OBD-II Code P0273 — What It Means & How to Fix It

What Does This Error Mean?

P0273 means the fuel injector circuit for Cylinder 5 is reading a low voltage or current signal. The ECM sends a signal to fire the Cylinder 5 injector and monitors the circuit response. When the return signal is lower than expected, the ECM logs P0273. This doesn't always mean the injector is physically broken — wiring faults, bad connectors, and ECM driver failures can all cause this code. Symptoms include rough idle, hesitation, and sometimes a Cylinder 5 misfire code at the same time.

Affected Models

All vehicles 1996+ with 5 or more cylinders
Common in V6, V8, and V10 engines
Common in vehicles with aging or rodent-damaged wiring harnesses
Common in high-mileage Ford, GM, and Chrysler trucks and SUVs

Common Causes

Corroded or loose connector at the Cylinder 5 fuel injector
Damaged wiring between the ECM and the Cylinder 5 injector with a break or short to ground
Faulty Cylinder 5 injector with an open circuit internally
Failed ECM driver circuit responsible for controlling the Cylinder 5 injector
Blown injector power supply fuse cutting voltage to the Cylinder 5 injector circuit

How to Fix It

Find the Cylinder 5 injector and unplug its electrical connector. Inspect both sides carefully for corrosion, bent pins, moisture, or loose locking tabs. Clean with electrical contact cleaner spray and reconnect securely.

On many V6 engines, the rear bank injectors (which often include Cylinder 5) are harder to access and go longer without inspection — corrosion is common.
Trace the injector wiring harness from Cylinder 5 back toward the ECM. Look for any spots where the wire has rubbed through, been pinched by a bracket, or been damaged by heat from nearby exhaust components.

Wiring damage near exhaust manifolds is extremely common on high-mileage vehicles.
Measure the resistance of the Cylinder 5 injector with a multimeter. Unplug the connector and probe the two injector terminals. A normal reading is 10–18 ohms on most port-injection vehicles. An open-circuit (infinite resistance) means the injector is internally broken.

Direct injection injectors may have different resistance specs — check your service manual for the correct value.
Check the fuel injector fuse and relay in your fuse panel. A blown fuse will kill all injectors in the affected circuit, but a partial fault in the fuse holder or relay can cause intermittent low-signal codes on individual cylinders.

Pull each fuse and visually inspect — a hairline crack in the fuse wire inside the casing isn't always visible without close inspection.
If wiring, connector, and injector all test normal, the problem may be in the ECM driver for Cylinder 5. Have a qualified shop use a breakout box to confirm ECM output before spending money on a new module.

Some specialty shops offer ECM driver circuit repair for a fraction of the cost of a replacement ECM.

When to Call a Professional

If you've verified the connector and wiring look good but P0273 returns, it's time for a professional circuit test. An ECM with a failed injector driver is an expensive repair — confirm this is the cause before committing to it. Also have a shop check if the injector is actually not firing — if Cylinder 5 is not getting fuel at all, you'll notice it as a strong misfire, not just a rough idle.

Frequently Asked Questions

Which cylinder is Cylinder 5 on my engine?

Cylinder numbering varies by manufacturer and engine layout. On most inline-5 engines, Cylinder 5 is the rearmost. On V6 and V8 engines, the numbering depends on the brand — check your vehicle's service manual or look up the cylinder layout for your specific engine online.

Will P0273 cause my car to fail an emissions test?

Yes, in most cases. An injector circuit fault will keep your OBD-II monitors from completing, or will result in an active fault code. Either way, the vehicle will fail an emissions inspection until the code is cleared and the monitors run successfully.

How much does it cost to fix P0273?

Connector cleaning or repair: Free to $50. Wiring harness repair: $100–$300. Injector replacement: $150–$400 installed. ECM repair or replacement: $300–$1,200+.