P0604: Internal Control Module Random Access Memory (RAM) Error
The engine computer found an error in its working memory during a self test, which usually points to the module itself or its power supply.
What P0604 means
Random access memory is the engine computer short term working memory, where it holds live sensor data and calculations as the engine runs. During a self test, the computer writes and reads test values to check that RAM works. If it does not, P0604 sets. RepairPal lists computer failure and wiring issues as the causes, with symptoms such as decreased performance, stalling and a no start. Because the computer relies on RAM for every calculation, a fault can cause sudden and unpredictable behavior, which is why KBB advises against driving with this code even when the car seems normal. Before condemning an expensive module, shops check the battery and charging voltage, test the computer power feeds and grounds, look for corrosion or water damage, and check for software updates or service bulletins. If power and grounds are good and the error returns, the computer is replaced and programmed for the vehicle, including any security or key relearn steps.
Common symptoms
- Check engine light on
- Engine may not start
- Engine stalling
- Reduced performance
- Other module or communication codes
Most common causes
- Failed engine computer
- Low or unstable supply voltage
- Poor ground at the computer
- Water or corrosion damage to the module
- Wiring issue in the computer power circuits
What to check yourself first
Have the battery and charging system tested, since voltage problems can upset computer self tests. Check for signs of water around the computer location, often under the hood or under the dash. Note any other codes stored with it.
Typical fixes and what they cost
| Fix | Typical cost | Note |
|---|---|---|
| Powertrain control system diagnosis | $61-$90 | Checks supply voltage, grounds and software before replacing the module. |
| Replace engine control module (ECM/PCM) | $1,122-$1,192 | RepairPal lists computer failure as the main cause. |
| Electrical diagnosis to find a wiring or connector fault | $122-$179 | For power or ground wiring faults. |
Typical US price ranges for parts and labor, not quotes. Your shop should confirm the cause with a diagnostic before replacing parts.
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Related codes
- P0601 Internal Control Module Memory Check Sum Error
- P0603 Internal Control Module Keep Alive Memory (KAM) Error
- P0606 Control Module Processor
- P0562 System Voltage Low
- U0100 Lost Communication With ECM/PCM "A"