What does it mean?
P1604 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Internal Control Module Driver Error .
Symptoms
- MIL (check engine lamp) on together with circuit codes for whatever that driver controls
- The affected component does not work: no click from a relay or solenoid, a dead injector, a coil that will not fire
- Rough running or misfire, poor starting, or a component such as a fan stuck permanently on
- Reduced power and limp mode
- A fuse that keeps blowing after replacement
- Poor fuel economy or an emissions failure depending on which output is lost
Likely causes
- A shorted actuator winding, such as an injector, ignition coil, solenoid or relay coil, overloading the driver
- Output wiring chafed and shorted to ground or to battery positive
- Water and corrosion in a connector on the driven circuit
- Overvoltage from jump starting or a failing voltage regulator damaging the driver stage
- Poor module ground shifting the driver reference
- Blown fuse or missing supply on the circuit the driver switches
- Internal failure of the driver stage inside the module
How to fix it
- List every stored code first; the companion circuit codes identify which driver is loaded
- Use the scan tool output tests to command each suspect actuator and note which ones respond
- Measure the winding resistance of the suspect actuators and compare with specification; a shorted winding is the usual killer
- With the actuator unplugged, check its control wire for a short to ground and a short to battery positive
- Voltage-drop test the module grounds and verify the supply feeding the driven circuit
- Repair the shorted component or wiring first, clear the code, and see whether the driver fault returns
- Replace and program the module only when the external circuit has been proven good