OBD-II trouble code
P0270: Cylinder 4 Injector Circuit Low
The cylinder 4 injector control circuit read low — usually a wire shorted to ground or a shorted injector coil. The cylinder typically misfires, so diagnose it before the catalytic converter is damaged.
Quick facts
- System
- Powertrain
- Category
- Fuel Injectors
- Severity
- Medium severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $50 – $1,500
- DIY difficulty
- Intermediate DIY
What does P0270 mean?
The engine control module (ECM) controls each fuel injector on the ground side. Switched battery voltage sits on one injector terminal, and the ECM fires the injector by pulling the other terminal to ground for a precisely metered pulse width. Between pulses that control wire should read close to battery voltage, because nothing should be tying it to ground.
P0270 sets when the ECM sees the cylinder 4 control circuit reading low when it expects high. The circuit is grounded when it should be floating. In practice that means a control wire that has chafed through and touched the block or a bracket, an injector with a shorted coil winding, or corrosion and moisture bridging pins inside the connector. On some platforms the code also sets when the measured current through the circuit is below the expected range.
What follows electrically is straightforward: cylinder 4 is not being fueled the way the ECM intends, so a misfire is likely and P0304 often appears alongside. That misfire is the reason this code deserves prompt attention. Raw air and unburned fuel entering the exhaust can superheat the catalytic converter, and replacing a converter costs far more than repairing a wire or an injector.
A note that matters on four-cylinder and V-configuration engines alike: cylinder 4 is the manufacturer's cylinder 4, which is not necessarily the fourth injector from the front of the engine bay. On an inline four it usually is, at the rear of the engine near the firewall — but on a V6 or V8 it may be on the opposite bank from where you would guess. Confirm the numbering in the service information before you begin testing.
Common causes
- Cylinder 4 injector control wire chafed through and shorted to ground
- Shorted coil winding inside the cylinder 4 injector
- Corrosion or water intrusion bridging terminals in the injector connector
- Harness insulation heat-damaged near the exhaust manifold or turbocharger
- Wire pinched during a prior intake manifold, valve cover, or timing repair
- Damaged, spread, or backed-out terminal in the injector connector
- Rarely, a failed cylinder 4 injector driver circuit inside the ECM/PCM
Symptoms
- Check engine light on, sometimes flashing under load
- Rough idle with a noticeable engine shake
- Misfire on cylinder 4, commonly with a companion P0304
- Loss of power and hesitation under acceleration
- Raw fuel smell from the exhaust
- Increased fuel consumption
- Hard starting in some cases
Diagnostic steps
- 1.Confirm P0270 and record all companion codes. A cylinder 4 misfire (P0304), the paired high code P0271, or a balance fault (P0272) each shift the diagnostic emphasis.
- 2.Identify cylinder 4 for your specific engine before touching anything — on a V engine it may sit on the opposite bank from where you expect.
- 3.Inspect the cylinder 4 injector connector and pigtail for corrosion, melted or hardened insulation, and backed-out terminals. On an inline four this connector sits near the firewall and collects moisture and heat.
- 4.With the key off, unplug the injector and measure its coil resistance. Compare it to specification and to the other three injectors — a reading well below spec confirms a shorted coil.
- 5.Disconnect both the injector and the ECM connector, then check the control wire for continuity to ground. Any continuity confirms a short in the harness rather than a bad injector.
- 6.Wiggle-test the harness from the injector back toward the firewall, focusing on chafe points near the exhaust manifold, manifold studs, and any hard bracket edges.
- 7.With the wiring and injector verified good, use a noid light or the scan tool's injector test to confirm the ECM is pulsing the circuit normally.
- 8.If everything external tests correct and the drive signal is still wrong, suspect the ECM injector driver — verify with the manufacturer's pinout test before condemning the module.
Repair cost
$50 – $1,500
Repairing a chafed wire or a corroded connector is often $75-$250. A single fuel injector is $60-$400 in parts plus 0.5-3 hours of labor — an accessible port injector is quick, while a direct-injection or under-manifold injector takes considerably longer. A failed ECM injector driver is uncommon and runs $500-$1,500 including programming. Diagnosis alone is typically $75-$150.
Estimate your repair
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Open the Repair Cost Estimator with fuel injector replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.