OBD-II trouble code
P0279: Cylinder 7 Injector Circuit Low
A cylinder 7 code only appears on engines with at least eight cylinders, which changes both the likely vehicle and the likely cause — heat-hardened harness insulation at the back of the bank is disproportionately common here.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $50 – $1,600
- DIY difficulty
- Intermediate DIY
Browse every code in P0200–P0299, or start from the full code library.
What does P0279 mean?
The existence of this code tells you something about the engine before it tells you anything about the fault. A cylinder 7 requires at least eight cylinders, so P0279 belongs almost entirely to V8s — full-size trucks, large SUVs, body-on-frame vans and performance cars — with a small tail of V10 and V12 applications. Nothing with six cylinders or fewer can set it.
The fault itself is electrical. Injectors are supplied constantly and fired by the controller grounding the return side for a precisely timed pulse. A circuit-low complaint means that circuit is being held at ground outside the moments the controller is doing it deliberately. Either the injector winding has shorted internally or the drive wire is touching ground somewhere between the connector and the controller. Fuel pressure and delivery are not part of this picture.
Where this code differs practically from the same fault on a lower-numbered cylinder is position, and it is worth knowing before you start. On the common V8 layout that places odd cylinders on one bank, number 7 is the rearmost cylinder on its side. In a longitudinal engine bay that puts it hard against the bulkhead, at the end of the loom run, in the pocket of the bay with the least airflow and the most trapped heat. Two consequences follow.
The first is a failure mode. Wiring insulation ages with heat, and the injector harness at the back of a bank lives hotter than the same harness three cylinders forward. Insulation there goes hard, then cracks, then lets the conductor find a ground — which is exactly what this code detects. On cylinder 7 specifically, inspect the harness for stiff, brittle or split insulation before condemning the injector, because the population of faults at this position leans toward the wire in a way it does not at the front of the engine.
The second is money. The rearmost injector is frequently the one that cannot be reached without removing the intake manifold or working through the cowl, so a flat-rate quote based on an average injector may understate the labour considerably. Get the quote written for this cylinder rather than for the engine in general.
That point extends to the parts side. An eight-cylinder engine has eight injectors, so any suggestion to replace the set is an eight-part quote — and on a direct-injection V8 that is a very large number for what is currently evidence of one shorted circuit.
Common causes
- Heat-hardened, cracked harness insulation at the rear of the bank allowing the drive wire to ground
- Injector winding shorted internally
- Drive wire chafed against the manifold, the bulkhead or a bracket at the back of the engine
- Connector damaged or contaminated during previous intake manifold or valley work
- Terminals corroded or spread in a connector sitting under a heat-soaked area of the bay
- Failed injector driver in the controller, uncommon and only considered after the harness is cleared
Symptoms
- Check engine light on, frequently flashing under acceleration
- Pronounced misfire with one dead cylinder, worse under load than at idle
- Substantial power loss, noticeable on an eight-cylinder engine towing or loaded
- Rough idle and vibration through the body
- Fuel odour from the exhaust and rising consumption
- Companion misfire code for cylinder 7
Diagnostic steps
- 1.Confirm the engine has at least eight cylinders, then identify cylinder 7 from service data. On the common V8 layout it is the rearmost cylinder on the bank carrying the odd numbers.
- 2.Before anything else, inspect the injector harness at the rear of that bank for heat damage — insulation that has gone hard, discoloured, brittle or split. This position sees more thermal ageing than any other on the engine.
- 3.Unplug the cylinder 7 injector and clear the code. If it returns as an open circuit, the injector shorted internally; if the low complaint persists with nothing connected, the harness is grounded.
- 4.Measure winding resistance and compare against the other seven injectors rather than against specification alone. Seven matching readings and one low one is conclusive.
- 5.Check the connector for spread terminals and heat damage, which are more likely here than corrosion from water.
- 6.Trace the drive wire forward along its run, paying attention to where it passes the manifold and any bulkhead or bracket contact point.
- 7.Before authorising the repair, confirm what access this specific cylinder requires — a rear injector on a V8 often means intake removal, and that should be in the quote rather than a surprise.
Repair cost
$50 – $1,600
A heat-damaged section of harness repaired is typically $100 to $300. A single injector replaced runs about $200 to $600 port-injected, and $400 to $1,000 on a direct-injection V8 where the rail must come off. The wide top end reflects rear-cylinder access on a large engine — intake manifold removal alone can add two to four hours of labour, which is why a quote written for the average injector on this engine can be well short of the real figure.
Estimate your repair
Run the numbers for your vehicle
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.