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OBD-II Diagnostic Trouble Code

P0261 — Cylinder 1 Injector Circuit Low

P0261 means the ECM detected a low voltage or low current condition in the cylinder 1 injector control circuit. This typically indicates a short to ground on the injector circuit or a shorted injector coil, as seen by the injector driver. The ECM usually disables or limits that injector once the fault is confirmed.

Severity 4/5 Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi Cylinder 1 Injector Circuit Low
Code
P0261
Category
Powertrain
Subsystem
Fuel
Truck-relevant
Yes
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What this means for truckers

P0261 (Cylinder 1 Injector Circuit Low) on a commercial diesel — the ECM detected lower than expected current draw from the cylinder 1 injector. Causes: damaged injector wiring, corroded connector at the injector, or a failed injector solenoid. Test resistance of the injector coil against factory spec (typically 0.5-3 ohms depending on engine). Common-rail diesel injectors run $400-1,200 each on Cummins/Detroit. Diagnose with cylinder balance test first — if cylinder 1 contribution is low but injector resistance is good, the wiring is the issue.

Before you replace parts — try this first

P0261 on the Fuel system is most often injector harness shorted to ground (chafed wire, damaged under-valve-cover harness on diesels) — not a dead part. On commercial diesels especially, work these in order before spending money on parts:

  1. Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
  2. Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
  3. Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
  4. Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
  5. Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms

Cylinder 1 may go dead, causing a noticeable miss, rough idle, vibration, low power and possible white or gray smoke on a diesel. A related misfire or cylinder balance code is common, and some engines derate or disable the injector bank sharing the same driver.

Common causes
  • CommonInjector harness shorted to ground (chafed wire, damaged under-valve-cover harness on diesels) ($150–$800)
  • CommonShorted cylinder 1 injector solenoid coil ($400–$2500)
  • OccasionalContaminated or oil-soaked injector connector causing leakage to ground ($100–$400)
  • RareECM injector driver failure ($1200–$3500)
How to fix
Measure cylinder 1 injector coil resistance at the ECM connector and at the injector, and check each lead for continuity to ground.
When to use: First step to separate harness faults from injector faults.
Inspect and repair the injector harness, including any internal harness under the valve cover on diesels.
When to use: When the short to ground is in the harness.
Swap the injector connector or injector to another cylinder (where practical) to see if the fault follows.
When to use: When the coil reading is borderline.
Replace the cylinder 1 injector and perform any required injector trim/calibration code programming.
When to use: When the injector coil is confirmed shorted.
Affects most

No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.

Related

Frequently Asked Questions

Can I drive with code P0261?
Drive with caution. P0261 is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix P0261 on a commercial truck?
Total repair cost ranges $100–$3500 depending on the root cause. The cheapest fix is usually the first one listed below — Injector harness shorted to ground (chafed wire, damaged under-valve-cover harness on diesels) — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0261 fail a DOT inspection?
P0261 itself doesn't automatically fail an inspection, but if the truck is in reduced-power mode (limp mode) at the time of inspection, it WILL be flagged. Most inspectors will note the check engine light but pass the truck if it's running and performance is normal. Fix it before a Level 1 inspection regardless.
What's the difference between P0261 and related codes?
P0261 is closely related to: P0200 (Injector Circuit Malfunction), P0201 (Injector Circuit Malfunction - Cylinder 1), P0202 (Injector Circuit Malfunction - Cylinder 2), P0203 (Injector Circuit Malfunction - Cylinder 3). These codes share the same subsystem (fuel) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0261 is set without the companions, the issue is more isolated.
How do I prevent P0261 from coming back after a repair?
For P0261 (Cylinder 1 Injector Circuit Low), prevention centers on the fuel system. Replace fuel filters at the OEM interval — don't stretch them. Use only diesel from high-volume fuel stops (avoid bottom-of-tank fuel at low-traffic stations). Add a water separator if you don't have one. After repair, prime the fuel system per the engine manual.

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