OBD codes / P0271
P0271
ModerateCylinder 4 Injector Circuit High
A cylinder 4 that fires unreliably passes raw fuel into the exhaust, and the catalytic converter can overheat if that continues. Keep driving minimal and gentle until the circuit is repaired; if the check-engine light flashes, treat it as a stop-driving signal.
What this code means
P0271 is the ECM reporting that voltage on the cylinder 4 injector circuit climbed above the expected range. High readings typically trace to a short to battery voltage, or to resistance that shouldn't be there — corroded connector pins, a frayed wire down to a few strands, or an injector winding that has failed open. Don't confuse this with a clogged injector: deposits restrict fuel flow but leave the electrical circuit looking normal, so they produce misfire codes rather than circuit codes. The cylinder-specific flag means you can benchmark everything against a healthy cylinder, and a simple injector swap test tells you whether the part or the wiring is at fault. Related codes to watch for are P0204 (circuit) and P0304 (misfire), both for cylinder 4. Since manufacturers number cylinders differently, confirm cylinder 4's location on your specific engine before servicing.
Symptoms you might notice
- Dead or stumbling cylinder 4
- Rough idle with noticeable vibration
- Power loss and increased fuel consumption
- Check-engine light, flashing under an active misfire
- Sometimes stored with no symptoms if intermittent
What it costs to fix
Typical range: $60–$450 · about ~0.5–2 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| Fuel injector (single) | $50–$300 | ~0.5–2 hrs |
| Wiring/connector repair | $5–$50 | ~0.5–2 hrs |
If the fix is a cleaned connector or repaired wire, cost stays low. A new injector raises it, and access drives labor: injectors buried under a V-engine's intake, or high-pressure direct-injection injectors, sit at the expensive end.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0271 for my exact vehicle →
Frequently asked
What does 'injector circuit high' mean in plain terms?
When the computer fired the cylinder 4 injector, the voltage on that circuit was higher than it should be. That happens when the wire touches battery voltage somewhere, or when corrosion or a failing injector winding adds resistance to the circuit.
Could a bad connector really cause this?
Yes, and it's common. Injector connectors live in a hot, vibrating environment, and oxidized or loose pins add exactly the kind of resistance that trips a circuit-high code. Inspecting and cleaning the connector is a free first step before replacing anything.
How long can I drive with P0271?
Think days, not weeks. The engine will usually run on the remaining cylinders, but unburned fuel from cylinder 4 can damage the catalytic converter — a much pricier repair than an injector or wire. A flashing light means the damage risk is immediate.
Why might P0271 appear only sometimes?
Intermittent circuit codes usually mean an intermittent connection: a corroded pin that conducts until vibration or heat breaks contact, or a chafed wire that touches ground or battery voltage only over bumps. Wiggle-testing the harness while watching live data often exposes it.
Seeing P0271 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0271 for my vehicleRelated trouble codes
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Generic OBD-II reference. Manufacturer-specific behavior varies — confirm with a scan tool and, for safety-related codes, a professional inspection.