P0261
- Powertrain
- Generic (SAE)
- Emissions
Get it looked at now
A cylinder that is not fueled correctly produces misfire, which pushes raw oxygen and potentially raw fuel through the catalytic converter. A control circuit shorted to ground can hold the injector open whenever the circuit is powered, so fuel can enter the cylinder at rail pressure with the engine stopped — that washes oil off the cylinder wall, dilutes the engine oil, and in the worst case leaves enough liquid fuel in the cylinder to hydrolock it on the next crank. The short can also destroy the module's injector driver, turning a wiring repair into an ECM job.
- Safe to drive
- Drive only far enough to get it repaired, and stop and tow if the light flashes — the catalytic converter is being damaged. If the engine cranks unusually hard, smells strongly of raw fuel, blows heavy exhaust smoke, or the oil level is rising, do not crank or drive it: a stuck-open injector can fill the cylinder with fuel and hydrolock the engine.
Cylinder 1 Injector Circuit Low
The computer's control circuit for the cylinder 1 fuel injector is reading low when it should read high — usually a wire shorted to ground or an injector shorted internally. That cylinder is very likely not being fueled correctly.
Port fuel injectors are typically fed battery voltage on one side while the engine control module switches the other side to ground through an internal driver. The module monitors the voltage on that control pin. P0261 sets when the pin sits low outside the commanded pulse, or when current draw exceeds what the driver allows — the classic causes being the control wire shorted to ground, an injector winding shorted internally, or a failed driver. Note that a completely open injector winding usually sets the corresponding open or high circuit code rather than this one, though some manufacturers combine open and low criteria. Direct-injection engines drive injectors from a high-voltage boost circuit, and their fault criteria and testing procedures are different and more hazardous.
How the car detected itThe module compares the voltage at its injector control pin against expected levels for the driver's on and off states, and may also monitor current through the driver. A pin held low when the driver should be off, or current above the driver's limit, sets the fault — usually fast, often within seconds of key-on or the first crank. Many modules disable that driver to protect themselves once the fault is detected, which is why the cylinder goes completely dead. Thresholds and disable strategies vary.
A trouble code records what a control module measured. It does not identify which part failed. Test before replacing anything.
- Safe to drive
- Drive only far enough to get it repaired, and stop and tow if the light flashes — the catalytic converter is being damaged. If the engine cranks unusually hard, smells strongly of raw fuel, blows heavy exhaust smoke, or the oil level is rising, do not crank or drive it: a stuck-open injector can fill the cylinder with fuel and hydrolock the engine.
- Urgency
- Get it looked at now
- Will it pass emissions
- No
- If ignored
- Expect fuel dilution of the oil, cylinder bore washdown, and accelerated wear on that cylinder. Sustained misfire overheats and melts the catalytic converter substrate. An injector held open by a shorted control circuit can fill the cylinder with liquid fuel while the engine sits, and cranking against that can bend a connecting rod — a far larger repair than the wiring fault that caused it. If the short kills the module's injector driver, engine control module repair or replacement joins the bill, along with the programming that goes with it.
- Check engine light
- Solid
- Clearing the light
- A completed drive cycle is normally required before the monitor re-runs and the light can clear.
These are the causes this code can have. For the order to work through them in, see what to check first.
| # | Cause | How often | Component |
|---|---|---|---|
| 1 | Injector winding failed open | Very common | — |
| 2 | Wiring or connector fault | Common | — |
| 3 | Connector pins corroded - high contact resistance | Occasional | — |
Ordering reflects how often each cause is responsible in general, not a probability for your vehicle. Confirm by testing.
In order. Each of these is cheaper or faster than what follows it, and each one can make the rest unnecessary.
Whether a misfire code for the same cylinder is also stored
P0261 plus a cylinder 1 misfire code tells you the electrical fault is actually killing combustion. P0261 with no misfire suggests an intermittent circuit fault that has not yet fully disabled the injector.
Which cylinder is number 1 on this specific engine
Cylinder numbering varies by manufacturer and is not always the one nearest the front of the vehicle or the accessory belt. Confirm against service information before removing anything.
The injector connector and the harness run above it
The injector harness lies on top of a hot engine, close to brackets, the fuel rail, and the intake. Chafe-through to a grounded surface is the classic cause of a low circuit code, and it is often visible once you lift the loom.
Any recent work involving the intake manifold, fuel rail, or engine harness
A wire pinched during reassembly is far more probable than an injector that failed spontaneously, and it is quick to rule in or out.
Engine oil level and smell, and whether the engine cranks normally
An injector that has been dumping fuel raises oil level and leaves a fuel smell on the dipstick. A hard, unusually slow crank alongside that is a hydrolock warning — stop cranking and pull the plug on that cylinder before going further.
Confirm the code is current and capture freeze frame before clearing
Tools Scan tool with freeze frame and live data
Note whether it sets at key-on, at crank, or only under load, and what other codes accompany it. Record misfire counters for that cylinder if available.
ExpectedA current code that reappears immediately on key cycle points at a hard short. One that only sets under vibration or heat points at chafe or a connector.
Measure injector winding resistance at the injector, disconnected and cold
Tools Digital multimeter
Test the suspect injector and then every other injector on the engine under the same conditions. Comparison across cylinders is far more useful than any generic number.
ExpectedA value in line with its siblings. Port injectors run from a few ohms (low-impedance) to roughly the mid-teens in ohms (high-impedance) depending on the system — the correct figure is engine-specific. A reading clearly below its neighbors indicates a shorted winding.
Verify supply voltage on the injector's feed side
Tools Digital multimeter with backprobes, wiring diagram
Backprobe the feed pin with the key on. Confirm the feed is present and that it matches the other injectors.
ExpectedBattery voltage on the feed pin on most port-injection systems. Some systems energize injector power only through a relay under specific conditions, so check the wiring description for the vehicle rather than assuming.
Test the control wire for a short to ground
Tools Digital multimeter, correct wiring diagram
Disconnect the injector and disconnect the harness at the module, then check the control wire against engine ground, and check continuity from the injector connector to the correct module pin.
ExpectedNo continuity to ground, and near-zero resistance from connector to module pin. Continuity to ground proves the short — then inspect the entire run for the rub point.
Observe injector control patterns and compare with a healthy cylinder
Tools Lab scope, or a noid light for a quick check on port injection
Watch the drive pattern on cylinder 1 against a known-good cylinder while cranking or running. Look for a missing pulse, a pin stuck low, or a distorted waveform.
ExpectedA clean pulse with a normal inductive kick, matching the other cylinders. Do not use a noid light or backprobe on a direct-injection injector circuit — those carry high voltage that can injure you and damage the module.
Swap the suspect injector with one from a known-good cylinder, then clear and retest
Tools Basic hand tools, fuel pressure relief equipment, fire extinguisher, new injector seals (new high-pressure seals and hardware on DI), torque wrench, scan tool with injector coding capability where applicable
On port injection: relieve fuel system pressure and disconnect the battery before opening any fuel connection, keep an extinguisher within reach, and fit new O-rings on reassembly. Move the injector, not the connector, then clear the codes, run the engine, and see where the fault reports. On direct injection, do not treat this as a driveway test — relieve high-pressure fuel first, use new one-time high-pressure seals and hardware, observe the manufacturer's torque procedure, and check whether the vehicle stores per-cylinder injector calibration or correction codes. If it does, those codes must move with the injector or be relearned with a scan tool, or the swap will create fueling faults of its own and make the result unreadable. Where injector coding applies, prefer resistance comparison, waveform comparison, and a wiring check over a physical swap.
ExpectedIf the code follows the injector to the other cylinder, the injector is the fault. If it stays on cylinder 1, the fault is in the wiring or the module. Never reuse high-pressure DI seals, and always fit new O-rings when moving a port injector.
Evaluate the module's injector driver only after the injector and wiring are proven
Tools Lab scope, wiring diagram
With a known-good injector fitted and the wiring verified end to end, check for drive activity at the module pin itself.
ExpectedNormal drive activity at the module pin. No activity, or a pin held low, with everything upstream proven good points at a failed driver inside the module.
Check the engine oil for fuel dilution before returning the vehicle to service
Tools Nothing beyond the dipstick
Pull the dipstick, check for level above full and a fuel smell. If the injector was stuck flowing, the oil is contaminated.
ExpectedOil at normal level with no fuel odor. Fuel-diluted oil must be changed regardless of service interval — it has lost load-carrying capability.
| Repair | Only after you confirm | Typical cost | Who |
|---|---|---|---|
| Repair the chafed or shorted injector control wiring | Continuity measured from the control wire to ground with both ends disconnected, or a fault that appears only when a specific harness section is flexed or heated | $100–$450 | DIY |
| Replace the injector connector body or its terminals | Melted, spread, or corroded terminals found, or measurable resistance across the connector itself | $100–$300 | DIY |
| Replace the cylinder 1 port fuel injector | Winding resistance clearly out of line with the other injectors, or the code following the injector when swapped to another cylinder | $200–$600 | DIY |
| Replace the cylinder 1 direct-injection injector | Winding resistance or waveform clearly out of line with the other injectors, verified against the manufacturer's specific high-pressure injector test procedure, with new seals and any required injector coding performed on installation | $350–$1,000 | Hard |
| Repair or replace the engine control module and program it | A known-good injector fitted and wiring verified end to end, with the module still producing no drive or holding the pin low at its own connector | $600–$2,000 | Shop |
| Change engine oil and filter for fuel dilution | Oil level above full with a fuel smell on the dipstick after the injector has been leaking or stuck open | $60–$150 | DIY |
US independent shop rates, parts plus labor. Port injector jobs vary with access — some sit under an intake manifold that must come off, which can double the labor. Direct-injection injectors cost considerably more, often require special tools, new high-pressure seals, and scan-tool injector coding after fitting. Module replacement almost always includes programming and sometimes immobilizer relearn. If the engine was cranked against liquid fuel in a cylinder, internal engine damage is a separate and much larger cost.
- Replacing the injector without either a resistance comparison or a swap test. The circuit is just as likely to be the fault as the part.
- Opening a fuel connection without relieving system pressure and disconnecting the battery. A pressurized rail sprays fuel onto a hot engine.
- Physically swapping direct-injection injectors without moving or relearning the per-cylinder calibration codes, which creates new fueling faults and makes the swap result meaningless.
- Missing a chafed harness because it only shorts when hot, or only when the engine rocks under load. Test with the engine running and moving.
- Backprobing or noid-lighting a direct-injection injector circuit. The voltages involved are dangerous and can destroy the module's driver.
- Assuming the physically first injector on the rail is cylinder 1. Numbering varies and is worth thirty seconds of confirmation.
- Cranking an engine that has been sitting with a stuck-open injector without first checking for liquid fuel in the cylinder.
- Repairing the circuit while ignoring fuel-diluted oil, so the engine goes back into service on contaminated lubricant.
- Fitting a new injector into a circuit that still has a short to ground, and destroying the module's driver in the process. Prove the wiring before you fit the part.
- Fuel Injector
- Injector Wiring
- Ecu Injector Driver
- Definition
- Generic code set (SAE J2012 / ISO 15031-6) via the OBDexopen database, dedicated to the public domain under CC0-1.0.
- Diagnostic guidance
- Written and reviewed in-house. See our editorial policy.
- Review status
- Reviewed
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