OBD-II Code P0271 — What It Means & How to Fix It

What Does This Error Mean?

P0271 means the fuel injector circuit for Cylinder 4 is reading a high voltage or current signal. The ECM monitors each injector's electrical behavior and expects readings within a normal range. When Cylinder 4's signal reads too high, the ECM sets P0271. This can indicate a short to voltage somewhere in the circuit, a wiring fault, or a faulty injector. Symptoms include rough running, a rich fuel smell, and sometimes a Cylinder 4 misfire code at the same time.

Affected Models

All vehicles 1996+
Common in vehicles with damaged or melted injector wiring
Common in older vehicles with brittle wiring insulation
Common after DIY work near the fuel injector harness

Common Causes

Short to voltage in the Cylinder 4 injector wiring causing an abnormally high signal
Faulty Cylinder 4 injector with an internal electrical fault causing it to stay open
Damaged wiring harness where the insulation has worn through and contacted a voltage source
Faulty ECM injector driver producing the wrong output signal for Cylinder 4
Incorrect injector installed with the wrong resistance specification for the vehicle

How to Fix It

Inspect the Cylinder 4 injector connector and wiring first. Look for any wires that appear melted, bare, or contacting engine components. A wire shorting against the battery positive cable or alternator output can cause a 'high' circuit reading.

Trace the wiring carefully — shorts to power are often hidden under harness tape or conduit.
Unplug the Cylinder 4 injector and use a multimeter to measure voltage at the harness connector with the key on. You should see battery voltage on one terminal (the power feed) and near zero on the other (the ECM control wire). If the control wire also shows battery voltage, there's a short to power in that wire.

The control wire should only go to near zero when the ECM is actively firing the injector.
Test the injector itself by measuring its resistance. Disconnect the connector, probe the two terminals of the injector, and check for the correct ohm reading (typically 10–18 ohms for standard injectors). A much lower reading indicates an internal short in the injector.

An injector with near-zero resistance has an internal short and must be replaced.
Check whether the correct injector was installed. If the vehicle had recent injector work, confirm the replacement injector matches the original specification. Installing a low-impedance injector in a high-impedance circuit (or vice versa) triggers circuit faults.

Your dealer or a parts store can confirm the correct injector spec for your vehicle using the VIN.
If all injector and wiring tests pass, have the ECM tested by a professional with a breakout box. A failing ECM driver stuck in a high-output state is rare but possible. Confirm ECM failure before purchasing a replacement.

Always try to find a reputable ECM repair shop before buying new — rebuilt ECMs often cost far less.

When to Call a Professional

A 'high circuit' fault on an injector that causes the injector to stay open (stuck open) will flood that cylinder with fuel. This washes oil off the cylinder walls and can cause engine damage over time. If you suspect the injector is stuck open — watch for heavy fuel smell, black smoke, or raw fuel smell in the exhaust — get this fixed quickly.

Frequently Asked Questions

What is the difference between P0270 and P0271?

P0270 means the circuit signal is too LOW — often a wiring break, bad connector, or open injector. P0271 means the circuit signal is too HIGH — often a short to voltage or a stuck-open injector. Both affect Cylinder 4, but they point to opposite types of electrical faults.

Can a stuck-open injector damage my engine?

Yes. A stuck-open injector continuously sprays fuel into Cylinder 4. This washes lubricating oil off the cylinder walls, causes hydraulic lock risk if severe, and rapidly ruins the oxygen sensor and catalytic converter. Address a suspected stuck-open injector immediately.

How much does P0271 typically cost to fix?

Wiring repair: $100–$300. Injector replacement: $150–$400 installed. ECM repair or replacement: $300–$1,200+.