OBD-II Code P0277 — What It Means & How to Fix It

What Does This Error Mean?

P0277 means the fuel injector circuit for Cylinder 6 is reading a high voltage or current signal. The ECM controls the injector by switching its ground circuit — when the Cylinder 6 circuit reads higher than expected, it indicates a short to voltage or an injector fault. A high-circuit fault can cause the injector to stay on longer than it should, flooding the cylinder with fuel. Symptoms include a strong fuel smell, rough running, possibly black exhaust smoke, and a potential Cylinder 6 misfire code.

Affected Models

All vehicles 1996+ with 6 or more cylinders
Common in V6, V8, V10, and V12 engines
More common after poorly done injector wiring repairs
Common in vehicles with cracked or melted injector harness insulation

Common Causes

Short to voltage in the Cylinder 6 injector control wiring
Internally shorted Cylinder 6 injector that draws abnormally high current
Wiring harness damage causing the Cylinder 6 control wire to contact a 12V source
Incorrectly installed injector with a lower resistance rating than the circuit expects
ECM internal driver fault for Cylinder 6 producing a high output signal

How to Fix It

Inspect the Cylinder 6 injector harness for any wires that appear bare, melted, or pinched against power-carrying components. On V6 and V8 engines, Cylinder 6 wiring often runs near the firewall where it can contact battery cables or fuse box wiring.

Run your fingers along the harness carefully — shorts to voltage are sometimes felt as a warm spot on the insulation before a burn mark is visible.
With the key ON (engine off) and the Cylinder 6 injector unplugged, use a multimeter to check voltage on the control terminal of the harness connector. It should read zero or very near zero. If it reads 12V, the control wire has a short to voltage in the harness.

Write down the voltages you find — this information helps a mechanic diagnose the problem faster and saves you money on labor.
Check the injector resistance. Probe the two terminals on the Cylinder 6 injector directly (not the harness). A reading significantly below the normal 10–18 ohms spec — especially near zero — means the injector has an internal short and must be replaced.

An injector with near-zero resistance will stay energized far longer than the ECM intends, causing continuous fuel delivery into Cylinder 6.
Verify the injector part number if any recent injector work was performed on this vehicle. A low-impedance injector installed in a standard high-impedance circuit will appear as a 'high circuit' fault to the ECM because of the different current draw characteristics.

OEM injector part numbers can be verified by your dealer or online using your vehicle's VIN.
If all the above tests are normal and P0277 persists, have a shop test the ECM driver for Cylinder 6 with a lab scope and breakout box. Confirm the ECM is actually the fault before purchasing a replacement — ECMs are expensive and misdiagnosis is common.

Request that the shop show you the scope capture before authorizing ECM replacement.

When to Call a Professional

If the Cylinder 6 injector is stuck open due to a high-circuit condition, the engine is receiving way too much fuel in that cylinder. This washes oil off cylinder walls and risks hydraulic lock in severe cases. If you smell strong raw fuel or see black smoke, stop driving immediately and have the vehicle inspected. ECM driver failures need a shop with proper diagnostic equipment to confirm.

Frequently Asked Questions

What is the difference between P0276 and P0277?

Both codes are about the Cylinder 6 injector electrical circuit. P0276 means the signal is too LOW — typically a broken wire, bad connector, or open injector. P0277 means the signal is too HIGH — typically a short to voltage or a shorted injector.

Is a shorted injector dangerous?

It can be if it causes the injector to stay open continuously. A continuously open injector floods the cylinder with fuel, washes oil off cylinder walls, and in extreme cases can cause hydraulic lock — where liquid fuel prevents the piston from completing its stroke, potentially bending a connecting rod instantly.

How much does it cost to fix P0277?

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