OBD-II trouble code
P0279: Cylinder 7 Injector Circuit Low
The cylinder 7 injector control circuit read low — usually a wire shorted to ground or a shorted injector coil. Cylinder 7 only exists on eight-cylinder and larger engines, and its position depends entirely on how your manufacturer numbers the banks.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $50 – $1,500
- DIY difficulty
- Intermediate DIY
What does P0279 mean?
The engine control module (ECM) switches each fuel injector on the ground side. Switched battery voltage sits on one injector terminal, and the ECM fires the injector by pulling the other terminal to ground for a metered pulse width. Between pulses that control wire should sit near battery voltage, because nothing should be tying it to ground.
P0279 sets when the ECM sees the cylinder 7 control circuit reading low while it expects high — the circuit is grounded when it should be floating. The usual causes are a control wire chafed through and touching the block, head, or a bracket, an injector with a shorted coil winding, or corrosion and moisture bridging pins inside the connector. Some platforms also set the code when current through the circuit falls below the expected range.
Cylinder 7 exists only on V8, inline-eight, V10 and V12 engines, and finding it is where most of the wasted time on this code happens. Two conventions dominate and they place cylinder 7 in completely different spots. On most General Motors small-block and LS-family V8s, the driver's-side bank is numbered 1-3-5-7 front to back, so cylinder 7 is the rearmost cylinder on the driver's side. On Ford modular V8s, the driver's-side bank is 5-6-7-8 front to back, so cylinder 7 is the third cylinder back on that side. Chrysler and Hemi V8s use their own arrangement again, and imported V8s vary further. It is also worth being clear that cylinder numbering is not the firing order — the firing order tells you when a cylinder fires, not where it sits. Look up the numbering diagram for your specific engine and physically identify the cylinder before a connector comes apart.
Wherever cylinder 7 lands, on a V8 it is a rearward cylinder on one bank, which means its harness runs through the hottest and least accessible part of the engine bay, near exhaust manifolds and often under a brake booster, wiper cowl, or heater box. Heat-hardened insulation, chafe against a manifold stud, and corrosion from cowl runoff are all more common there than at the front of the engine, so the harness deserves suspicion before the injector does.
With the circuit low, cylinder 7 is not being fueled as the ECM intends, so a misfire is likely and P0307 often appears alongside. Unburned fuel entering the exhaust can superheat the catalytic converter on that bank, and on a V8 with two converters the damage lands on the one serving cylinder 7's side.
Common causes
- Cylinder 7 injector control wire chafed through and shorted to ground
- Shorted coil winding inside the cylinder 7 injector
- Corrosion or water intrusion in the injector connector, common on rearward cylinders near the cowl
- Heat-hardened or melted harness insulation near the exhaust manifold on that bank
- Wire pinched or trapped during a prior intake manifold, valve cover, or exhaust manifold repair
- Damaged, spread, or backed-out terminal in the injector connector
- Rodent damage to the injector harness where it runs along the back of the engine
- Rarely, a failed cylinder 7 injector driver circuit inside the ECM/PCM
Symptoms
- Check engine light on, sometimes flashing under load
- Rough idle with a noticeable engine shake
- Misfire on cylinder 7, commonly with a companion P0307
- Loss of power and hesitation under acceleration
- Raw fuel smell from the exhaust
- Increased fuel consumption
- Hard starting or extended cranking in some cases
Diagnostic steps
- 1.Confirm P0279 and record all companion codes. A cylinder 7 misfire (P0307), the paired high code P0280, or codes on neighboring cylinders each shift the emphasis.
- 2.Look up the cylinder numbering diagram for your exact engine and physically locate cylinder 7. On GM V8s it is the rearmost cylinder on the driver's bank; on Ford modular V8s it is third back on the driver's bank. Do not infer the location from the firing order.
- 3.Inspect the cylinder 7 injector connector and the harness that reaches it for corrosion, melted or hardened insulation, and backed-out terminals. Follow the loom where it passes near exhaust heat.
- 4.With the key off, unplug the injector and measure its coil resistance. Compare it to specification and to the other injectors — a reading well below spec confirms a shorted coil.
- 5.Disconnect both the injector and the ECM connector, then check the control wire for continuity to ground. Any continuity confirms a short in the harness rather than a bad injector.
- 6.Wiggle-test the harness along the rear of that bank, focusing on manifold studs, bracket edges, and any point where the loom has worn thin.
- 7.With the wiring and injector verified good, use a noid light or the scan tool injector test to confirm the ECM is pulsing the circuit normally.
- 8.If everything external tests correct and the drive signal is still wrong, suspect the ECM injector driver — verify with the manufacturer's pinout test before condemning the module.
Repair cost
$50 – $1,500
Repairing a chafed wire or a corroded connector is often $75-$250. A single fuel injector is $60-$400 in parts plus 0.5-3 hours of labor; on most V8s cylinder 7's injector is reachable from the top once the fuel rail cover or plenum is off, but access at the rear of the bank is tight and shops usually quote toward the upper end. Diesel V8 injectors commonly run $400-$900 each installed. A failed ECM injector driver is uncommon and runs $500-$1,500 including programming. Diagnosis alone is typically $75-$150.
Estimate your repair
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Open the Repair Cost Estimator with fuel injector replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.