P0271 code: Cylinder 4 Injector Circuit High
P0271 means cylinder 4 Injector Circuit High. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0271 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.
P0271 symptoms
- 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 P0271
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 →
How to fix P0271
Moderate — doable at home with common tools and patience
- Clear the code and watch how fast it returns
Erase P0271 and start the engine. If it resets within seconds every time, expect a solid fault — an open winding, a broken wire or a short to power. If it takes days or only appears after rough roads, focus on connections that break with vibration and engine rock rather than on the injector.
- Back-probe the driver at the module
With a scope, or a meter that reads duty cycle, compare the cylinder 4 driver pin at the module with a healthy cylinder's pin while idling. Normal switching at the module but a missing pulse at the injector means a break in between; no switching at the module may just mean it has shut down a faulted driver, so clear codes and recheck.
- Check injector 4's resistance against a known-good one
Unplug injector 4 and its neighbour and read both. If injector 4 shows OL or sits well above the other — healthy high-impedance injectors usually measure somewhere in the 11–18 ohm band — the winding is the fault. Equal readings move the hunt to the connector and harness.
- Look for fluid or corrosion at the end connector
On some engines the cylinder 4 connector sits below a thermostat housing, coolant outlet or valve-cover corner, and a slow leak there wicks into the terminals. Green crust or oily pins add resistance that reads as circuit high; clean with contact cleaner, fix the leak, and replace the pigtail if the terminals are pitted.
- Fit a repair pigtail and verify
A replacement injector pigtail spliced in with solder and heat-shrink restores proper terminal tension and sealing. Clear the codes, drive through a cold start, a full warm-up and some rough pavement, then rescan to confirm P0271 and any P0304 stay away.
DIY or shop? Most of this is home-mechanic work: clearing and watching the code, reading resistance, and cleaning or replacing a pigtail need only a meter and basic wiring skills. The module back-probe test needs a scope and a pinout, and it's the step most DIYers skip — that's fine, but if a new pigtail and good injector readings don't fix it, stop there and let a shop with wiring diagrams check the driver rather than buying a module.
Tools for the DIY steps: OBD-II scan tool · Digital multimeter · Lab scope or duty-cycle meter · Electrical contact cleaner · Injector connector pigtail · Soldering iron and heat-shrink
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0271.
Start a case with P0271 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P0271?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0271: common questions
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?
It can, 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?
A code alone can't settle that, but the repair is a days-not-weeks job. 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: stop driving.
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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0271 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P0271 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.