Based on information from various sensors, the ECM measures the fuel injection amount. The fuel injector is a solenoid-operated valve and the fuel injection amount is controlled by length of time the fuel injector is held open.
The ECM controls each injector by grounding the control circuit. When the ECM energizes the injector by grounding the control circuit, the circuit voltage should be low (theoretically 0V) and the fuel is injected. When the ECM de-energizes the injector by opening control circuit, the fuel injector is closed and circuit voltage should be peak for a moment.
ECM sets DTC P0271 if the ECM detects that injector (Cylinder #4) control line is short to battery line.
Item
Detecting Condition
Possible Cause
DTC Strategy
Signal check, High
Contact resistance in connections
Short to battery in control circuit
Faulty injector
Faulty ECM
Enable Conditions
Engine start completed
No fuel cut off condition
10.73v < battery voltage < 16V
Threshold Value
Short circuit to Battery
Diagnostic Time
Continuous
MIL ON Condition
3 driving cycle
Temperature
Injector Resistance
20?
13.8 ~ 15.2 ?
When the ECM energizes the injector by grounding the control circuit, the circuit voltage should below (theoretically 0V) and the fuel is iniected. When the ECM de-energizes the injector by opening control circuit, the fuel injector is closed and circuit voltage should be peak for a moment.