P0261
Cylinder 1 Injector Circuit LowP0261 is a generic OBD-II powertrain diagnostic trouble code: Cylinder 1 Injector Circuit Low. It is logged by the engine control unit when the fuel/inj monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0261 means
P0261 is stored when the ECM/PCM detects a lower-than-expected voltage in the fuel injector control circuit for cylinder 1. The ECM drives each injector by grounding its circuit through an internal transistor (injector driver); a low-circuit fault means the ECM is measuring a voltage that is too low — indicating an open coil winding, an open in the harness, or a short to ground that has collapsed the driver-side voltage.
Fuel injectors operate as solenoid valves: current through the coil pulls open a needle that admits high-pressure fuel into the combustion chamber. When the cylinder 1 injector circuit goes low, the injector either fails to open fully or does not open at all, causing cylinder 1 to receive little or no fuel. The result is a cylinder misfire, loss of power, and rough running that is typically worst at idle and low load.
The most common root causes are a corroded or loose injector connector, a broken wire in the injector harness, or a failed injector coil winding. The ECM driver IC itself rarely fails but should be tested last if the circuit checks out. Both gasoline and diesel engines are affected, and the code is often accompanied by a cylinder 1 misfire code (P0301).
Common causes
Most-frequently reported root causes when P0261 is logged.
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1
Open circuit in the cylinder 1 injector wiring harness (broken or corroded wire)
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2
Loose, corroded, or damaged electrical connector at the cylinder 1 fuel injector
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3
Shorted injector solenoid coil winding drawing excessive current and collapsing driver voltage
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4
High-resistance fault in the injector ground path
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5
Blown injector fuse or faulty injector relay cutting power to the circuit
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6
Failed ECM/PCM injector driver transistor for cylinder 1 (rare)
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7
Physically seized or stuck-open injector causing abnormal circuit loading
Symptoms drivers notice
How to diagnose P0261
A typical diagnostic flow when this code is present.
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1
Retrieve all DTCs and freeze-frame data with a scan tool; note whether P0301 or other cylinder-1 codes are also set.
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2
Visually inspect the cylinder 1 injector connector and wiring for corrosion, pushed-out pins, chafing, or heat damage.
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3
Disconnect the injector connector and measure injector coil resistance with a multimeter; typical specification is 12–16 Ω for port-injection solenoids (verify against manufacturer data).
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4
Perform a noid light test to confirm the ECM is generating a drive pulse to the injector connector.
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5
Check supply voltage at the injector connector with the ignition on; should be close to battery voltage on the power wire.
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6
Inspect the harness back to the ECM for pinched or broken wires; repair any damaged sections and retest.
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7
If the circuit and wiring test good but the fault persists, substitute a known-good injector to confirm injector failure before replacing.
Related powertrain codes
- P0065 — Air Assisted Injector Control Range/Performance
- P0066 — Air Assisted Injector Control Circuit or Circuit Low
- P0067 — Air Assisted Injector Control Circuit High
- P0087 — Fuel Rail/System Pressure - Too Low
- P0088 — Fuel Rail/System Pressure - Too High
- P0089 — Fuel Pressure Regulator 1 Performance
Frequently asked questions
Can a clogged injector cause P0261 even if the wiring is fine?
A clogged injector is more likely to cause a contribution/balance fault (P0263) than a circuit-low code. P0261 is specifically an electrical fault — the ECM has measured an abnormally low voltage in the driver circuit. A clogged but electrically healthy injector will not generate P0261 on its own.
Why does P0261 often appear together with P0301?
P0301 is a cylinder 1 misfire count code triggered by crankshaft speed irregularities. When the injector circuit is open (P0261), cylinder 1 receives no fuel, combustion does not occur, and the crankshaft deceleration is detected as a misfire. Both codes share the same root cause — the injector not firing.
Is the cylinder 1 injector always the faulty component when P0261 is set?
Not always. The code covers the entire circuit from the ECM driver pin to the injector coil. A broken wire or corroded connector anywhere in that circuit will produce the same code. Always trace the full circuit before condemning the injector itself.
What is the correct resistance range for a fuel injector coil?
It depends on injector type: port-injection solenoid injectors typically measure 12–17 Ω cold; high-impedance injectors used on many modern GDI engines measure 8–16 Ω; low-impedance peak-and-hold injectors (some diesel and older performance engines) measure 1–5 Ω. Always confirm against the manufacturer's service data for the specific application.
Disabling P0261 in software
RaceTune can permanently disable P0261 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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