OBD-II trouble code
P0271: Cylinder 4 Injector Circuit High
The cylinder 4 injector control circuit read higher than expected — normally an open circuit or a short to battery voltage. The cylinder gets little or no fuel, so expect a misfire.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $50 – $1,500
- DIY difficulty
- Intermediate DIY
What does P0271 mean?
P0271 is the opposite condition from P0270 on the same circuit. The engine control module (ECM) fires the cylinder 4 injector by pulling its control wire to ground, and it monitors that wire to confirm the voltage actually drops when it commands a pulse. P0271 sets when the voltage stays high — the ECM tried to pull the circuit down and the circuit did not follow.
Only two things produce that result. The first is an open circuit: a broken wire, a disconnected or corroded connector, or an injector with a broken coil winding means the ECM's ground path connects to nothing, so the voltage never drops. The second is a short to battery voltage: some other power source is feeding the control wire and holding it up against the ECM. Both look identical to the module, and separating them is the first useful step.
That short suspect list is the practical advantage of a high code. A low code can arise from three different faults that all read the same on a scan tool; a high code narrows to open-versus-shorted-to-power, and a continuity check across the injector plus a voltage check on the control wire with the ECM unplugged usually settles it in under half an hour.
With the circuit stuck high, cylinder 4 receives little or no fuel, so a misfire is essentially guaranteed and P0304 commonly appears with it. Unburned fuel and air passing into the exhaust can overheat and ruin the catalytic converter, so this is not a code to defer. Before testing, confirm which physical cylinder your manufacturer calls number 4 — on an inline four it is usually the rearmost cylinder, but on V engines the numbering varies and testing the wrong cylinder wastes the whole diagnosis.
Common causes
- Open circuit in the cylinder 4 injector control wire (broken conductor or corroded splice)
- Open coil winding inside the cylinder 4 injector
- Injector connector unplugged, unlatched, or with a spread or corroded terminal
- Control wire shorted to battery voltage or to another powered circuit
- Chafed harness contacting a powered wire, stud, or terminal
- Loss of the switched power feed to the injectors — a blown fuse or a failed relay
- Rarely, a failed cylinder 4 injector driver inside the ECM/PCM
Symptoms
- Check engine light on, sometimes flashing under load
- Dead or very weak cylinder 4 with a rough, shaking idle
- Misfire codes such as P0304 or P0300 stored alongside
- Marked loss of power and hesitation
- Raw fuel odor from the exhaust
- Poor fuel economy
- Hard starting or extended cranking
Diagnostic steps
- 1.Confirm P0271 and record companion codes. P0270 stored with it suggests an intermittent wiring fault rather than a clean open; P0304 confirms the cylinder is genuinely down.
- 2.Identify cylinder 4 for your engine in the service information before testing.
- 3.Inspect and fully reseat the cylinder 4 injector connector. A connector left unlatched after prior service or a pin that has backed out is a common and free fix.
- 4.Unplug the injector with the key off and measure its coil resistance. An infinite or very high reading confirms an open winding and condemns the injector.
- 5.With the key on and the injector unplugged, confirm battery voltage is present on the feed side of the connector. If it is missing, the fault is upstream — a fuse, a relay, or the feed wire — and replacing the injector will accomplish nothing.
- 6.Disconnect both the injector and the ECM connector and check the control wire end to end for continuity. No continuity confirms an open in the harness.
- 7.With the ECM connector still disconnected, check the control wire for unexpected voltage. Voltage present there means the wire is shorted to a power source that must be located and repaired.
- 8.Once the wiring and injector both test correct, use a noid light or a scan tool injector test to verify the ECM is actually pulsing the circuit before considering the module.
Repair cost
$50 – $1,500
Reseating a connector or repairing a broken wire is often $75-$250, and a simple unlatched connector can cost nothing but time. A single fuel injector is $60-$400 in parts plus 0.5-3 hours of labor depending on access. A blown fuse or failed relay is usually under $100. A failed ECM injector driver is uncommon and runs $500-$1,500 including programming. Diagnosis alone is typically $75-$150.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with fuel injector replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.