P0270
PowertrainCylinder #4 Injector Circuit Low
The ECU fires each injector by switching its electrical circuit, and it watches the voltage and current on that line to make sure the injector is responding. When the cylinder 4 injector circuit reads too low, usually a short to ground or a dead circuit, the ECU logs P0270. For you as the owner, that means cylinder 4 either isn't getting its fuel pulse properly or there's a wiring fault feeding it, and the engine runs down on one cylinder until it's sorted.
ⓘ Information only. This page provides general educational information about fault code P0270. 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 P0270 mean?
P0270 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Cylinder #4 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, sometimes with the car dropping into limp mode
- • Lumpy, uneven idle that's worse from cold and can smooth out a bit once warm
- • Noticeable flat spot or hesitation when you put your foot down
- • Fuel economy drops because cylinder 4 isn't pulling its weight
- • A misfire feel through the gearbox or steering wheel at idle and low revs
- • Harder starting, particularly on a cold morning
Possible causes
Causes commonly associated with P0270, listed in approximate order of typical investigation. The actual cause on a specific vehicle can only be confirmed by professional diagnosis.
- 1. Failed or shorted injector on cylinder 4, the winding inside has gone down to ground or open. This is the most common single part to blame
- 2. Corroded or damaged wiring at the injector, common where heat and road muck attack the loom near the head
- 3. Loose or backed-out pin in the injector connector, so the contact is intermittent or shorting
- 4. Chafed harness shorting to ground where it rubs against a bracket, the rocker cover, or the block
- 5. ECU injector driver gone down on that channel, less common but it does happen on high-mileage cars
- 6. Wiring fault upstream such as a damaged section of loom or a poor earth affecting the injector feed
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. Read live data and freeze frame, then check whether any cylinder 4 misfire codes (P0304) are stored alongside it. That tells you straight away if the cylinder is actually dead or just flagging an electrical fault
- 2. Unplug the injector connector and inspect it properly. Look for green corrosion, melted pins, spread terminals, and oil tracking into the plug, which is a classic cause on petrol fours
- 3. Measure the injector resistance with a multimeter across its two pins and compare to spec. Most petrol injectors sit around 12 to 16 ohms, a reading near zero confirms a shorted winding
- 4. Test the wiring back from the connector for a short to ground and for continuity to the ECU, wiggling the loom as you go to catch an intermittent
- 5. Swap the cylinder 4 injector with one from another cylinder. If the fault moves to the new cylinder, the injector is your culprit. If it stays on 4, the problem is in the wiring or the ECU
- 6. Only if injector and wiring both check out clean, look at the ECU injector driver as the last suspect
Common questions about P0270
How do I know if it's the injector itself or just the wiring? +
The resistance test sorts most of it. Unplug the cylinder 4 injector and measure across its pins, a healthy petrol injector usually reads around 12 to 16 ohms. Near zero means a shorted injector, an open reading means a broken winding. If the injector reads fine, the fault is in the loom or connector, so check for chafing, corroded pins, and a short to ground. The swap test backs this up: move the injector to another cylinder and see if the code follows it.
How long is this in the garage for? +
A connector or wiring repair is often under an hour once they've traced it, the time goes into finding the fault rather than fixing it. Replacing an injector is usually an hour or two on a typical petrol four, longer on engines where the inlet manifold has to come off to reach the rail. ECU work or a tricky intermittent short can stretch a job into half a day because diagnosis is the slow part.
Is a cheap aftermarket injector worth fitting or should I stick with OEM? +
For an everyday car a quality branded aftermarket injector from a known parts maker is fine and a lot cheaper than dealer OEM. Where I'd steer clear is the no-name eBay specials, because a poorly flow-matched injector can leave you with a rough running cylinder even with no fault code. If you're only replacing one injector, get it flow-matched to the others if you can, otherwise the new one may not deliver the same as its neighbours.
Can I keep driving with this? +
Short hops to get it looked at, yes, but don't make a habit of it. Running on three good cylinders pumps unburnt fuel into the exhaust, and that cooks the catalytic converter, which is a far dearer fix than the injector. If the car has dropped into limp mode you'll have very little power anyway. Get it sorted promptly rather than living with it.
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 →