P0271

Cylinder 4 Injector Circuit Low

Powertrain Fuel and Air Metering Injector Circuit 🟡 Moderate — Fix within a week ⚠️ Drive with Care
💬

What This Actually Means

In plain language — no jargon

The fuel injector for cylinder 4 isn't receiving enough electrical power to open properly, like a solenoid that's not getting enough push to activate. This causes that cylinder to run lean or misfire because fuel isn't being sprayed in.

⚡

Symptoms You May Notice

3 known symptoms for this code
Engine misfire on cylinder 4
Rough idle and power loss
Increased fuel consumption or black smoke
🔬

How Your ECU Detects This

Technical sensor logic and voltage thresholds

The ECM monitors the voltage and current supplied to the cylinder 4 injector coil during operation. It detects when the injector circuit voltage drops below the minimum threshold needed to activate the solenoid valve. A low-voltage condition prevents proper fuel atomization and injection timing.

Voltage & Parameter Thresholds

ParameterNormal RangeFault Condition
Injector Circuit Voltage 11.5-14.5 volts Below 10 volts during activation
Injector Resistance 12-16 ohms Open circuit or short (near 0 or >20 ohms)
🔧

Diagnostic & DIY Fix Guide

Check these in order — from cheapest to most complex
1
Battery and connections
Clean corrosion from battery terminals and check the battery voltage to ensure it's at least 12.6 volts at rest.
2
Injector wiring harness
Inspect the connector and wiring to cylinder 4 injector for loose connections, corroded pins, or damaged insulation and reseat the connector firmly.
3
Fuel injector assembly
Replace the cylinder 4 injector if wiring and connections test good, as internal coil failure is a common cause.
⚠️

When to See a Professional Mechanic

Not all fault codes are safe to DIY

Code P0271 is a moderate fault. You can generally drive to a workshop, but avoid long trips or high-load driving (motorway, uphill towing) until it is diagnosed. If the code keeps returning after clearing, or if you notice the symptoms listed above worsening, do not delay professional diagnosis. Many moderate codes have multiple possible root causes — a mechanic with live OBD data can identify the exact fault more efficiently than part-by-part trial and error.

Safety note: OBD-II codes identify the system or circuit where a fault was detected — they do not always identify the exact failed component. A professional mechanic using live sensor data will diagnose the root cause more accurately than replacing parts based on the code alone.
🔄

How to Clear Code P0271

What happens after you fix the fault

Once the fault is repaired, P0271 can be cleared using any OBD-II scanner. Connect the scanner, navigate to "Clear Codes" or "Erase DTCs," and confirm. The check engine light turns off immediately.

The code will return if the root cause was not actually fixed. The ECM re-detects the fault within 1–3 drive cycles and sets the code again.

✅ Safe to Clear When
  • Fault has been diagnosed and repaired
  • You want to confirm the repair worked
  • Code appeared after a sensor was cleaned
⚠️ Do Not Clear When
  • Preparing for an emissions/PUC test
  • Root cause is still undiagnosed
  • Check engine light is flashing
Emissions test note: Clearing codes resets OBD readiness monitors. Most vehicles need 50–100 km of mixed driving before monitors complete. Do not clear codes immediately before an emissions or PUC inspection.