What does it mean?
P1645 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Internal Control Module Random Access Memory (RAM) Reading Error .
Symptoms
- MIL on, sometimes accompanied by a scatter of unrelated codes
- Reduced power or limp mode; in some cases stalling, long cranking or no start
- Scan tool loses communication with the module or cannot reach it at all
- Learned adaptations, and on some vehicles immobilizer or configuration data, are lost
- Warning lamps flicker and accessories behave unpredictably after a restart
Likely causes
- Unstable or low supply voltage from a weak battery, failing alternator or a bad jump start
- Loose, corroded module power and ground connections
- Water or corrosion inside the module connector or case
- A programming or software update session that was interrupted or corrupted
- Voltage spike from welding on the vehicle, reverse jump starting or disconnecting the battery with the engine running
- Fatigued solder joints or a genuine internal memory failure in the module
How to fix it
- Load-test the battery and check charging output first; this code is very often a supply problem rather than a dead module
- Clean and torque the battery terminals and the module ground points, then confirm with voltage-drop tests
- Unplug the module and inspect the connector and case for water intrusion, corrosion and pushed-out pins
- Clear the code and see whether it returns after a full drive cycle with good voltage
- Check whether the manufacturer has released a software update or reflash for this module
- Repeat any interrupted programming session with a stable power supply connected
- Replace and program/code the module only when the fault persists with the supply side proven good