Applicable Systems
OBD-II
Symptoms
ECM ROM checksum error; internal read-only memory fault; ECM may not start or run correctly.
Possible Causes
- ECM internal ROM failure
- ECM corrupted firmware
- Manufacturing defect in ROM
Troubleshooting Steps
- Step 1: Attempt ECM reflash with OEM calibration
Reflash succeeds - Step 2: If reflash fails, replace ECM
New ECM starts normally - Step 3: Program new ECM with VIN and calibration
Programming complete - Step 4: Clear all codes and verify
No codes, engine runs - Step 5: Perform drive cycle for relearn
Adaptive values learned
How to Reset
Replace ECM if reflash cannot fix ROM error.
Common Replacement Parts
- ECM (OEM spec, requires programming)
Frequently Asked Questions
- Q: What is ECM ROM vs RAM?
ROM = permanent firmware (can't change without reflash). RAM = working memory (lost on power off). KAM = battery-backed RAM for adaptive values.
Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II