P0273 – Cylinder 5 Injector Circuit Low

P0273 is a diagnostic trouble code that points to a problem with cylinder #5 fuel injector control, usually an electrical or circuit issue. When this code sets, your engine computer (ECU) has detected that the injector for cylinder 5 isn’t operating within the expected range. You might notice rough running, loss of power, or a flashing check engine light, especially under load. Left alone, it can lead to misfires and even internal engine damage. In this guide, you’ll learn what P0273 means, common causes, symptoms, and how you or a shop can fix it.

What Does P0273 Mean?

P0273 is defined as “Cylinder 5 Injector Circuit Low.” In plain language, the ECU is seeing lower than expected voltage or signal on the control circuit for the fuel injector on cylinder #5. That can be caused by wiring issues, a failing injector, or sometimes a problem inside the engine computer itself.

Most systems use the ECU to ground the injector to fire it. If the ECU sees the circuit is “pulled low” all the time, or the current flow doesn’t match what it expects, it flags P0273. This is an electrical code, not a mechanical one, but it can quickly lead to mechanical damage if the cylinder runs lean or doesn’t fire correctly.

Quick Reference

• Code: P0273
• Definition: Cylinder 5 Injector Circuit Low
• System: Fuel injection / engine controls
• Severity: Moderate to severe (risk of engine damage if ignored)
• Typical cause: Faulty injector, wiring fault, or poor connection at cylinder #5

Real-World Example / Field Notes

In the shop, I see P0273 most often on higher-mileage trucks and SUVs that tow or see heavy use. One recent case was a 5.4L V8 pickup with rough idle and poor towing power. Scan data showed misfires on cylinder 5 and P0273 stored. A quick wiggle test on the injector harness made the engine stumble worse. Pulling back the loom revealed a partially broken wire rubbing on the valve cover. After repairing the wire and clearing the code, fuel trims normalized and the truck ran smoothly again. The injector itself was fine; the wiring was the real culprit.

Symptoms of P0273

• Check engine light on: Often steady at first, may flash under load if misfires are severe.
• Rough idle: Engine may shake or feel uneven, especially when stopped in gear.
• Loss of power: Noticeable lack of acceleration, especially when climbing hills or towing.
• Poor fuel economy: Extra fuel may be dumped into other cylinders to compensate, wasting gas or diesel.
• Engine misfire: Hesitation, stumbles, or a “chugging” feel, often most noticeable at low RPM.
• Hard starting: Longer crank times or needing to press the throttle to get it to fire.
• Fuel or exhaust odor: Raw fuel smell from the tailpipe if the cylinder isn’t burning properly.
• Possible limp mode: Some vehicles reduce power to protect the engine and emissions system.

Common Causes of P0273

Most Common Causes

• Faulty cylinder 5 injector: Internal short, coil failure, or stuck injector can cause low circuit voltage.
• Damaged injector wiring: Chafed, pinched, or broken wires between the injector and ECU are very common.
• Corroded or loose connector: Poor contact at the injector plug or intermediate connectors creates high resistance and low signal.
• Poor ground or power feed: On some designs, shared power or ground issues affect only certain cylinders.
• Previous engine work: Harness not clipped back correctly after repairs, leading to rubbing and wire damage.

Less Common Causes

• ECU (PCM) internal fault: Failed injector driver for cylinder 5 can set P0273, though this is less frequent than wiring or injector issues.
• Water intrusion: Moisture in the harness or connectors, especially in trucks and off-road vehicles.
• Aftermarket modifications: Poorly installed performance tuners, remote starters, or piggyback systems spliced into injector wiring.
• Rodent damage: Chewed wires near the intake manifold or along the injector harness.
• Incorrect injector type: Wrong resistance or flow-rate injector installed on cylinder 5 after previous repairs.

Diagnosis: Step-by-Step Guide

To diagnose P0273 properly, you’ll want a quality scan tool, a digital multimeter, and ideally an injector test light or noid light. Access to wiring diagrams and service information for your specific vehicle is also very helpful. If you’re comfortable with basic electrical testing, you can do several of these checks yourself before heading to a shop.

1. Confirm the code and freeze-frame data: Use a scan tool to read P0273 and note engine load, RPM, and temperature when it set. Check for related misfire or injector codes.
2. Inspect cylinder 5 location: Identify which cylinder is #5 for your engine layout (this varies by make). Verify you’re working on the correct injector.
3. Visual inspection of injector and harness: Look for broken clips, melted insulation, rubbing points, or oil-soaked connectors on the cylinder 5 injector wiring.
4. Wiggle test: With the engine idling, gently move the harness and connector for injector 5. If the idle changes or stumbles, you likely have an intermittent wiring or connector issue.
5. Check injector resistance: Key off, unplug the injector, and use a multimeter to measure resistance across the injector terminals. Compare to spec and to other injectors. A reading far off from the others indicates a bad injector.
6. Verify power and ground: With key on, use a test light or multimeter to confirm proper voltage at the injector connector and that the ECU control side can switch the ground on and off.
7. Use a noid light or scope: Plug a noid light into the injector connector or use an oscilloscope to observe the injector pulse. A weak or missing pulse on cylinder 5, with good wiring, points toward an ECU driver issue.
8. Swap-test components (if accessible): On some engines, you can swap injector 5 with another cylinder. If the code or misfire follows the injector, the injector is at fault. If it stays on cylinder 5, suspect wiring or ECU.
9. Check Mode $06 data: Some scan tools allow you to view misfire and injector performance counts per cylinder. High counts on cylinder 5 support an injector or circuit problem there.
10. Inspect for related damage: If the injector has been shorted for a while, check for signs of overheated wiring, melted connectors, or other collateral damage.

Pro tip: Always load-test circuits. A wire can show good voltage with a meter but fail under load. Using a test light or a headlamp bulb as a load can reveal weak connections that a simple voltage check misses.

Possible Fixes & Repair Costs

Repairs for P0273 depend on what you find during diagnosis. Common fixes include replacing the cylinder 5 injector, repairing or replacing damaged wiring, cleaning and tightening connectors, or in rare cases replacing the ECU. Parts and labor costs vary widely by vehicle type and engine design.

• Replace cylinder 5 injector: $150–$500 parts and labor, depending on access and whether it’s gas or diesel.
• Repair injector wiring/connector: $100–$350, more if a large section of harness must be replaced.
• ECU (PCM) replacement and programming: $600–$1,500+ including programming, usually a last-resort fix.
• Additional work (plugs, coils, cleaning): Often done at the same time, adding $100–$400.

Factors that affect cost include engine layout (V6/V8 vs. inline), whether the intake manifold must be removed, OEM vs. aftermarket injectors, and local labor rates. A thorough diagnosis up front saves money by avoiding unnecessary parts replacement.

Can I Still Drive With P0273?

You can sometimes drive short distances with P0273, but it’s not recommended. If the injector for cylinder 5 isn’t working correctly, that cylinder may run lean, misfire, or not fire at all. This can overheat the catalytic converter, wash down cylinder walls with fuel, and cause internal engine wear. If the check engine light is flashing or the engine runs very rough, you should avoid driving and have the vehicle towed to prevent further damage.

What Happens If You Ignore P0273?

Ignoring P0273 can turn a relatively simple electrical or injector repair into a much bigger problem. Continuous misfires can damage the catalytic converter, foul spark plugs, contaminate engine oil with fuel, and in extreme cases lead to piston or valve damage. Fuel economy and performance will suffer, and you may eventually end up with a no-start condition or multiple related trouble codes.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0273

P0273 shows up most frequently on multi-cylinder engines where injector harnesses run along the intake or valve covers. You’ll often see it on Ford, GM (Chevrolet, GMC, Cadillac), and Chrysler/Dodge/Ram trucks and SUVs with V6 and V8 engines, as well as some Jeep models. It also appears on certain European and Japanese vehicles with direct injection systems, including some BMW, Mercedes-Benz, Nissan, and Toyota engines. High-mileage work trucks, diesel pickups, and vehicles used for towing or off-road driving are especially prone due to heat, vibration, and harness wear.