P0277 – Cylinder 6 Injector Circuit High

P0277 is an OBD-II trouble code that points to a problem with the fuel injector circuit on cylinder 6. When this code sets, your engine computer is seeing an electrical issue, not just a random misfire. You might notice rough running, poor fuel economy, or a flashing check engine light under load. Left alone, it can lead to internal engine damage. In this guide, you’ll learn what P0277 means in plain language, the most common causes, how a mechanic diagnoses it, and what it usually costs to repair.

What Does P0277 Mean?

P0277 stands for “Cylinder 6 Injector Circuit High.” Your engine control unit (ECU) monitors the electrical signal going to each fuel injector. For cylinder 6, it expects the injector circuit to stay within a specific voltage and resistance range. When the ECU detects that the circuit voltage is higher than it should be, it sets P0277.

In simple terms, the ECU is seeing an electrical problem in the wiring or injector for cylinder 6. That can be from an open circuit, high resistance, or internal injector failure. The result is poor fuel delivery to that cylinder, which can cause misfires and drivability issues.

Quick Reference

• Code: P0277
• Definition: Cylinder 6 Injector Circuit High
• Main area: Fuel injector, wiring, or ECU control for cylinder 6
• Severity: Moderate to severe (risk of engine damage if ignored)
• Common fix: Repair wiring or replace injector #6

Real-World Example / Field Notes

On many trucks and SUVs, especially V6 and V8 engines, I see P0277 pop up after customers complain of a rough idle and poor towing performance. One example was a 5.4L Ford truck that misfired only under heavy load. Scan data showed cylinder 6 misfire counts climbing, and the injector pulse looked off compared to the others. A quick voltage drop test on the injector circuit revealed high resistance in the harness near the valve cover, where the insulation had hardened and cracked from heat. Repairing the wiring and installing a new connector fixed the issue without needing an ECU.

Symptoms of P0277

• Rough idle: Engine shakes or feels uneven, especially at stoplights.
• Misfire under load: Hesitation, bucking, or loss of power when accelerating or towing.
• Reduced power: Overall lack of performance, sluggish throttle response.
• Poor fuel economy: You may notice more frequent fuel stops.
• Check engine light: Solid or flashing MIL, sometimes with misfire codes like P0306.
• Hard starting: Longer crank time or needing to press the gas to start.
• Fuel smell or rough exhaust: Unburned fuel causing a strong exhaust odor and rough exhaust note.

Common Causes of P0277

Most Common Causes

• Faulty cylinder 6 injector: Internal coil failure, open circuit, or excessive resistance inside the injector.
• Damaged injector wiring: Broken, chafed, or corroded wires between the injector and ECU, often near hot engine components.
• Bad injector connector: Loose pins, melted plastic, or corrosion at the cylinder 6 injector plug.
• Poor ground or power feed: High resistance in shared power or ground circuits feeding the injector bank.

Less Common Causes

• ECU driver failure: The internal transistor (driver) that controls injector #6 fails, causing abnormal circuit voltage.
• Aftermarket modifications: Poorly installed performance tunes, harness extensions, or add-on modules affecting injector control.
• Rodent damage: Chewed wiring harness near the fuel rail or intake manifold.
• Previous repair damage: Pinched or stretched wires after intake manifold, head, or valve cover work.

Diagnosis: Step-by-Step Guide

To diagnose P0277 properly, you’ll want a decent scan tool (ideally with live data and Mode $06), a digital multimeter, basic hand tools, and access to a wiring diagram for your specific vehicle. A noid light or an oscilloscope is helpful but not mandatory for DIY work.

1. Confirm the code and check for companions. Scan for all DTCs. Note any misfire codes (like P0306) or other injector circuit codes. Clear the codes and see which ones come back first.
2. Perform a visual inspection. Locate cylinder 6 and its injector. Inspect the harness and connector for broken insulation, oil saturation, melted plastic, or loose fit. Gently tug the wires to check for internal breaks.
3. Check injector connector condition. Unplug the injector. Look for bent, spread, or corroded terminals. Green or white corrosion is a red flag. Clean or replace the connector as needed.
4. Measure injector resistance. With the key off, use a multimeter to measure resistance across the injector terminals. Compare cylinder 6 to other injectors and to spec. An open circuit or significantly higher resistance points to a bad injector.
5. Verify power supply. With the key on (engine off), check for proper voltage at the injector power wire using a wiring diagram. Most systems supply battery voltage to one side of the injector and the ECU controls the ground side.
6. Check control side continuity. With the injector unplugged and the ECU connector disconnected (if accessible), check continuity and resistance of the control wire from the injector to the ECU pin. High resistance or an open circuit will trigger P0277.
7. Wiggle test the harness. While monitoring continuity or live data, gently move the harness around cylinder 6 and along the main injector loom. If readings jump or the engine stumbles, you’ve found an intermittent wiring fault.
8. Use a noid light or scope (if available). Plug a noid light into the injector connector and crank the engine. A weak or erratic flash suggests a control issue from the ECU or wiring. A scope can show pulse width and pattern compared to other cylinders.
9. Check Mode $06 data. Many scan tools will show misfire or injector performance data per cylinder. Compare cylinder 6 to others to confirm it’s the primary problem area.
10. Evaluate the ECU only after other checks. If the injector, wiring, and power/ground circuits all test good, an internal ECU driver fault is possible. This usually requires professional confirmation and ECU replacement or repair.

Pro tip: Before replacing the injector, swap cylinder 6’s injector with another cylinder (if access allows). If the problem and misfire move to the other cylinder, the injector is bad. If P0277 stays on cylinder 6, focus on wiring or the ECU.

Possible Fixes & Repair Costs

Fixing P0277 usually involves repairing the injector circuit or replacing the injector itself. Common repairs include installing a new cylinder 6 injector, repairing or replacing the injector connector, or fixing damaged wiring in the harness. In rare cases, the ECU needs to be replaced or reprogrammed.

Typical repair costs vary by vehicle and access difficulty. A single fuel injector replacement generally runs $150–$450 parts and labor. Harness or connector repairs can range from $100–$350 depending on how deep the wiring is buried. An ECU replacement or repair can cost $500–$1,200+, including programming. Labor rates, engine layout (V6 vs inline), and whether the intake manifold must be removed all affect the final price.

Can I Still Drive With P0277?

You can often still drive with P0277, but it’s not a good idea for long. A misfiring cylinder from an injector issue can dump unburned fuel into the exhaust, which overheats and damages the catalytic converter. You’ll also have reduced power, poor fuel economy, and potentially unsafe performance when merging or towing. If the check engine light is flashing, that’s a sign of an active misfire and you should avoid driving except to get to a repair shop.

What Happens If You Ignore P0277?

Ignoring P0277 can lead to serious consequences: damaged catalytic converters, washed-down cylinder walls, increased engine wear, and in extreme cases, piston or valve damage from prolonged misfiring. Repairing the injector circuit early is far cheaper than an engine or emissions system overhaul.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0277

P0277 shows up most often on multi-cylinder engines where heat and vibration are hard on injector wiring. You’ll commonly see it on Ford and Lincoln trucks and SUVs (F-150, Expedition, Navigator), GM vehicles with V6 and V8 engines (Silverado, Sierra, Tahoe, Suburban), and some Chrysler, Dodge, and Jeep models with V6/V8 powertrains. It can also appear on certain BMW, Mercedes-Benz, and Volkswagen/Audi engines that use individual injector control. Any OBD-II equipped gasoline or diesel engine with a separate injector driver for cylinder 6 can set this code when the circuit goes out of spec.