OBD codes / P0605
P0605
SeriousInternal Control Module ROM Error
Treat P0605 with caution: the computer's core program is failing its own integrity check, and behavior can range from normal to stalling or a no-start. Keep trips short and essential until it's diagnosed, and insist on power and ground checks before anyone quotes a replacement computer.
What this code means
P0605 means the engine computer failed a self-check of its ROM — the permanent memory holding its core program and calibration data. The module verifies this stored data against a known checksum, and the code sets when they disagree. Like the other ECM internal codes, the honest first steps are cheap: confirm battery and charging voltage, clean the grounds, inspect the ECM connector, and try a battery-disconnect reset, because unstable power can fake an internal fault. If the code persists with clean power, some vehicles can be recovered with a reflash that rewrites the stored program; if the module won't take or hold the flash, replacement with programming is the fix. A ROM fault can also appear after a botched or interrupted reprogramming attempt.
Symptoms you might notice
- Check-engine light that returns after clearing
- Hard starting or no-start
- Stalling or rough running
- Reduced-power / limp mode
What it costs to fix
Varies by vehicle — get it diagnosed.
The repair cost for this code depends too much on your exact vehicle and the underlying cause to quote a meaningful range. Confirm the cause first so you only pay for the fix you actually need.
Diagnose P0605 for my vehicle →Frequently asked
Can I drive with P0605?
Minimally. The module's stored program is failing its self-check, which can mean anything from no symptoms to limp mode or a no-start. Prompt diagnosis is the safe play.
Is P0605 always a bad ECM?
No. Low voltage, bad grounds, and corroded connectors can trigger false internal faults, and some ROM errors are fixed with a reflash. The module is replaced only when it can't be recovered with clean power and fresh programming.
What's the difference between P0604 and P0605?
P0604 is a fault in RAM, the computer's temporary working memory; P0605 is a fault in ROM, the permanent memory holding its program. Practically, P0605 is somewhat more likely to be recoverable with a reflash, while a true RAM failure means hardware.
Why does a replacement ECM need programming?
A new or used module has to be loaded with your vehicle's specific calibration, VIN, and usually immobilizer/security data before the car will run. That programming step is part of the job and part of the cost.
Seeing P0605 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0605 for my vehicleRelated trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0605 from your phone — see our honest guide to the best OBD2 Bluetooth adapters.
Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.