OBD-II Code · Computer
P0604
PCM RAM Error
Severity
high
Left alone, this one tends to take other parts with it.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$400–$1,500
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
PCM random access memory fault.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
- Intermittent issues
Likely causes
- Failed PCM
Read the full diagnostic procedureP0604 means the PCM's internal RAM (working memory used during runtime, not the flash that stores calibration) has failed its diagnostic self-test.
P0604 means the PCM's internal RAM (working memory used during runtime, not the flash that stores calibration) has failed its diagnostic self-test. Unlike P0603 KAM faults, P0604 is rarely a soft fault — RAM either works or it doesn't, and there is no relearn path. Still, start cheapest-first by confirming battery voltage above 12.4V at rest and steady during cranking, because severe voltage sags can momentarily corrupt RAM contents and latch P0604. Inspect the PCM for water intrusion, heat damage, swollen capacitors, or signs of a prior shorted-sensor event (a 5V reference short can take out internal regulators that feed the RAM). Try clearing the code and monitoring whether it returns within one drive cycle; a hard-fail P0604 returns almost immediately. Check that the PCM grounds are tight and clean (under 0.1V drop) and that no aftermarket device is back-feeding voltage onto a sensor signal wire. The expensive misdiagnosis is replacing the PCM without first confirming that no external 5V reference short is present — install a new PCM into a vehicle with a shorted MAP or TPS sensor and you can damage the replacement module within minutes, repeating the failure.
Vehicle-specific patterns2003-2007 GM trucks and SUVs with the E40 PCM occasionally throw P0604 from internal failure, almost always requiring module replacement and SPS prog…
- 2003-2007GM trucks and SUVs with the E40 PCM occasionally throw P0604 from internal failure, almost always requiring module replacement and SPS programming per GM bulletin 04-06-04-039.
- 2004-2008Ford 6.0L Power Stroke and 2008-2010 6.4L Power Stroke set P0604 from FICM/PCM failures aggravated by chronic low battery voltage; Ford TSB 07-14-1 emphasizes battery health before condemning the module.
- 2005-2010Chrysler/Dodge with the NGC module and 2011+ vehicles with the powertrain control module behind the right kick panel show P0604 after coolant leaks from a failed heater core soak the module.
- 2002-2006BMW E46 and E39 with the MS43/MS45 DME show equivalent internal RAM faults from solder fatigue.
Estimated repair$400 to $1,800.
Look up another code
P0604 — frequently asked
What does a P0604 code mean?
PCM random access memory fault.
What causes a P0604 code?
Common causes: Failed PCM.
What are the symptoms of a P0604 code?
Typical symptoms: Check engine light; Intermittent issues.
Is it safe to drive with a P0604 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $400-$1,500.
How do I diagnose a P0604 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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