P0604 Code: Control Module RAM Error — Causes & Fix
P0604 means the ECM/PCM failed an internal RAM (random-access memory) self-test — an internal fault in the control module.
- Applies to
- All OBD-II vehicles (any make or model)
- Est. repair cost
- $60 – $900
- Time to fix
- 1–4 hours
What it means
Causes include an internal module failure, corrupted software, or poor power/ground to the module. P0604 is a generic OBD-II code defined in the SAE J2012 standard, so it applies to virtually any 1996-or-newer OBD-II vehicle regardless of make. Fix the underlying fault, then clear the code with an OBD-II scan tool — it will return if the problem isn't resolved.
Symptoms
- Check engine light on
- Poor running, stalling, or no-start
- Other systems affected
How to fix it
- 1
Check power and grounds
1. Inspect ECM power feeds and grounds. 2. Confirm healthy battery/charging voltage.
- 2
Reflash or replace the ECM
1. If supply is good, the ECM may need reprogramming or replacement. 2. Clear the code after repair.
Frequently asked questions
Does P0604 mean a new ECM?
Often, but verify power and grounds first and check whether a reflash resolves it before replacing the module.
Last updated July 19, 2026
Guidance only — always consult a qualified professional or the official service manual before carrying out repairs.