OBD codes / P0270
P0270
ModerateCylinder 4 Injector Circuit Low
With its injector circuit faulted, cylinder 4 may run dead or erratic, and the unburned fuel it passes downstream can overheat the catalytic converter. It's usually fine to drive gently to a shop, but don't put the repair off — and a flashing check-engine light means stop and get it looked at now.
What this code means
Behind every injector pulse is a monitored circuit, and P0270 means the ECM caught the cylinder 4 injector circuit reading below its expected voltage. The likely faults are a wire shorted to ground, an open somewhere in the circuit, or an injector coil that has shorted internally and now draws too much current. None of these involve fuel contamination or clogging — a blocked nozzle is a mechanical problem that sets misfire codes, not circuit codes, so skip the fuel additives here. With only cylinder 4 implicated, the quickest diagnostic move is comparing its injector resistance and wiring condition against any healthy cylinder. Expect P0204 (cylinder 4 injector circuit) or P0304 (cylinder 4 misfire) as companions when the injector actually stops firing. Cylinder 4's physical location depends on the engine layout and manufacturer numbering, so verify it against your engine's diagram first.
Symptoms you might notice
- Misfire concentrated on cylinder 4
- Rough idle, shaking, or an uneven exhaust note
- Hesitation and power loss under acceleration
- Check-engine light, potentially flashing during heavy misfire
- Can be symptom-free when the fault is 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 |
Harness and connector repairs are inexpensive parts-wise; you're mostly paying for diagnostic time. Injector replacement is the costlier outcome, more so on V-type engines requiring intake removal and on direct-injection engines.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P0270 for my exact vehicle →
Frequently asked
Is P0270 an electrical problem or a fuel problem?
Electrical. The ECM is reporting that the cylinder 4 injector's control circuit voltage dropped below its expected range — pointing at wiring, the connector, the injector's coil, or rarely the ECM driver. Fuel quality and injector-cleaning additives are not relevant to this code.
What's the fastest way to diagnose P0270?
Unplug the cylinder 4 injector and measure its resistance, then compare it with another cylinder's injector. Matching readings shift suspicion to the harness and connector; a shorted or open reading condemns the injector. A swap test with a neighboring cylinder confirms it.
Can driving with P0270 hurt the car?
The main risk is the catalytic converter: a cylinder that isn't burning fuel dumps it into the exhaust, where it can overheat the converter. Brief, gentle driving is usually okay, but sustained driving with an active misfire is how converters get ruined.
Why do P0270 and P0271 both mention cylinder 4?
They're two directions of the same monitor. P0270 sets when the circuit voltage runs low (short to ground, shorted coil); P0271 sets when it runs high (open circuit, corrosion, short to battery). Which one you have tells the technician where to start looking.
Seeing P0270 on your car? Get a diagnosis specific to your exact year, make and model.
Diagnose P0270 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.