory corrupted by an interrupted reflash; internal flash or ROM defect; faulty module software (update available).

Related codes

Sources

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.