P0261 – Cylinder 1 Injector Circuit Low

P0261 is a fuel injector circuit trouble code that points to a problem with cylinder 1 on a gasoline or diesel engine. When this code sets, the engine computer (ECU/PCM) has detected that the injector for cylinder 1 is not seeing the correct voltage or current. That usually means an electrical issue, a faulty injector, or sometimes a wiring problem. If you ignore it, you can end up with poor fuel economy, misfires, and even engine damage over time. The good news is, with a methodical approach, P0261 is very fixable.

What Does P0261 Mean?

P0261 stands for “Cylinder 1 Injector Circuit Low.” In plain language, your ECU is commanding the injector on cylinder 1 to fire, but it sees lower than expected voltage or current in that circuit. The ECU constantly monitors injector feedback, and when the signal drops below a calibrated threshold, it stores P0261 and usually turns on the check engine light.

This is primarily an electrical code. It may be caused by a failing injector coil, corroded connector pins, damaged wiring, or in rarer cases, an internal fault in the ECU or a poor engine ground. It does not directly say the injector is clogged; it says the circuit is “low.”

Quick Reference

• Code: P0261 – Cylinder 1 Injector Circuit Low
• Type: Fuel injector electrical fault (cylinder 1)
• Common Symptoms: Rough idle, misfire, reduced power, poor fuel economy
• Risk Level: Moderate – usually drivable but can cause damage if ignored
• Typical Fixes: Repair wiring/connector, replace injector, occasionally ECU repair

Real-World Example / Field Notes

In the shop, I see P0261 most often on higher-mileage vehicles where the injector harness runs across the top of the engine. Heat and vibration slowly harden the insulation, and the wire to cylinder 1 starts to break internally near the connector. The car comes in with a rough idle and a flashing check engine light under load. A quick wiggle test on the harness with the engine running makes the misfire come and go. Repairing the broken section of wiring and cleaning the connector terminals fixes the issue without needing a new injector.

Symptoms of P0261

• Rough idle: Engine shakes or feels uneven, especially at stoplights.
• Misfire under load: Hesitation or stumbling when accelerating or climbing hills.
• Reduced power: Noticeable loss of performance and slower throttle response.
• Poor fuel economy: You burn more fuel as the ECU compensates for the misfire.
• Check engine light: Steady or flashing MIL, often with misfire codes like P0301.
• Fuel smell from exhaust: Unburned fuel if the injector is stuck open or firing erratically.
• Hard starting: Longer crank time, especially when hot, in more severe cases.

Common Causes of P0261

Most Common Causes

• Faulty injector on cylinder 1: The internal coil can short or partially short, pulling voltage low.
• Damaged injector wiring: Broken, chafed, or shorted wires between the injector and ECU.
• Corroded or loose connector: Green corrosion, bent pins, or a loose fit at the injector plug.
• Poor engine or chassis ground: Weak grounds cause low voltage in multiple circuits, including injectors.

Less Common Causes

• ECU/PCM internal fault: Failed injector driver circuit inside the control module.
• Aftermarket wiring mods: Remote starters, alarm systems, or performance harnesses spliced into injector wiring.
• Low system voltage: Weak alternator or battery causing borderline voltage, exposing a marginal injector circuit.
• Connector damage from prior repairs: Over-tightened loom clips or careless probe testing that weakened the terminals.

Diagnosis: Step-by-Step Guide

Before you start, you’ll want a basic scan tool, a digital multimeter, and ideally a noid light or test light designed for injectors. Access to a wiring diagram for your specific vehicle helps a lot. If you have an advanced scan tool with Mode $06 data and bi-directional controls, even better.

1. Confirm the code: Use a scan tool to read all stored and pending codes. Note if you also have misfire codes like P0301 or other injector codes (P0262–P0267). Clear the codes and see if P0261 returns quickly.
2. Visual inspection of injector 1: Locate cylinder 1 (check your service manual) and inspect the injector and connector. Look for broken locks, oil contamination, melted plastic, or obvious wire damage.
3. Wiggle test: With the engine idling, gently move the harness and connector for injector 1. If the engine stumbles or smooths out as you move it, you likely have an internal wire break or poor connection.
4. Check injector resistance: With the key off, unplug injector 1 and measure resistance across the two terminals using a multimeter. Compare to the spec and to another injector. A significantly lower resistance can cause a “circuit low” condition.
5. Verify power supply: Turn the key on (engine off) and check for battery voltage on the injector power wire using a multimeter or test light. Most systems supply 12 V to one side of all injectors and the ECU grounds the other side.
6. Check control/ground side: Use a noid light or scope on the control wire while cranking or running. You should see a pulsing signal. If the signal is weak or missing only at injector 1, trace that wire back to the ECU.
7. Inspect wiring continuity: With the connector unplugged at both the injector and ECU (if accessible), perform a continuity test on both wires. Also check for short-to-ground or short-to-power by measuring resistance to chassis ground and battery positive.
8. Swap test (if easy): On some engines, you can swap injector 1 with another cylinder. If the code follows the injector (for example, becomes P0264 cylinder 2), the injector itself is bad.
9. Check Mode $06 and misfire data: If your scanner supports it, look at Mode $06 misfire counters and injector data. High misfire counts on cylinder 1 support a true injector issue rather than a false code.
10. Evaluate ECU only after wiring and injector are proven good: If power, ground, wiring, and injector test fine, and the signal at the ECU pin is wrong, you may have a failed ECU driver circuit.

Pro tip: Never pierce injector wires with a test probe unless absolutely necessary. Use proper back-probing pins or breakout leads. Pierced insulation often becomes a future corrosion point and can bring this code right back.

Possible Fixes & Repair Costs

Repairs for P0261 range from very simple to moderately involved, depending on what you find during diagnosis. Parts prices vary by brand, engine type, and whether you use OEM or aftermarket components.

• Repair or replace wiring/connector: Splicing in new wire, replacing terminals, or installing a pigtail connector for injector 1. Typical shop cost: about $100–$250 depending on access and time.
• Replace injector on cylinder 1: New or remanufactured injector, plus labor. Typical range: $150–$400 per injector on most gasoline engines; some direct-injection or diesel injectors can be $400–$800 each.
• Clean and secure grounds: Cleaning ground points and tightening fasteners. Often bundled into diagnostic time, around $50–$150.
• ECU/PCM repair or replacement: Least common, but most expensive. Rebuilt or new ECU plus programming can run $500–$1,200+ depending on the vehicle.

Overall, you’re usually looking at a total repair cost in the $150–$600 range for typical wiring or injector issues. Factors that affect cost include engine layout (V6/V8 vs inline), injector accessibility under intake manifolds, whether multiple injectors are replaced as a set, and local labor rates.

Can I Still Drive With P0261?

In many cases, you can still drive with P0261, but it is not ideal. If the engine is only slightly rough and the check engine light is steady, short trips to get home or to a shop are usually fine. However, if the light is flashing, the misfire is severe, or the vehicle feels unsafe, you should avoid driving. A cylinder that is not fueling correctly can cause unburned fuel in the exhaust, overheating the catalytic converter and potentially damaging the engine over time.

What Happens If You Ignore P0261?

If you ignore P0261, a minor electrical issue can turn into bigger problems. Long-term misfires stress the catalytic converter, foul spark plugs, and can wash down cylinder walls with fuel, reducing lubrication. Fuel economy drops, drivability gets worse, and you may eventually face much higher repair bills than simply fixing the injector circuit when the code first appeared.

Last updated: January 22, 2026

Vehicles Commonly Affected by P0261

P0261 can show up on almost any modern fuel-injected engine, but it is especially common on certain platforms. Many Ford trucks and SUVs (F-150, Explorer, Expedition) and some GM vehicles (Silverado, Sierra, Tahoe, Suburban) see this code due to harness wear near the engine. It also appears on various Chrysler/Dodge/Jeep models, as well as some Volkswagen, Audi, and BMW engines where heat and vibration stress the injector wiring. High-mileage compact cars and small crossovers from brands like Toyota, Honda, Hyundai, and Kia can also develop this issue as the injector connectors age.