DTC P0204: Injector No. 4 Control Circuit: Description
WARNING: This page is about a different car, the 2001 Saturn LW200, 2001 Saturn L200, and 2001 Saturn L100. However, it is still accessible from the selected car via links, so may be relevant.
PCM has 4 injector driver circuits controlling each injector. PCM monitors current at each injector driver circuit by measuring voltage drop through a fixed resistor and is able to control the driver circuit. Current through each driver can rise to a peak of 4 amps to quickly open the injectors and can drop to one amp to hold injectors open. This called the peak and hold. If current cannot reach a 4 amp peak, DTC will set. DTC will also set if an injector driver is shorted to voltage.
Injector circuit is continuously checked when engine is running.