P1268

What Does Code P1268 Mean?

DTC P1268 signifies an internal electrical malfunction within the circuit controlling the fuel injector for cylinder #8, specifically indicating a “High To Low Side Short.” In modern engine management systems, fuel injectors are typically supplied with a constant battery voltage (the “high side” or power supply) when the ignition is on. The Engine Control Module (ECM) or Powertrain Control Module (PCM) then controls the injector’s operation by providing a pulsed ground signal (the “low side” or control circuit) to complete the circuit, opening the injector for a precise duration. Code P1268 is triggered when the ECM detects an abnormally low resistance path or an excessive current draw directly between the injector’s power supply circuit and its control circuit for cylinder #8. This indicates an unintended internal short within the injector coil itself, or a direct short between the power and control wires within the injector’s connector or the associated wiring harness. The ECM interprets this as a critical fault that prevents proper electrical activation and deactivation of the injector, leading to incorrect fuel delivery or a complete cessation of fuel injection for cylinder #8. To prevent potential damage to the fuel system, catalyst, or engine, the ECM may disable the injector’s operation entirely or implement a limp-home mode, resulting in a severe engine misfire.

Common Symptoms

• Check Engine Light Illumination: The Malfunction Indicator Lamp (MIL) will be illuminated, often flashing if a severe misfire is detected.
• Engine Misfire: Noticeable rough running, particularly at idle, due to cylinder #8 not firing or firing intermittently.
• Reduced Engine Performance: A significant loss of power and acceleration, especially under load, as the engine is effectively running on fewer cylinders.
• Increased Fuel Consumption: Although one cylinder is not firing, the ECM may attempt to compensate, or an improperly operating injector could leak fuel.
• Rough Idle: The engine will shake and vibrate more than usual due to the imbalance caused by the misfiring cylinder.
• Strong Fuel Odor: Unburnt fuel may be expelled through the exhaust if the injector is shorted in a manner that causes it to leak or constantly spray fuel into the cylinder.

What Causes the Code P1268?

• Faulty Fuel Injector (Cylinder #8): The most common cause is an internal electrical short circuit within the windings or solenoid of the cylinder #8 fuel injector itself. This creates a direct low-resistance path between its power and control terminals.
• Damaged Wiring Harness: A short circuit within the wiring harness leading to the cylinder #8 fuel injector. This can occur if insulation is chafed, melted, or pinched, causing the constant 12V supply wire to short directly to the ECM’s control wire. Rodent damage is also a frequent culprit.
• Corroded Injector Connector: Moisture or contamination ingress into the cylinder #8 injector electrical connector can create a conductive bridge between the terminals, mimicking a short.
• Faulty Engine Control Module (ECM/PCM): While less common, an internal failure within the ECM’s driver circuit responsible for controlling cylinder #8’s fuel injector can sometimes present as a short. This should only be considered after all external components and wiring have been thoroughly tested and ruled out.

How to Diagnose and Troubleshoot

Diagnosing P1268 requires a methodical approach, focusing on the electrical circuit of the cylinder #8 fuel injector.

1. Perform Initial Scan & Freeze Frame Data Analysis: Connect an OBD-II scanner to confirm P1268 and check for any related misfire codes (e.g., P0308). Analyze freeze frame data to understand the engine operating conditions (RPM, load, coolant temp, etc.) when the code was set, which can provide clues.
2. Visual Inspection:
   • With the ignition off, carefully inspect the wiring harness leading to the cylinder #8 fuel injector. Look for signs of chafing, melting, pinching, or rodent damage that could cause a short between wires or to ground.
   • Inspect the fuel injector electrical connector for cylinder #8. Check for corrosion, bent pins, loose connections, or signs of moisture intrusion. Ensure the connector is securely seated.
3. Fuel Injector Resistance Test:
   • Disconnect the electrical connector from the cylinder #8 fuel injector.
   • Using a Digital Multimeter (DMM) set to ohms, measure the resistance across the two terminals of the injector itself.
   • Compare this reading to manufacturer specifications (typically 10-16 ohms for most multi-port fuel injectors). A reading significantly lower (e.g., less than 5 ohms) or near 0 ohms indicates an internal short within the injector coil, confirming it as faulty. An open circuit (OL or infinite resistance) indicates an open winding, which would likely cause a different DTC but is still a fault.
   • Also, check for continuity between each injector terminal and the metal body of the injector. There should be infinite resistance (no continuity) to ground.
4. Wiring Harness Continuity & Short Test (Battery Disconnected):
   • With the ignition off and the battery negative terminal disconnected (for safety and accurate readings), disconnect the cylinder #8 injector connector.
   • Using the DMM set to continuity or ohms, test for a short between the two wires in the harness connector for cylinder #8. There should be infinite resistance (no continuity). If continuity exists, there’s a short in the harness.
   • Test each wire in the cylinder #8 injector harness connector for continuity to chassis ground. Both wires should show infinite resistance (no continuity to ground). If continuity is found on either wire, trace and repair the short to ground.
   • Perform a “wiggle test” on the harness while checking continuity, as shorts can be intermittent.
5. Power and Control Circuit Voltage Check (Key On, Engine Off):
   • Reconnect the battery. With the ignition key in the “ON” position (engine off), carefully use the DMM to check for battery voltage (approx. 12V) on the power supply wire (typically one of the two wires) at the cylinder #8 injector harness connector relative to chassis ground. This confirms the “high side” supply.
   • The other wire in the connector is the control wire from the ECM. With the injector disconnected and the key on, this wire should also typically show close to battery voltage, as the ECM provides a “pull-up” voltage until it grounds the circuit.
   • If there’s no voltage on the power supply wire, troubleshoot the fuse or relay supplying power to the injectors.
6. ECM Driver Test (Noid Light – If No Short Found Externally):
   • If the injector resistance and harness tests pass, reconnect the injector connector.
   • Start the engine. If the misfire is present, use an oscilloscope to monitor the voltage waveform on the ECM’s control wire for cylinder #8. A healthy pattern will show regular pulsed ground signals. An absence of pulses, or erratic pulses, could indicate an ECM driver issue.
   • Alternatively, use a Noid light (a specialized test light that plugs into the injector harness connector). A steady, rhythmic flash indicates the ECM is attempting to pulse the injector. No flash, or a very dim flash, suggests the ECM is not commanding the injector (possibly due to internal failure or shutting down the circuit due to the detected short).

Recommended Repairs and Solutions

Once the diagnostic steps have identified the root cause, the appropriate repair can be made:

• Replace Faulty Fuel Injector (Cylinder #8): If the injector resistance test indicated an internal short, replacing the cylinder #8 fuel injector is the primary solution. Ensure that new O-rings and seals are used during installation to prevent fuel leaks. It is often recommended to replace all injectors as a set, especially on high-mileage vehicles, but for a specific internal electrical short, individual replacement is often sufficient.
• Repair or Replace Damaged Wiring Harness: If the visual inspection or continuity tests revealed a short within the wiring harness, the damaged section must be repaired. This involves carefully cutting out the compromised wire, soldering in a new section of the correct gauge wire, and using heat-shrink tubing for insulation and protection. In cases of extensive damage, replacing the relevant section of the engine wiring harness may be necessary.
• Clean Corroded Connectors: If corrosion was found in the injector connector, thoroughly clean the terminals using an electrical contact cleaner and a small brush. Apply dielectric grease to the terminals before reassembling to prevent future corrosion.
• Replace Engine Control Module (ECM/PCM): Only consider ECM replacement if all other diagnostic steps definitively point to an internal ECM driver failure for cylinder #8. This is a rare and often expensive repair, typically requiring programming or flashing with the vehicle’s specific software. Always ensure external causes have been exhausted before condemning the ECM.

After any repair, clear the DTCs with an OBD-II scanner and perform a comprehensive test drive under various operating conditions to confirm that the P1268 code does not return and that engine performance has been restored.