OBD-II Code P0280 — What It Means & How to Fix It

What Does This Error Mean?

P0280 means the fuel injector circuit for Cylinder 7 is reading a high voltage or current signal. When the ECM sees the Cylinder 7 circuit response is higher than normal, it stores P0280. This typically means there's a short to voltage somewhere in the circuit, or the injector itself has an internal short. A high-circuit fault can cause the injector to fire for too long or stay open continuously, over-fueling the cylinder. Symptoms include a strong raw fuel smell, rough running, and sometimes heavy black exhaust smoke.

Affected Models

All vehicles 1996+ with 7 or more cylinders
Common in V8, V10, and V12 engines
Common in vehicles with aging or heat-damaged rear-bank injector wiring
More frequent after improperly performed injector harness repairs

Common Causes

Short to voltage in the Cylinder 7 injector control wiring
Internally shorted Cylinder 7 injector drawing abnormally high current
Damaged wiring harness where the Cylinder 7 control wire contacts a 12V source
Wrong-spec injector installed with a lower resistance rating than the circuit requires
ECM internal driver fault for Cylinder 7 stuck in a high-output state

How to Fix It

Trace the Cylinder 7 injector wiring harness and look for any signs of bare wire, melted insulation, or a wire lying against a power-carrying component. On V8 and V10 trucks, the rear cylinders' wiring often runs near the firewall and battery area.

A brief visual of the harness takes minutes and can immediately reveal an obvious short to power.
With the Cylinder 7 injector unplugged and the key in the ON position, measure voltage on the control wire terminal in the harness connector. It should read near zero when the ECM is not commanding the injector. A 12V reading confirms a short to power in that wire.

The power-supply terminal will always read 12V — that's normal. It's the control terminal you're checking for an unexpected high voltage.
Test the Cylinder 7 injector resistance directly. Probe its two terminals with a multimeter set to ohms. A reading well below the normal 10–18 ohm spec — especially very close to zero — indicates an internal short. That injector must be replaced.

A zero-ohm or near-zero injector will conduct maximum current at all times and can damage the ECM driver circuit if left installed.
If recent injector work was done, verify the replacement injector's part number and resistance specification. Installing a performance or diesel injector with a low-impedance winding in a high-impedance circuit will trigger a high-circuit code every time the engine runs.

OEM injectors are the safest choice unless the vehicle has been professionally tuned for aftermarket injectors.
If wiring and injector both check out, request professional ECM testing with a lab scope. The ECM driver for Cylinder 7 may be stuck on or producing an out-of-spec signal. Confirm ECM failure with objective test data before purchasing a replacement.

A faulty ECM driver can sometimes be repaired by an ECM specialist at a lower cost than full replacement.

When to Call a Professional

If the Cylinder 7 injector is running continuously due to a high circuit condition, your engine is being over-fueled significantly. Over-fueling washes cylinder walls, ruins oxygen sensors rapidly, and can destroy a catalytic converter in short order. If you detect a persistent raw fuel smell or see black smoke at idle, stop driving and seek professional diagnosis immediately.

Frequently Asked Questions

What is the difference between P0279 and P0280?

Both involve Cylinder 7's injector circuit. P0279 is a LOW circuit reading — usually a broken wire, bad connector, or open injector. P0280 is a HIGH circuit reading — usually a short to voltage, shorted injector, or wrong-spec injector. They require different diagnostic approaches even though they affect the same cylinder.

Can a P0280 fault damage the ECM?

Yes, potentially. A shorted injector with near-zero resistance draws far more current than the ECM driver was designed to handle. Extended operation with a shorted injector installed can overheat and destroy the ECM's driver circuit. If you find a shorted injector, replace it promptly and have the ECM driver verified to be undamaged.

How much does it cost to fix P0280?

Wiring repair: $100–$300. Injector replacement: $150–$400 installed. ECM repair or replacement: $300–$1,200+.