Loose or corroded cylinder 7 injector connector (OBD-Codes.com says this was the cause the majority of the time in its author's experience). Open or short in the cylinder 7 injector wiring harness (OBD-Codes.com says this is rare when the wiring has been left undisturbed). Dirty or plugged cylinder 7 fuel injector. Failed cylinder 7 fuel injector. Failed fuel injection control module (FICM) or engine computer (PCM) (listed by RepairPal).

Clean or repair the cylinder 7 injector connector. Repair the open or shorted wiring in the cylinder 7 injector circuit. Clean the cylinder 7 injector if it is dirty or plugged (OBD-Codes.com describes a pressurized injector-cleaner flush through the fuel rail test port on gasoline engines, and says to replace the injector if flushing doesn't fix it). Replace the cylinder 7 fuel injector if testing shows it has failed (RepairPal lists injector replacement as the common repair). Repair or replace the fuel injection control module or engine computer only after the injector, connector and wiring check out.

P0279⛽ Fuel injection / injector circuitStop and fix promptly

P0279: Cylinder 7 Injector Circuit Low (Meaning, Causes, Fixes)

Q: What does P0279 mean?

P0279 means the engine computer has seen a low-voltage condition in the electrical circuit for the cylinder 7 fuel injector, so that injector isn't being controlled properly. OBD-Codes.com says a loose or corroded injector connector is the most common cause, followed by a dirty, plugged or failed injector or an open or short in the wiring, while RepairPal's list of common causes also includes a failed fuel injection control module (FICM) or engine computer. Fuel injectors are small electrically operated valves that spray fuel into each cylinder. OBD-Codes.com explains that on a typical engine the injectors get power through the fuel pump relay whenever the key is on, and the engine computer (PCM) fires each injector by switching its ground on for the right length of time. RepairPal describes the same idea in terms of the PCM's injector 'drivers', special transistors that turn the injectors on and off, and says P0279 sets when the PCM cannot control the injector. OBD-Codes.com describes the cylinder as '#7 cylinder in the firing order'; most manufacturers number cylinders by position rather than firing order, so use the cylinder numbering in the factory service information for your engine to find the right injector. OBD-Codes.com also explains the knock-on effect: a weak injector leans out that cylinder, the oxygen sensor reports lean, the computer adds fuel to every cylinder, and fuel economy drops. The code is generic to OBD-II vehicles, but the repair procedure varies by make. Search interest shows it often comes up on Ford trucks with the 6.0L and 7.3L Power Stroke diesels, so check technical service bulletins (TSBs) for your vehicle.

Q: Can I keep driving with P0279?

Stop and fix promptly. Get it diagnosed soon. RepairPal rates P0279 'Urgent', meaning it can cause severe damage, and OBD-Codes.com says it should be diagnosed and repaired as soon as possible. A cylinder 7 injector that isn't working properly can make that cylinder run lean, which OBD-Codes.com says raises cylinder temperature and can cause detonation (engine knock), rough running and power loss. If the check engine light is flashing, the engine shakes badly, or you smell raw fuel, keep driving to a minimum and have it checked. Fuel systems are under pressure, so don't open fuel lines with the engine running and let the engine cool before working near it.

Reviewed 2026-10-26 · Based on 2 cited source(s)

What P0279 means

Fuel injectors are small electrically operated valves that spray fuel into each cylinder. OBD-Codes.com explains that on a typical engine the injectors get power through the fuel pump relay whenever the key is on, and the engine computer (PCM) fires each injector by switching its ground on for the right length of time. RepairPal describes the same idea in terms of the PCM's injector 'drivers', special transistors that turn the injectors on and off, and says P0279 sets when the PCM cannot control the injector. OBD-Codes.com describes the cylinder as '#7 cylinder in the firing order'; most manufacturers number cylinders by position rather than firing order, so use the cylinder numbering in the factory service information for your engine to find the right injector. OBD-Codes.com also explains the knock-on effect: a weak injector leans out that cylinder, the oxygen sensor reports lean, the computer adds fuel to every cylinder, and fuel economy drops. The code is generic to OBD-II vehicles, but the repair procedure varies by make. Search interest shows it often comes up on Ford trucks with the 6.0L and 7.3L Power Stroke diesels, so check technical service bulletins (TSBs) for your vehicle.

Severity: can I keep driving?

Stop and fix promptly

Get it diagnosed soon. RepairPal rates P0279 'Urgent', meaning it can cause severe damage, and OBD-Codes.com says it should be diagnosed and repaired as soon as possible. A cylinder 7 injector that isn't working properly can make that cylinder run lean, which OBD-Codes.com says raises cylinder temperature and can cause detonation (engine knock), rough running and power loss. If the check engine light is flashing, the engine shakes badly, or you smell raw fuel, keep driving to a minimum and have it checked. Fuel systems are under pressure, so don't open fuel lines with the engine running and let the engine cool before working near it.

Common symptoms

Check engine light on
Engine runs rougher than normal (listed by OBD-Codes.com)
Lack of power (OBD-Codes.com; RepairPal says decreased engine performance)
Worse fuel economy (OBD-Codes.com says a big drop; RepairPal says increased fuel consumption)

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

Loose or corroded cylinder 7 injector connector (OBD-Codes.com says this was the cause the majority of the time in its author's experience)
Open or short in the cylinder 7 injector wiring harness (OBD-Codes.com says this is rare when the wiring has been left undisturbed)
Dirty or plugged cylinder 7 fuel injector
Failed cylinder 7 fuel injector
Failed fuel injection control module (FICM) or engine computer (PCM) (listed by RepairPal)

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

Read all stored codes. Other injector circuit codes (such as P0276 or P0273) appearing together can point to a shared wiring, power or control-module problem rather than one bad injector.
Look up technical service bulletins for your year, make and model.
Find the cylinder 7 injector using the factory cylinder numbering for your engine.
Inspect the cylinder 7 injector connector, as OBD-Codes.com describes: check that it is secure, remove the wire clip and connector, and look for corrosion, pushed-out pins or bent injector terminals. Fix any damage and add dielectric grease before reconnecting.
On a gasoline engine, OBD-Codes.com suggests listening to the injector with a long screwdriver (handle to your ear) while the engine runs. A clear clicking means it is firing; no clicking means no power or a failed injector.
Clear the code and see if it returns. If it comes back after the connector checks out, the circuit or injector needs testing.

Typical fixes

Clean or repair the cylinder 7 injector connector
Repair the open or shorted wiring in the cylinder 7 injector circuit
Clean the cylinder 7 injector if it is dirty or plugged (OBD-Codes.com describes a pressurized injector-cleaner flush through the fuel rail test port on gasoline engines, and says to replace the injector if flushing doesn't fix it)
Replace the cylinder 7 fuel injector if testing shows it has failed (RepairPal lists injector replacement as the common repair)
Repair or replace the fuel injection control module or engine computer only after the injector, connector and wiring check out

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

OBD-Codes.com describes checking for power at the injector harness connector with a voltmeter: no power points to the wiring or connection back to the fuel pump relay. If power is there and the PCM's injector driver is working, the meter shows rapid pulses across the connector terminals, and OBD-Codes.com says the injector should then be replaced
The sources differ: OBD-Codes.com puts loose or corroded connectors first and says shorted or open wiring is rare, while RepairPal's list of common causes is the fuel injection control module (FICM), the injector, the PCM and wiring
Diesel engines (such as the Ford 6.0L and 7.3L Power Stroke) use high-pressure injection systems and, on some engines, a separate injector control module, which work differently from the gasoline layout OBD-Codes.com describes; testing and repair on those is best left to a shop with the right scan tool and factory procedure
The code returns after the connector and wiring have been repaired, or several injector circuit codes set at once

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Can I drive with P0279?

Only as much as you need to. RepairPal rates it 'Urgent', and OBD-Codes.com says to diagnose and repair it as soon as possible because a misbehaving injector can cause rough running, power loss and detonation. If the engine shakes badly or the check engine light flashes, limit driving and get it checked.

Is P0279 always a bad injector?

No. OBD-Codes.com says loose or corroded connectors caused this kind of fault most of the time in its author's experience, and RepairPal also lists wiring, the engine computer and the fuel injection control module. Check the connector and wiring before buying an injector.

What's the difference between P0279, P0280 and P0281?

P0279 is a low-voltage fault in the cylinder 7 injector circuit, and P0280 is the matching high-voltage fault. P0281 is different: it means cylinder 7 is contributing less power than the others, which usually points to a fuel delivery problem rather than a circuit fault.

Why does P0279 show up on Ford 6.0L and 7.3L Power Stroke diesels?

Our sources don't cover those engines specifically. RepairPal lists a failed fuel injection control module (FICM) as a common cause of P0279, and that module is part of how some diesels drive their injectors, so a diesel shop should check it along with the injector and wiring. Look for Ford technical service bulletins for your truck.

Sources

Last reviewed 2026-10-26. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.