Computer & output circuits · Powertrain · generic (SAE-defined)
P0604: Internal Control Module Random Access Memory (RAM) Error
P0604 means the engine computer's self-test found an error in its random access memory (RAM), the working memory it uses while the engine is running.
Standard title per SAE J2012 / ISO 15031-6 · Updated 2026-11-07 · By CarWhere Research
How P0604 sets
The powertrain control module (PCM) tests its random access memory by writing and reading back data patterns during startup and operation. If the data read back does not match what was written, the PCM sets P0604. Low or unstable supply voltage can cause a false failure, so power quality is part of the check.
Common causes of P0604
Roughly most likely first; the actual cause depends on the vehicle and needs testing to confirm.
- Internal PCM memory failure
- Low or unstable supply voltage to the PCM
- Poor PCM ground connections
- Water damage or corrosion inside the module
- Corrupted software after a failed update
P0604 symptoms
- Check engine light on
- Stalling or intermittent no-start
- Rough running, hesitation or reduced power
- Erratic gauge or transmission behavior on some vehicles
How P0604 is diagnosed
- Record freeze frame data and all stored codes
- Test the battery and charging system for proper voltage and ripple
- Voltage-drop test PCM power and ground circuits
- Inspect the PCM and its connectors for water intrusion or corrosion
- Check for service bulletins or software updates, and reflash if available
- Replace the PCM only if the code returns with good power and grounds
Typical fixes for P0604
- Repair PCM power, ground or charging-system faults
- Reprogram the PCM with current software
- Replace the PCM and program it to the vehicle
Replace parts only after testing confirms the cause — a code names the circuit or condition that failed a check, not necessarily the faulty part. We don’t publish per-repair prices; for what households actually spend on upkeep, see car repair costs.
Related codes & warning lights
P0604 FAQ
What does code P0604 mean?
P0604 means the engine computer's self-test found an error in its random access memory (RAM), the working memory it uses while the engine is running. The standard definition is "Internal Control Module Random Access Memory (RAM) Error."
Can I drive with a P0604 code?
Driving is not advised beyond reaching a repair facility. A RAM fault can cause the engine to stall or the module to reset while driving, which is a safety concern in traffic.
Can a bad alternator cause P0604?
It can contribute. Excessive voltage ripple or low voltage can corrupt memory tests, so the charging system should be checked before the computer is replaced.
Is P0604 the same as P0601?
No. P0601 points to a problem with the stored program memory, while P0604 points to the working memory the module uses while running. Both are internal module faults.
Keep researching
More computer & output circuits codes
Sources
- SAE J2012 — Diagnostic Trouble Code Definitions (standard code titles)
- ISO 15031-6 — Road vehicles: communication between vehicle and external equipment for emissions-related diagnostics, Part 6: Diagnostic trouble code definitions
- U.S. EPA — Vehicle Emissions Inspection and Maintenance (I/M) programs
- U.S. EPA, 40 CFR 86.1806-17 — Federal onboard diagnostics requirements for light-duty vehicles
General information written by CarWhere Research, not a diagnosis of your vehicle. Manufacturers can add their own sub-definitions and test conditions; confirm with the factory service information for your year, make and model. Before paying for a repair, check NHTSA for open recalls and your warranty booklet: federal law requires an emissions warranty on major emission-control parts such as the catalytic converter and engine computer.