P0261
PowertrainCylinder #1 Injector Circuit Low
Most of the time this comes down to a dodgy connection at the cylinder 1 injector, either a corroded plug or a chafed wire, rather than the injector itself being dead. The ECM drives each injector by switching its earth side, and it watches the voltage on that circuit. When it sees the voltage drop too low, meaning the circuit is shorted to earth or the injector isn't switching properly, it logs P0261 and points the finger at cylinder 1.
ⓘ Information only. This page provides general educational information about fault code P0261. We do not assess the urgency or safety implications of any specific fault. That requires in-person diagnosis by a qualified mechanic. Full terms.
Recommended next steps
Whether a fault is urgent, drivable, or routine depends entirely on the cause on a specific vehicle, and that can only be determined by a qualified mechanic with diagnostic equipment. If a warning light is illuminated, the most reliable next step is professional diagnosis.
What does P0261 mean?
P0261 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder #1 Injector Circuit Low.
This is a standardised OBD-II code. The technical definition is the same regardless of the make or model of vehicle, although specific causes and symptoms can vary between vehicles.
Symptoms commonly associated with this code
Symptoms that drivers often report alongside this code. Not all may apply to every case:
- • Engine warning light on, often the first thing the owner notices
- • Lumpy idle, the engine shaking or hunting when sat at the lights
- • A clear misfire on cylinder 1, sometimes felt as a tap or stumble through the pedal
- • Hesitation or a flat spot when you put your foot down, worse under load
- • Fuel economy creeping up because cylinder 1 isn't burning cleanly
- • On some cars the ECM drops into limp mode to protect the engine
Possible causes
Causes commonly associated with P0261, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Corroded, loose or backed-out pins in the injector connector. This is where I'd put my money first, water and road salt get into these plugs and ruin them
- 2. Chafed or broken wiring in the injector harness, often rubbing through where the loom is clipped against the head or a bracket
- 3. Poor earth, the ECM switches the injector earth side so a bad ground or corroded strap will mimic an injector fault
- 4. The injector itself shorted internally, resistance gone out of range. Common on high-mileage diesels
- 5. A blocked or sticking injector pulling odd current, less common as a P0261 trigger but it happens
- 6. Low system voltage from a tired battery or failing alternator confusing the injector driver
- 7. Faulty ECM injector driver circuit, the rarest cause and the one to leave till last
How mechanics typically diagnose
A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training.
- 1. Pull the codes and look at the freeze frame data. Note whether the fault came in cold, warm, or under load, that tells you a lot before you touch a spanner
- 2. Unplug the cylinder 1 injector connector and inspect it properly. Look for green corrosion, spread or pushed-back pins, and check the locking tab actually holds. Wiggle the loom while watching for the fault to come and go
- 3. Check for 12V on the feed side of the connector with the ignition on. Power present means the supply is fine and the problem is downstream
- 4. Measure the injector resistance across its terminals with a multimeter. Petrol injectors usually sit around 12 to 16 ohms, diesels are much lower, so check the figure for your engine before condemning it
- 5. Test the earth side back to the ECM for continuity and resistance, and check the engine earth strap while you're under there
- 6. If the connector, wiring, injector and earth all check out, the ECM driver is the suspect. Don't jump to that until everything cheaper is ruled out
Common questions about P0261
Can I keep driving it or should I park it up? +
You can usually drive it, but I wouldn't make a habit of it. With cylinder 1 misfiring you're pumping unburnt fuel into the exhaust, and that cooks the catalytic converter, which turns a wiring repair into a much bigger bill. If the car has gone into limp mode or it's really stumbling, get it looked at before you do any long motorway runs. A short trip to the garage is fine. A week of commuting on it is asking for trouble.
Is this going to fail my MOT? +
The code on its own isn't a fail, but if the engine warning light is glowing on the dashboard when the tester looks at it, that's an automatic MOT fail under the current rules. A persistent misfire can also push you over on the emissions side for petrol cars. Fix the fault, clear the light, and let the car run a few drive cycles so the lamp stays off before the test.
What's this likely to cost me? +
If it turns out to be a connector clean-up or a small wiring repair, an independent garage will sort it for a low three-figure sum including the diagnostic time. A new injector fitted is more like £150 to £400 depending on the engine, with diesel common-rail injectors at the top end. A main dealer will charge a fair bit more on labour, often £120 an hour plus. Reprogramming or replacing the ECM is the worst case and can run into four figures, but that's the least common outcome.
How do I work out which cause it actually is on my car? +
Start at the injector plug. If you find corrosion or a loose pin and the fault clears after cleaning and reseating it, you've found it, no need to spend more. If the connector is clean and you've got 12V on the feed but the injector resistance reads out of spec or open, the injector is gone. If both the connector and injector are fine, you're chasing a wiring or earth fault, and wiggling the loom while the engine runs will often make the misfire flicker right where the wire has rubbed through.
Information only, not professional advice
The information on this page is provided for general guidance and educational purposes only. It is not a substitute for diagnosis or repair advice from a qualified mechanic. Always verify any fault before paying for repairs. carfaultcodes.co.uk accepts no liability for decisions made based on this information. Full terms →