What it means
Cylinder 4 Injector Circuit High: the signal voltage is above the expected range. This affects fueling of the associated cylinders.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
The engine control module switches and monitors the fuel injector circuit for cylinder 4 to control fuel delivery to that cylinder. P0271 means the circuit signal is higher than expected, which can result from a short to supply or another circuit fault; the code alone does not confirm an injector-flow problem.
Common causes
Most likely first.
- Injector circuit shorted to supply
- Wiring or connector fault
- Connector pins corroded - high contact resistance
Symptoms
- Check-engine light
- Rough idle or misfire
- Reduced power
- Increased fuel consumption
How to diagnose it
- Record freeze-frame data and review cylinder 4 misfire counts and available injector command data to establish when the high signal occurs.
- With the ignition off, inspect the cylinder 4 injector connector and harness for loose or corroded pins, damaged insulation, or contact with a power source.
- Using the vehicle wiring diagram, check the cylinder 4 injector circuit for a short to voltage, open, or high resistance.
- Test the injector winding and compare it with the manufacturer's specification.
- If the circuit and injector pass, test the control module injector driver and its connections before condemning the module.
Common fixes
- Repair wiring that is shorted to a power supply or has damaged insulation.
- Clean and secure the cylinder 4 injector connector or repair faulty terminals.
- Replace the cylinder 4 injector if it fails the manufacturer's electrical test.
- Repair or replace the control module only if its driver fails testing with a sound injector circuit.
Can I keep driving?
Limit driving if the engine misfires or runs roughly, because poor combustion can overheat and damage the catalytic converter. Avoid hard acceleration and stop if the misfire becomes severe or the engine loses substantial power.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.