P1267

What Does Code P1267 Mean?

The diagnostic trouble code (DTC) P1267, “Cylinder #7 High To Low Side Short,” indicates that the Engine Control Module (ECM) or Powertrain Control Module (PCM) has detected an unintended electrical short circuit between the power supply (high side) and the ground control circuit (low side) for the Cylinder #7 fuel injector. In some vehicle manufacturers’ definitions, this code might refer to the ignition coil primary circuit, but it most commonly points to the fuel injector circuit due to the nature of its operation and common failure modes. The ECM/PCM controls the operation of the fuel injector by supplying a constant 12V (high side) and then rapidly switching the ground path (low side) on and off to open and close the injector, delivering fuel to the cylinder. When a P1267 code is set, the ECM/PCM has identified a direct, low-resistance path between the power feed and the ground control wire, bypassing the intended load (the injector solenoid). This prevents the injector from functioning correctly, if at all, and can cause the ECM/PCM’s driver circuit to shut down to protect itself from damage. This electrical anomaly is detected by the ECM/PCM monitoring the voltage drop, current flow, and resistance characteristics of the injector’s circuit, and when these fall outside programmed parameters, the code is triggered.

Common Symptoms

• Check Engine Light (CEL) Illumination: The most direct and common symptom.
• Engine Misfire: Noticeable misfire specifically on Cylinder #7, often accompanied by P0307 (Cylinder 7 Misfire Detected) or P0300 (Random/Multiple Cylinder Misfire Detected) codes.
• Rough Idling: The engine may idle erratically or vibrate excessively due to the absence of combustion in one cylinder.
• Reduced Engine Performance: A noticeable lack of power, poor acceleration, and hesitation, especially under load.
• Decreased Fuel Economy: The ECM/PCM may attempt to compensate for the misfire, leading to inefficient fuel consumption, or the engine may simply be less efficient overall.
• Strong Fuel Odor: If the injector is shorted internally but stuck open, raw fuel could be continually injected into the cylinder, leading to a rich condition and a strong fuel smell from the exhaust. More commonly, a short means the injector does not open at all.
• Engine Stalling: In severe cases, especially during deceleration or at low RPMs, the engine may stall.

What Causes the Code P1267?

• Faulty Fuel Injector #7: The most frequent cause is an internal electrical short circuit within the solenoid winding of the fuel injector itself. This creates a low-resistance path between its internal power and ground terminals.
• Damaged Wiring Harness: The wiring leading to or from Fuel Injector #7 may have insulation that is chafed, melted, or pinched, causing a bare wire to contact either a constant power source, another signal wire, or chassis ground, thus creating a short circuit.
• Corroded Electrical Connector: Excessive corrosion or moisture intrusion within the electrical connector for Fuel Injector #7 can create a conductive bridge between the power and ground terminals, bypassing the injector’s resistance.
• Internal ECM/PCM Fault: While less common, an internal short within the ECM/PCM’s driver circuit for Cylinder #7 could cause this code. This would typically be indicated by persistent failure even after replacing the injector and verifying the wiring, or by multiple injector circuit codes.

How to Diagnose and Troubleshoot

Diagnosing P1267 requires systematic electrical testing and visual inspection. Always begin with safety precautions, including disconnecting the battery before performing resistance checks on isolated circuits.

1. Verify Code and Scan for Others: Use an OBD-II scanner to confirm P1267 is present. Check for any accompanying misfire codes (e.g., P0307) or other injector-related codes. Record freeze frame data for environmental conditions when the code was set. Clear the code and attempt to reproduce the fault during a test drive.
2. Visual Inspection of Wiring and Connector:
   • Locate Fuel Injector #7 and its electrical connector and wiring harness.
   • Carefully inspect the entire length of the wiring leading to the injector for any signs of chafing, pinching, melting, or cuts. Pay close attention to areas where the harness passes near sharp edges, exhaust components, or moving parts.
   • Inspect the electrical connector at Fuel Injector #7. Look for bent or pushed-out pins, corrosion (green or white powdery residue), or signs of heat damage. Ensure the connector is securely seated.
3. Fuel Injector Resistance Test:
   • With the ignition OFF, disconnect the electrical connector from Fuel Injector #7.
   • Using a Digital Multimeter (DMM) set to ohms, measure the resistance across the two terminals of the fuel injector itself (not the harness connector).
   • Compare the reading to manufacturer specifications (typically 10-16 ohms for high-impedance injectors or 2-5 ohms for low-impedance injectors). A reading significantly lower than specified (approaching 0 ohms) indicates an internal short within the injector. An open circuit (OL or infinite resistance) indicates an open winding, which would likely set a different code (e.g., P0207 – Injector Circuit Open).
4. Wiring Harness Short to Ground Test:
   • With the ignition OFF and the injector still disconnected, set the DMM to ohms.
   • Place one DMM lead on each terminal of the injector harness connector, one at a time. Place the other DMM lead on a known good chassis ground point (e.g., engine block).
   • Both terminals should show infinite resistance (OL). If either terminal shows continuity to ground (a low resistance reading), there is a short to ground in the wiring harness.
5. Wiring Harness Short to Power/Voltage Check:
   • Reconnect the battery. With the ignition ON (engine OFF), set the DMM to DC volts.
   • Measure voltage between each terminal of the injector harness connector and a known good chassis ground.
   • One terminal should show battery voltage (this is the constant power feed, or high side). The other terminal (the low side, or ECM-controlled ground) should show near 0V. If the low side shows battery voltage, it could indicate a short to power or an internal ECM fault, though P1267 more specifically points to high-to-low within the component or harness.
6. Wiring Harness High-to-Low Short Test:
   • With the ignition OFF and the injector disconnected, set the DMM to ohms.
   • Measure resistance directly between the two terminals of the injector harness connector.
   • This reading should be infinite resistance (OL). If a very low resistance is measured, there is a short between the high and low side wires within the wiring harness itself.
7. Noid Light Test (Optional):
   • While the engine is cranking (or running if it will), connect a fuel injector noid light to the injector harness connector.
   • A flashing light indicates that the ECM is attempting to pulse the injector. If the light flashes correctly, the ECM’s driver circuit is likely functioning, pointing the fault more strongly towards the injector itself or a direct short in the harness that doesn’t prevent the driver from attempting to operate.

Recommended Repairs and Solutions

Once the source of the short circuit has been identified through systematic diagnosis, the appropriate repair can be performed.

• Replace Faulty Fuel Injector #7: If the resistance test on the injector itself confirms an internal short, replacement is necessary. Always use a high-quality OEM or equivalent aftermarket fuel injector. Ensure proper handling and installation, including replacing O-rings to prevent fuel leaks.
• Repair or Replace Damaged Wiring Harness: If the visual inspection or electrical tests reveal a short in the wiring, the damaged section must be repaired. This involves cutting out the compromised wire, soldering in a new section of the correct gauge wire, and properly insulating the repair with heat-shrink tubing. For extensive damage, replacement of a section or the entire engine wiring harness may be required. Ensure the repaired section is routed away from any potential future chafing or heat sources.
• Clean or Replace Corroded Connector: If corrosion is present in the injector connector, attempt to clean the terminals thoroughly using an electrical contact cleaner and a small brush. If the corrosion is severe, or if the terminals are bent, burned, or compromised, the entire connector housing and its terminals should be replaced.
• ECM/PCM Replacement (Last Resort): Only consider replacing the ECM/PCM after all other potential causes (injector, wiring, connector) have been definitively ruled out through thorough testing. An ECM/PCM replacement typically requires reprogramming or coding to the vehicle, which may require specialized diagnostic tools.

Important Mechanic’s Tips:

• Always disconnect the battery before performing resistance checks to prevent damage to the multimeter or the ECM/PCM.
• When performing resistance checks, ensure the component being tested is completely isolated from the rest of the circuit (unplugged) to avoid misleading readings from parallel circuits.
• Always refer to the vehicle manufacturer’s specific wiring diagrams and component resistance specifications for accurate diagnosis. These can vary significantly between makes and models.
• After completing any repair, clear the DTCs using an OBD-II scanner and perform a comprehensive test drive under various conditions to ensure the code does not return and that engine performance has been restored.
• If symptoms persist after addressing P1267, re-evaluate for other potential issues, such as actual mechanical misfires (low compression), spark issues, or fuel delivery problems affecting other cylinders, as diagnostic codes sometimes overlap or multiple faults can exist.