P0272 – Cylinder 4 Contribution/Balance

P0272 is an OBD-II trouble code that points to a problem with one specific cylinder in your engine: “Cylinder 4 Injector Circuit Low.” In plain terms, your engine computer sees an electrical issue in the fuel injector circuit for cylinder #4, usually low voltage or high resistance. That can lead to rough running, misfires, and possible engine damage if you ignore it. In this guide, you’ll learn what P0272 means, common causes, symptoms, how a mechanic diagnoses it, possible repairs, and whether it’s safe to keep driving.

What Does P0272 Mean?

P0272 is a generic powertrain code that indicates the ECU (engine control unit) has detected an electrical fault in the fuel injector circuit for cylinder 4. “Circuit low” means the voltage or current returning from that injector is lower than the ECU expects, usually due to wiring, connector, or injector problems.

When this happens, the injector may not deliver the correct amount of fuel to cylinder 4. The result is poor combustion in that cylinder, which can cause misfires, loss of power, and increased emissions. On many vehicles, the ECU will also disable that injector to protect the engine and catalytic converter.

Quick Reference

• Code: P0272 – Cylinder 4 Injector Circuit Low
• System: Fuel injection / engine management
• Severity: Moderate to serious (can damage engine/catalyst if ignored)
• Common causes: Bad injector, wiring fault, poor connector, ECU driver fault
• Typical symptoms: Misfire, rough idle, loss of power, poor fuel economy

Real-World Example / Field Notes

In the shop, I see P0272 most often on higher-mileage trucks and SUVs that tow or work hard. A typical case: a diesel pickup comes in with a rough idle, heavy fuel smell, and the MIL (check engine light) on. Scan shows P0272 plus a cylinder 4 misfire code. A quick wiggle test on the injector harness makes the engine stumble even more. Pulling the connector reveals green corrosion and a broken wire inside the insulation. After repairing the harness and cleaning the connector, the misfire disappears and P0272 never returns.

Symptoms of P0272

• Check engine light on: The MIL will usually illuminate and store P0272, sometimes with misfire codes.
• Rough idle: Cylinder 4 not fueling correctly causes a shaky or uneven idle.
• Loss of power: You may feel sluggish acceleration, especially under load or climbing hills.
• Engine misfire: Noticeable stumble, hesitation, or vibration when you accelerate or cruise.
• Poor fuel economy: The ECU may overcompensate with extra fuel, or the engine runs inefficiently.
• Fuel smell or smoke: On some engines (especially diesels), you may see excess exhaust smoke or smell raw fuel.
• Hard starting: In more severe cases, the engine may crank longer or struggle to start.

Common Causes of P0272

Most Common Causes

• Faulty fuel injector (cylinder 4): Internal coil failure, shorted windings, or high resistance in the injector itself can cause a low circuit signal.
• Damaged injector wiring: Chafed, pinched, or broken wires between the injector and ECU are very common, especially near the valve cover or harness clips.
• Corroded or loose connector: Moisture, oil, or dirt in the injector connector can increase resistance and drop voltage.
• Poor ground or power supply: Shared power or ground circuits for the injectors can cause one cylinder to act up first, often showing as P0272.

Less Common Causes

• ECU driver failure: The internal transistor (driver) that controls injector 4 inside the ECU can fail, causing a low circuit condition.
• Aftermarket tuner or wiring mods: Poorly installed performance chips, tuners, or remote-start systems can interfere with injector circuits.
• Rodent damage: Chewed wiring under the hood can partially break the injector circuit.
• Connector pin fit issues: Spread or loose terminals that don’t clamp tightly on the injector pins can create intermittent low signal.
• Internal engine problems: Rarely, severe mechanical issues in cylinder 4 (like a dropped valve seat) can cause misfire and confuse diagnosis, though they don’t directly cause the “circuit low” reading.

Diagnosis: Step-by-Step Guide

To diagnose P0272 correctly, you’ll want at least a basic scan tool, a digital multimeter, and ideally a noid light or an oscilloscope. Access to wiring diagrams and service information for your specific vehicle is also very helpful. If you’re not comfortable working around fuel and electrical systems, this is a good job to leave to a professional.

1. Confirm the code and check for companions. Use a scan tool to read all stored and pending codes. Note any misfire codes (like P0304) or other injector-related codes. Clear the codes and see which ones return.
2. Inspect injector 4 and harness visually. Locate cylinder 4 (check your service manual for the firing order). Inspect the injector, connector, and nearby wiring for rubbing, oil saturation, burns, or obvious damage.
3. Perform a wiggle test. With the engine idling, gently move the injector 4 harness and connector. If the engine stumbles or the code sets quickly, you likely have a wiring or connector issue.
4. Check injector resistance. With the key off, unplug injector 4 and measure resistance across its terminals with a multimeter. Compare to the spec and to another injector. A reading that’s significantly higher, lower, or open indicates a bad injector.
5. Verify power and ground at the injector. With the key on, use a multimeter or test light to confirm you have proper voltage on the injector power feed and a good ground or ECU-controlled side (depending on design).
6. Use a noid light or scope. Plug a noid light into the injector connector or back-probe with an oscilloscope to see if the ECU is pulsing the injector correctly. A weak or missing pulse can indicate an ECU or wiring issue.
7. Check continuity to the ECU. If power and ground look good but the circuit reads low, use an ohmmeter to check for continuity and resistance between the injector connector and ECU pins. Look for high resistance or opens.
8. Swap injectors (if accessible). On many engines, you can swap injector 4 with another cylinder. If the code moves to the other cylinder (e.g., becomes P0275 for cylinder 5), the injector itself is bad.
9. Inspect for shared circuit problems. If multiple injector codes are present, check common grounds, fuses, and relays that feed the injector bank.
10. Evaluate the ECU last. Only after wiring and injector tests pass should you suspect a faulty ECU driver. In some cases, Mode $06 data can help confirm repeated injector 4 misfire events.

Pro tip: Always disconnect the battery or pull the fuel pump fuse when unplugging multiple injectors or working around exposed fuel rails to reduce fire risk and prevent accidental short circuits.

Possible Fixes & Repair Costs

Repairs for P0272 depend on what’s actually wrong. Common fixes include replacing the cylinder 4 injector, repairing or replacing damaged wiring, cleaning or replacing the injector connector, or in rare cases replacing the ECU. Typical costs vary by vehicle and engine type, but you can expect around $150–$400 for a single injector replacement on many gas engines, $300–$800 or more on some diesels, $100–$300 for wiring/connector repairs, and $600–$1,200+ if an ECU replacement and programming is required. Labor rates, parts quality, and engine accessibility all affect the final bill.

Can I Still Drive With P0272?

You can usually drive a short distance with P0272, but it’s not a good idea to ignore it. If cylinder 4 is not fueling correctly, the engine may run lean or rich on that cylinder, causing roughness and potential damage. Unburned fuel can overheat and ruin the catalytic converter, while lean combustion can raise cylinder temperatures. If the engine is shaking badly, misfiring under load, or flashing the check engine light, you should avoid driving and have it towed to a shop.

What Happens If You Ignore P0272?

Ignoring P0272 for too long can turn a relatively simple injector or wiring repair into a bigger problem. Persistent misfires can damage the catalytic converter, foul spark plugs, contaminate engine oil with fuel, and in extreme cases cause piston or valve damage from abnormal combustion. You’ll also waste fuel and risk being stranded when the injector or wiring finally fails completely.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0272

P0272 shows up on a wide range of OBD-II vehicles, but it’s especially common on trucks and SUVs with multi-port or common-rail injection. You’ll often see it on Ford Power Stroke diesels, GM Duramax trucks, Ram Cummins diesels, and gasoline engines from Ford, Chevrolet, Dodge, Toyota, and Nissan. High-mileage work trucks, vans, and fleet vehicles that see heavy loads or lots of idling tend to develop injector and harness issues more frequently, which is when P0272 appears.