Parts
$200–1200
P0605 — Internal Control Module ROM Error
CAUTIONIs it safe to drive? The ECM failed its read-only program memory test — this is an ECM hardware failure; don't ignore it or mask it with a reset.
What P0605 means
ROM holds the ECM's calibration and operating program — the code that tells the engine how to run. A ROM error means the ECM detected corruption in that program storage. Unlike KAM (learned values), ROM corruption means the engine's core programming is compromised.
Most likely causes (in order)
- ECM failed internally (age, heat, voltage spike)
- Bad flash programming from a failed tune or update attempt
- Physical damage to the ECM board (moisture, corrosion, impact)
- Voltage surge from a jump-start or charging system fault
- Counterfeit or incompatible remanufactured ECM installed
Symptoms you might notice
- CEL on
- multiple system faults
- engine running on safe/failsafe map
- possible no-start
What to check first
Before assuming ECM failure, verify that charging system voltage is correct (13.5–14.7V at alternator with engine running) — chronic overvoltage from a failed voltage regulator can corrupt ECM flash memory repeatedly. Fixing the charging system first prevents the same failure in a new ECM.
Repair cost & difficulty
Labor
1–3 hr
Difficulty
Advanced