What Is Car Fault Code P0278? Diagnose & Clear It with iCarsoft CR Pro S

If your check engine light illuminates and your diagnostic tool retrieves P0278, you’re facing an issue with your vehicle’s Fuel Injector Circuit—specifically a “High Input” malfunction for Cylinder 6. Fuel injectors deliver precise fuel amounts to engine cylinders, and this code signals an abnormal voltage or signal in the 6th cylinder’s injector circuit. Ignoring P0278 can lead to rough idling, reduced engine power, increased fuel consumption, or even cylinder misfires. In this guide, we’ll break down what P0278 means, why it occurs, and how the iCarsoft CR Pro S—your all-in-one diagnostic solution—can help you resolve it efficiently.

iCarsoft CR Pro S testing fuel injector circuit & cylinder 6 to diagnose P0278 fault code

What Exactly Is Fault Code P0278?

P0278 is a generic OBD-II trouble code defined as “Fuel Injector Circuit High Input (Cylinder 6)”. The ECU (Engine Control Unit) monitors the electrical signal of each fuel injector to ensure proper operation. When it detects a voltage signal from the 6th cylinder’s injector circuit that exceeds the normal operating range, it triggers P0278—indicating a malfunction in the injector, wiring, or related components.

This code applies to gasoline and diesel vehicles with electronic fuel injection systems. Left unaddressed, it may cause the ECU to deactivate the affected cylinder, further reducing performance and risking engine damage.

Why Does P0278 Happen? Common Causes

P0278 typically stems from issues with the 6th cylinder’s fuel injector, its circuit, or related components:

• Faulty Fuel Injector: Internal electrical failure or clogging causes abnormal signal output.
• Wiring/Connector Issues: Damaged, frayed, or shorted wires, or a loose/corroded connector between the injector and ECU.
• Short Circuit in the Injector Circuit: A short to power pulls the injector signal to an abnormally high voltage.
• Failed Fuel Injector Driver: The component in the ECU that controls the injector’s signal malfunctions.
• Poor Electrical Ground: A weak or damaged ground connection disrupts normal circuit voltage.
• Fuel System Issues: High fuel pressure or contaminated fuel strains the injector, triggering circuit errors.

Why the iCarsoft CR Pro S Is Ideal for P0278

When it comes to diagnosing and fixing P0278, the iCarsoft CR Pro S outperforms basic scanners by offering deep fuel system insights and global compatibility. Here’s why it’s your best tool:

How to Diagnose & Fix P0278 with the CR Pro S (Step-by-Step)

1. 1. Connect the CR Pro S

   Plug the tool into your car’s OBD-II port (under the dashboard) and turn on the ignition.

2. 2. AutoVIN Identify

   The tool automatically detects your vehicle’s details—no manual entry needed.

3. 3. Scan for Codes

   Select “Full System Scan” or “Engine System Scan” to retrieve P0278 and related codes (e.g., P0206 for injector circuit malfunction, P0306 for cylinder 6 misfire).

4. 4. Check Live Data

   Monitor the 6th cylinder’s injector voltage and cylinder balance—consistently high voltage (outside manufacturer specs) confirms a circuit or component problem.

5. 5. Test Components

   Use bi-directional control to activate the 6th cylinder’s injector—no response with intact wiring points to a faulty injector; fluctuating voltage with wire movement indicates wiring issues.

6. 6. Fix the Root Cause

   Replace the 6th cylinder’s fuel injector, repair wiring, fix electrical grounds, or service the fuel system (based on your findings).

7. 7. Clear the Code

   Use the “Erase Codes” function to reset P0278 and the check engine light.

8. 8. Re-Scan & Verify

   Run a follow-up scan after driving to ensure the code doesn’t return—confirm the fuel injector circuit is working properly.