P0279

Cylinder 7 Injector Circuit Low

P0279 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 7 Injector Circuit Low. It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P0279
Group
Powertrain
System
Fuel/Inj
Severity
Warning (MIL on, possible limp mode)
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What P0279 means

P0279 — Cylinder 7 Injector Circuit Low — is stored when the PCM detects that the voltage or current on the fuel injector control circuit for cylinder 7 has fallen below the manufacturer-specified operating range. The low-circuit reading prevents the injector from receiving a proper drive signal, causing cylinder 7 to run lean or not fire at all. The MIL illuminates immediately and a freeze-frame snapshot is recorded.

Because a cylinder numbered 7 requires at least seven individual combustion chambers, P0279 is exclusive to engines with seven or more cylinders: V8, V10, V12, and inline-8 configurations are the affected layouts. Common real-world platforms include the GM 6.6 L Duramax V8 diesel (LB7, LLY, LBZ), Ford 6.0/6.4/6.7 Power Stroke V8 diesel, GM LS/LT V8 petrol trucks, Dodge/Ram Hemi 5.7/6.4 V8, Audi/Lamborghini V10, and large V12 engines from BMW, Mercedes-Benz, and Rolls-Royce. The code will never appear on four-cylinder, inline-6, or V6 engines.

The most common root causes are electrical: a corroded or loose injector connector, a chafed or open wire in the cylinder 7 injector harness, or a failed injector solenoid coil. A low-circuit condition allows the lean mixture in cylinder 7 to generate detonation; the knock sensor detects it and the PCM retards ignition timing, causing the engine to run rough and lose power. Prompt diagnosis is important to prevent catalytic converter damage on petrol engines or potential injector-related engine damage on diesel applications.

Common causes

Most-frequently reported root causes when P0279 is logged.

  • 1
    Corroded, loose, or damaged electrical connector at the cylinder 7 injector.
  • 2
    Open circuit or excessive resistance in the injector control wiring between PCM and injector 7.
  • 3
    Failed injector solenoid coil (open winding) on cylinder 7.
  • 4
    Chafed harness contacting the intake manifold bracket, oil filter housing, or other sharp engine components.
  • 5
    Faulty Fuel Injector Control Module (FICM) on diesel platforms such as the 6.0/6.4 Power Stroke.
  • 6
    Short to ground on the injector low-side control wire.
  • 7
    PCM injector driver fault for cylinder 7 (uncommon; rule out harness and injector first).

Symptoms drivers notice

Malfunction Indicator Lamp (MIL) illuminated.
Rough idle and engine vibration from a dead or misfiring cylinder 7.
Noticeable power loss, especially under acceleration or load.
Reduced fuel economy.
Companion misfire code P0307 (cylinder 7 misfire) typically present.
Possible detonation or knock noise followed by ignition timing retard.

How to diagnose P0279

A typical diagnostic flow when this code is present.

  1. 1
    Connect a scan tool and retrieve all DTCs; note P0307 (misfire) or any FICM-related codes alongside P0279 to build a complete fault picture.
  2. 2
    Inspect the cylinder 7 injector harness routing — on V8 Power Stroke engines particularly check near the intake manifold bracket and oil filter area where chafing is common.
  3. 3
    Unplug the cylinder 7 injector connector and measure coil resistance with a DMM; compare to specification (typically 0.5–2.0 Ω for port injectors, lower for high-pressure CRDI or HEUI types).
  4. 4
    Use a noid light or injector pulse tester at the injector connector to confirm the PCM is delivering a drive signal while cranking.
  5. 5
    Back-probe the PCM injector driver pin for cylinder 7 to verify the control-side voltage swings to near 0 V when commanded; a stuck-high reading suggests a PCM driver fault.
  6. 6
    On Power Stroke diesel applications, test FICM output voltage (should be ~48 V); a weak or failed FICM is a common cause of injector circuit low codes across multiple cylinders.
  7. 7
    After repairing the confirmed fault, clear codes and verify the repair by monitoring live injector balance data or confirming P0279 and P0307 do not return after a full drive cycle.

Related powertrain codes

Frequently asked questions

Which engines can actually set P0279?

Only engines with seven or more cylinders: V8, V10, V12, and inline-8 configurations. Four-cylinder, V6, and inline-6 engines do not have a cylinder 7, so this code cannot appear on those platforms regardless of other faults present.

On a Ford Power Stroke, could the FICM cause P0279?

Yes. The 6.0 and 6.4 Power Stroke use a separate Fuel Injector Control Module that supplies approximately 48 V to fire the HEUI injectors. A failing FICM with degraded output voltage often sets injector circuit low codes on one or more cylinders, including cylinder 7. Test FICM output voltage before condemning individual injectors.

Is P0279 dangerous to ignore?

It should be addressed promptly. Cylinder 7 not firing means unburned fuel or air enters the exhaust, risking catalytic converter overheating on petrol engines. On diesel engines an injector stuck partially open risks hydro-lock and severe internal engine damage. Avoid sustained high-load driving until the fault is repaired.

Can I diagnose P0279 without specialist tools?

Basic diagnosis — inspecting the connector, measuring injector coil resistance, and checking for obvious harness damage — is within reach of a competent DIY mechanic with a DMM. However, confirming whether the PCM is generating a correct drive signal requires a noid light or oscilloscope, and reading FICM output voltage on diesel platforms needs a suitable scan tool or a lab-grade DMM.

Disabling P0279 in software

RaceTune can permanently disable P0279 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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