An injector that never gets its power, or one whose control wire is shorted to ground, cannot work as the engine computer intends. A P0270 code means the computer saw a voltage lower than expected on the fuel injector circuit for cylinder 4.
This guide explains what the computer checks on the injector circuit, where cylinder 4 sits on common engines and how to test the circuit in the right order.
P0270 Code Breakdown
Every OBD-II code follows the same five-character pattern set by the SAE J2012 standard. Each character narrows down which system has the fault. This table shows what each part of the code tells you.
| Character | Meaning | What It Tells You |
|---|---|---|
| P | Powertrain | The fault is in the engine or transmission systems. |
| 0 | Generic (SAE) code | The definition is the same on every OBD-II vehicle. |
| 2 | Fuel and air metering | The fault involves fuel and air metering, such as injectors, the fuel pump, throttle sensors or boost control. |
| 70 | Specific fault | Cylinder 4 Injector Circuit Low |
What the P0270 Code Means
The SAE J2012 standard defines the P0270 code as Cylinder 4 Injector Circuit Low. On most port injection engines, each injector gets battery voltage from a fuse or relay whenever the engine runs. The powertrain control module (PCM) opens the injector by grounding its control wire for a few milliseconds.
With the injector off, the PCM expects to see battery voltage on the control wire, passed through the injector coil. When it switches the driver on, it expects the voltage to drop close to 0 volts, and when it lets go, it expects a sharp voltage spike as the coil releases.
A low reading means the control wire voltage stayed low when it should have been high. That usually points to a lost power feed, a control wire shorted to ground or a shorted injector coil. A control wire shorted to ground can hold the injector open and flood the cylinder.
On inline four engines, cylinder 4 is at the back, nearest the transmission. On GM and Chrysler V8s, it is second on the passenger side, and on Ford V8s it is the rear cylinder on the passenger side. Numbering varies by maker, so always confirm the layout in your service manual.
Symptoms of a Cylinder 4 Injector Circuit Fault
Cylinder 4 may get no fuel, or too much. Common signs of a P0270 code include:
- Check engine light on, sometimes flashing
- Misfire code P0304 for cylinder 4
- Rough idle and shaking
- Loss of power
- Fuel smell from the exhaust
- Hard starting from a flooded cylinder
Common Causes of the P0270 Code
These are the usual causes:
- Lost injector power feed. A blown fuse, failed relay or broken feed wire.
- Control wire shorted to ground. Chafed insulation touches the engine or a bracket.
- Shorted injector coil. Very low coil resistance pulls the voltage down.
- Corroded connector. Moisture creates a path to ground.
- PCM driver fault. Rare.
Tools You Will Need
You can do most of this testing at home with basic tools:
- OBD-II scan tool with misfire counts
- Digital multimeter and test light
- Noid light set for port injection engines
- Back-probe pins
- Wiring diagram and cylinder layout for your engine
How to Diagnose the P0270 Code
Confirm which cylinder is cylinder 4 on your engine first. Then work from the connector toward the PCM.
Inspect the Connector and Wiring
Find the cylinder 4 injector and check that its connector is fully seated and locked. Look for corrosion, oil inside the plug and wires that are flattened, shiny or melted where they touch metal.
Check Power at the Connector
Unplug the injector and turn the key on. One pin should light a test light grounded to the battery. If neither pin has power, check the injector fuse, relay and feed wire. Several injector codes at once point to a shared feed.
Measure Injector Resistance
Measure across the injector terminals. Most high-impedance port injectors read about 11 to 18 ohms, and low-impedance types read about 2 to 5 ohms. Compare it with the other injectors. A reading near zero means a shorted coil.
Test the Control Wire
With the battery disconnected and the PCM unplugged, check the control wire for a short to ground. Any continuity means a short. Check the wiring where it passes brackets and the intake.
On port injection engines, a noid light at the connector should flash while cranking. You can also swap the injector with a neighbor. If the code follows the injector, replace it.
How to Fix the P0270 Code
Match the repair to what your tests found. Then clear the code and drive under the same conditions that set it.
- Repair the connector or wiring and protect the wires from heat and sharp edges.
- Replace a blown fuse or failed relay after finding what caused it.
- Replace the cylinder 4 injector if its resistance is out of range. Use new O-rings or seals.
- Repair or replace the PCM only after the wiring and injector test good.
On direct injection and diesel engines, injectors are driven at high voltage and may need coding to the engine computer after replacement. Follow the service manual, and do not use a standard noid light on these systems.
Common Mistakes to Avoid
These mistakes waste money or leave the real fault in place:
- Replacing the injector before checking power and the connector
- Testing the wrong cylinder because numbering was assumed
- Clearing the P0304 misfire and ignoring the circuit code
- Installing a new PCM without checking for a shorted injector
Repair Cost Breakdown
The cost to fix a P0270 code depends on the cause. This table shows typical ranges for parts and labor.
| Repair | DIY Cost | Typical Shop Cost |
|---|---|---|
| Connector or pigtail | $15 to $40 | $100 to $250 |
| Wiring repair | $10 to $30 | $100 to $350 |
| Gasoline port injector | $40 to $150 | $150 to $500 |
| Diesel injector | $200 to $600 | $400 to $1,200 |
| PCM repair or replacement | $200 to $800 | $500 to $1,500 |
Access matters as much as parts. A front injector on a four-cylinder engine may take minutes, while a rear injector under a V8 intake can take hours.
Is It Safe to Drive with a P0270 Code?
It is best not to. A dead cylinder misfires, and the unburned fuel and air can overheat the catalytic converter. A control wire shorted to ground can hold the injector open and wash fuel into the oil.
If the check engine light flashes, stop driving as soon as it is safe. If it is steady, drive gently and only as far as a repair shop.
Related Codes
These codes often show up with this one or point to the same system:
| Code | Meaning |
|---|---|
| P0271 | Cylinder 4 Injector Circuit High |
| P0272 | Cylinder 4 Contribution/Balance Fault |
| P0204 | Injector Circuit Malfunction, Cylinder 4 |
| P0304 | Cylinder 4 Misfire Detected |
| P0200 | Injector Circuit Malfunction |
| P0300 | Random/Multiple Cylinder Misfire Detected |
Fixing the Cylinder 4 Injector Circuit
A P0270 code means the PCM saw the cylinder 4 injector circuit voltage read low. Lost power feeds, shorts to ground and shorted injectors cause most cases.
- Confirm which cylinder is cylinder 4.
- Inspect the connector and wiring.
- Check power and measure injector resistance.
- Test the control wire for shorts to ground.
Frequently Asked Questions
What Is the Difference Between the P0270 Code and P0271?
Both point to the cylinder 4 injector circuit. The P0270 code means the PCM saw a low voltage, while P0271 means it saw the opposite. Low readings usually mean a short to ground or lost power. The tests are similar, but the likely causes differ.
Can a Bad Injector Set the P0270 Code?
Yes. A shorted coil pulls the circuit voltage low. Measure the injector resistance and compare it with the others. A reading far from the rest confirms a bad injector.
Can I Swap Injectors to Test Them?
Yes, on most port injection engines. Move the cylinder 4 injector to another cylinder and clear the codes. If the code moves with the injector, replace it. If it stays on cylinder 4, the wiring or PCM is at fault.
Will Injector Cleaner Fix This Code?
No. Cleaner helps clogged nozzles, but this code points to an electrical fault. A shorted or open coil, a broken wire or a bad connector will not respond to cleaner.
How Long Does the Repair Take?
A connector or wiring repair near an easy-to-reach injector can take under an hour. A rear injector under a V engine’s intake manifold may take two to four hours. Diesel and direct injection injectors often take longer, since the fuel system must be depressurized first.
Is This Code Common on Diesels?
It appears on diesels and direct injection engines too. Those injectors run on high voltage, so testing is different and must follow the service manual. Some also need injector codes programmed into the engine computer after replacement.