P0270 code: Cylinder 4 Injector Circuit Low
P0270 means cylinder 4 Injector Circuit Low. The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P0270 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.
P0270 symptoms
- 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 P0270
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 →
How to fix P0270
Moderate — doable at home with common tools and patience
- Locate cylinder 4 at the far end of the head
On inline fours, cylinder 4 is usually the last one, at the transmission end opposite the timing drive. Three-cylinder engines don't have one, and V engines place it differently depending on the manufacturer's numbering, so confirm with a diagram before unplugging anything.
- Read spark plug 4 for signs of flooding
A control wire shorted to ground can keep injector 4 open whenever its feed is live, dumping raw fuel. Pull plug 4 and compare it with another cylinder: a fuel-soaked plug, a fuel smell on the dipstick, or hard starting after shutdown backs that up. If you see it, avoid long cranking until the short is found.
- Ohm-test the winding and the wire to ground
Measure injector 4 against its neighbours — a reading well under the group (typical high-impedance values cluster around 11–18 ohms) means shorted turns. Then, with the battery and module unplugged, check the control wire to ground; continuity there means the harness, not the injector, is pulling the circuit low.
- Scope the injector current if the meter is inconclusive
A low-amp clamp on the injector 4 circuit shows the current ramp each time it fires. Compared with a healthy cylinder, a shorted winding climbs faster and peaks higher, which can expose an injector that measures close to spec at rest but misbehaves under load and heat.
- Replace the faulty part and verify the driver
Replace injector 4 or repair the wire, whichever tested bad, then clear codes and confirm the misfire count stays at zero. If a new injector and a clean harness still set P0270, the module's driver is suspect; that means a module replacement with programming, so have it confirmed by a shop first.
DIY or shop? With cylinder 4 usually at the end of the head, its plug and connector are often among the easier ones to reach, so the flooding check and resistance tests are fair game for most owners. Replacing a port injector is moderate DIY if you relieve fuel pressure, keep sparks away and use new seals, and if plug 4 showed flooding, change the oil afterwards. The current-clamp test and a suspected module driver fault are shop territory for most people.
Tools for the DIY steps: Spark plug socket · Digital multimeter · Low-amp current clamp and scope · Fuel pressure gauge with bleed valve · Injector seal kit
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P0270.
Start a case with P0270 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 P0270?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P0270: common questions
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. Every mile with an active misfire adds to that damage, so get it repaired promptly, and stop driving if the light flashes.
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.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P0270 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 P0270 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.