P0268

What Does Code P0268 Mean?

DTC P0268 signifies a “Cylinder 3 Injector Circuit High” condition. This diagnostic trouble code is triggered by the Engine Control Module (ECM) or Powertrain Control Module (PCM) when it detects a voltage reading in the electrical control circuit for the #3 fuel injector that is higher than the predetermined operating parameters. The ECM actively monitors the resistance and voltage drop across each fuel injector circuit. A “high” condition typically indicates an open circuit within the injector wiring, an internal open in the injector’s solenoid winding, or an unwanted short to a voltage source within the control circuit. This fault directly impacts the fuel delivery system for cylinder #3, potentially leading to a lean air/fuel mixture, complete absence of fuel delivery to that cylinder, or erratic fuel injection, thereby compromising engine performance and emissions.

Common Symptoms

• Malfunction Indicator Light (MIL) illumination: The “Check Engine” light will be on.
• Engine misfire: Specifically on cylinder #3, resulting in noticeable rough idling, hesitation, and reduced power output.
• Reduced engine performance: A noticeable loss of acceleration and overall power.
• Poor fuel economy: The ECM may attempt to compensate, or incomplete combustion will lead to inefficiency.
• Rough idle or stalling: Particularly at low engine speeds or under load.
• Increased exhaust emissions: Due to unburnt fuel or an imbalanced air/fuel ratio.

What Causes the Code P0268?

• Open circuit in cylinder 3 injector wiring: A break, cut, or damaged insulation leading to an open circuit in either the power supply or control wire to the injector.
• Short to voltage in cylinder 3 injector wiring: The injector’s control wire or power supply wire is inadvertently contacting a higher voltage source (e.g., battery voltage) somewhere in the harness.
• Faulty cylinder 3 fuel injector: An internal open circuit in the injector’s electromagnetic coil or solenoid winding.
• Corroded, loose, or damaged electrical connector for cylinder 3 injector: Compromising the electrical connection and causing high resistance or an intermittent open.
• Faulty ECM/PCM: A defective injector driver circuit within the ECM/PCM for cylinder #3 (less common, but possible).

How to Diagnose and Troubleshoot

Begin diagnosis with a systematic approach using appropriate tools:

1. Visual Inspection: Begin by carefully inspecting the wiring harness and electrical connector for cylinder #3 fuel injector. Look for signs of chafing, cuts, corrosion, bent pins, or loose connections. Trace the wiring back from the injector to the ECM, checking for any visible damage.
2. OBD-II Scanner Check: Connect an OBD-II scanner to verify the presence of P0268 and check for any related misfire codes (e.g., P0303) or other fuel system codes. Clear the code and retest to see if it immediately returns, which can indicate a hard fault. Monitor live data for injector pulse width on cylinder #3 if available; a “high circuit” often results in no pulse or abnormal readings.
3. Digital Multimeter (DMM) – Key Off, Injector Disconnected:
   • Injector Resistance Test: Disconnect the electrical connector from cylinder #3 injector. Using a DMM set to ohms, measure the resistance across the two terminals of the injector itself. Compare this reading to the manufacturer’s specifications (typically 10-16 ohms for most multi-port fuel injectors). An infinite reading (OL) indicates an internal open circuit within the injector.
   • Wiring Continuity Test: With the injector disconnected, test for continuity from each wire in the injector harness connector back to the corresponding pins at the ECM connector (refer to vehicle-specific wiring diagrams). Look for any open circuits in the wiring.
   • Short to Ground Test: Measure resistance between each wire in the injector harness connector and a known good chassis ground. Both readings should show infinite resistance (OL). Any low resistance indicates a short to ground.
4. Digital Multimeter (DMM) – Key On, Engine Off (KOEO), Injector Disconnected:
   • Power Supply Test: With the injector connector still disconnected, turn the ignition to the KOEO position. Using the DMM set to DC volts, measure the voltage on the power supply wire (one of the two wires) at the injector harness connector. You should typically see battery voltage (around 12V). If no voltage, diagnose the power supply circuit (fuse, relay, wiring).
   • Control Circuit Test (Short to Voltage): Measure the voltage on the injector’s control wire (the other wire) at the harness connector. With KOEO, this wire should ideally be near 0V or fluctuating very low if the ECM is sending a test pulse. If you detect battery voltage (or significantly high voltage) on the control wire, it indicates a short to voltage on that circuit, as the ECM typically grounds this wire to fire the injector.
5. ECM Driver Test (Advanced): If all wiring and the injector itself test good, and the power supply is correct, the issue might be with the ECM’s internal driver for cylinder #3. This often requires specialized diagnostic equipment or substitution of the ECM, but this should be a last resort after ruling out all other possibilities.

Recommended Repairs and Solutions

Once the root cause has been identified through systematic diagnosis, the following repairs are commonly recommended:

• Repair or Replace Damaged Wiring/Connectors: If visual inspection or DMM tests reveal an open circuit, short to voltage, or corroded/damaged connector pins, perform precise wiring repair using heat-shrink butt connectors or replace the entire section of the harness if damage is extensive. Replace faulty connectors as needed.
• Replace Cylinder 3 Fuel Injector: If the injector itself fails the resistance test (infinite resistance or significantly out of specification), it indicates an internal coil failure. Replacing the faulty injector with a new, OEM-specification unit is the definitive solution. Always ensure proper O-ring lubrication and seating during installation to prevent fuel leaks.
• ECM/PCM Repair or Replacement: If all other components (wiring, connectors, and injector) test perfectly fine, and a definitive short to voltage is identified on the control wire that isn’t external, then the ECM’s internal injector driver circuit for cylinder #3 may be faulty. This is a complex repair, often requiring a professional with specialized programming tools to replace and program a new or remanufactured ECM.

Important Mechanics’ Tips:

• Always disconnect the vehicle’s battery terminals before performing any electrical work to prevent accidental shorts or damage to sensitive electronic components.
• After any electrical repair, apply a thin layer of dielectric grease to electrical connectors to prevent future corrosion and ensure a good electrical connection.
• Following any repair, clear the DTCs with an OBD-II scanner and perform a thorough test drive under varying load conditions to confirm the fix and ensure the code does not return.
• Consult manufacturer Technical Service Bulletins (TSBs) for your specific vehicle make and model, as some vehicles may have known issues or specific diagnostic procedures related to injector circuits.
• When replacing an injector, it’s often prudent to inspect the condition of the O-rings and pintle cap of other injectors, especially on high-mileage vehicles, as a preventative measure.