P0604 — Internal Control Module Random Access Memory (RAM) Error

What it means

The engine control module has failed its internal RAM self-test: data written to a memory cell does not read back correctly. Adaptive values, fuel trims and the learned throttle position can be lost or corrupted at every start. Symptoms range from a stored code only to rough idle, unstable running and repeated resets of the module.

Likely causes (most common first)

1. Low or unstable supply voltage to the module: weak battery, corroded ground, failing alternator
2. Poor contact or corrosion in the module connectors and their ground pins
3. Voltage spikes from jump starting, welding on the vehicle or disconnecting the battery with the ignition on
4. Moisture ingress into the module housing (footwell, plenum or engine bay location)
5. Corrupted or incorrectly completed software flash of the control module
6. Physical failure of the RAM chip or of solder joints on the module board

Can you drive with it?

Short trips are possible, but the engine may run erratically or stall at any moment, so have the module checked promptly.