EngineLightCodes
Powertrain code

P0604 Internal Control Module Random Access Memory (RAM) Error

Severity
Fix soon
Typical repair cost
$110–$1,650
Do it yourself
Shop job
Shop time
0.5–3 hours

P0604 means the module's working memory (RAM) failed its self-test: a value written to a cell does not read back correctly, a built-in hardware test fails, error correction reports faults, or protected memory is written without permission.

How the engine computer detects it

GM's engine module scans the whole RAM within 30 s of start-up and then keeps checking in the background, setting the code after repeated failures with the lamp in the first trip; Ford tests RAM during initialization, the GM gateway with error correction at start (two trips). Unlike most memory codes, P0604 is used the same way by GM, Ford, Chrysler and Saab. Consequences depend on the module: a transmission module goes into limp mode with maximum line pressure and a fixed gear, an engine module may reduce power. The code alone does not say which module set it – the scan tool shows whether it is the engine, transmission, brake or body module.

Written from public technical sources and not yet checked by a mechanic. How we write these pages

Symptoms

  • Check engine light on
  • Limp mode or transmission limp mode
  • Intermittent stalling or starting problems
  • Several module codes at the same time

Common causes

  1. Internal hardware defect of the module (RAM) Most likely
  2. Low voltage, voltage dips or a poor ground or supply at the module Possible
  3. Faulty module software (update available) Less likely
  4. Moisture or corrosion in the module or at its connector Less likely

How to diagnose P0604

  1. Read every stored code with an OBD-II scanner. If misfire or fuel trim codes are there too, fix those first: they often cause this one.
  2. Inspect the parts involved: engine control module, control module power supply, control module ground.
  3. Work through the causes above from most to least likely, cheapest checks first.
  4. Clear the code and drive a full drive cycle to confirm the repair held.

Reading the code

P
Powertrain
0
Generic (SAE) code
6
Computer and output circuits
04
Specific fault

Questions drivers ask

Can I drive with code P0604?

Drive gently and only as far as you need to. The engine computer may limit power to protect the engine, so avoid highways and heavy traffic until it's fixed. If the check engine light starts flashing, pull over.

Will my car pass an emissions inspection with P0604?

Probably not in states that test vehicles with an OBD-II scan: an emissions-related code that keeps the check engine light on is usually an automatic fail. Rules differ by state and county, so check yours.

This page is general information, not a substitute for a professional diagnosis. Repair costs are rough estimates for parts and labor and vary by vehicle and region.