P1368

What Does Code P1368 Mean?

The OBD-II Diagnostic Trouble Code (DTC) P1368 typically indicates an issue within the Ignition Coil Primary Circuit for a specific cylinder or a general ignition system monitoring circuit, depending on the vehicle manufacturer. While the generic description “Ignition Spare” might suggest a redundant system, in most manufacturer-specific implementations, P1368 points to a fault in a primary circuit associated with a particular ignition coil, often designated by the manufacturer as a specific numerical coil (e.g., Ignition Coil #8 Primary Circuit in some Chrysler/Jeep applications). The Powertrain Control Module (PCM) or Engine Control Module (ECM) continuously monitors the primary ignition circuit for each coil. This monitoring includes checking for proper voltage supply, ground path, and the control signal (square wave pulse) from the PCM itself. When the PCM detects an unexpected voltage or current draw, an open circuit, a short to ground, or a short to voltage in the designated primary ignition circuit that falls outside predetermined operational parameters, it flags P1368. This fault signifies that the PCM is unable to properly control or detect the operational integrity of the “spare” (manufacturer-designated) ignition coil’s primary circuit, which is crucial for generating the high voltage necessary for spark plug firing.

Common Symptoms

• Malfunction Indicator Lamp (MIL) Illumination: The “Check Engine” light will be illuminated on the dashboard.
• Engine Misfire or Rough Idle: If the affected coil is for an active cylinder, symptoms can include noticeable engine misfires, rough idling, vibrations, and poor engine performance.
• Reduced Engine Power or Hesitation: The engine may lack power during acceleration or exhibit hesitation due to inadequate spark delivery.
• Increased Fuel Consumption: Inefficient combustion from a faulty ignition circuit can lead to higher fuel usage.
• Difficulty Starting: In severe cases or if multiple coils are affected, the engine may crank but fail to start.
• Engine Stalling: The engine may stall, especially at lower RPMs or under load.

What Causes the Code P1368?

• Faulty Ignition Coil: An internal defect within the ignition coil itself, such as an open or shorted primary winding, can prevent the coil from drawing the correct current or generating the necessary magnetic field.
• Wiring Harness Issues: Damage to the primary circuit wiring for the affected ignition coil, including open circuits, shorts to ground, shorts to voltage, or high resistance in the wiring.
• Corroded or Loose Electrical Connections: Poor contact at the ignition coil connector, either due to corrosion, loose terminals, or improper seating, can disrupt the primary circuit’s integrity.
• Faulty Powertrain Control Module (PCM)/Engine Control Module (ECM) Driver: A failure within the PCM’s internal ignition coil driver circuit can prevent the module from correctly switching the primary circuit on and off.
• Degraded Spark Plug: While less direct, an excessively worn or fouled spark plug can increase resistance in the secondary circuit, potentially back-feeding or stressing the primary circuit and the coil, leading to premature coil failure.

How to Diagnose and Troubleshoot

Diagnosing P1368 requires a methodical approach using a digital multimeter (DMM), an OBD-II scan tool, and potentially an oscilloscope.

1. Retrieve and Analyze DTCs and Freeze Frame Data: Connect an OBD-II scan tool. Record P1368 and any other present DTCs. Review freeze frame data to understand engine conditions (RPM, load, coolant temp, etc.) when the fault was set. This information can help replicate the conditions during diagnosis.
2. Visual Inspection:
   • Thoroughly inspect the wiring harness leading to the affected ignition coil (consult service manual for specific coil location if “spare” refers to a cylinder). Look for any signs of chafing, cuts, pinches, or burns in the wiring.
   • Examine the ignition coil connector and the coil itself for corrosion, bent or broken pins, proper seating, or signs of arcing.
   • Inspect spark plugs for wear, fouling, or damage, as this can indicate a secondary circuit issue that could overload the primary.
3. Verify Power and Ground at the Ignition Coil Connector:
   • Using a DMM, back-probe the ignition coil connector with the ignition ON (engine OFF). Verify that there is battery voltage (B+) present at the power supply terminal of the coil connector.
   • Confirm good ground continuity at the ground terminal of the connector to the vehicle chassis. High resistance or an open ground will prevent the coil from functioning.
4. Check PCM Control Signal:
   • With the engine cranking or running (if possible), use an oscilloscope to back-probe the control wire (signal wire) from the PCM to the ignition coil. You should observe a distinct square wave pattern, indicating the PCM is attempting to fire the coil. The voltage levels and frequency should be consistent with specifications.
   • If an oscilloscope is unavailable, a noid light or a 12V test light can be used (carefully, ensuring it won’t overload the PCM driver). Connect the test light between the power supply and the control wire. The test light should flash during cranking, indicating the PCM is sending a pulse. A constant ON or OFF indicates a PCM driver issue or an open/short in the control wire.
5. Ignition Coil Resistance Test:
   • With the ignition coil disconnected, use a DMM to measure the primary winding resistance. Compare the reading to manufacturer specifications. An open circuit (OL) or a resistance value significantly outside the specified range indicates an internal coil fault.
   • If accessible and specified by the manufacturer, also check secondary winding resistance (high voltage side).
6. Wiring Continuity and Short Test:
   • Disconnect the PCM connector and the ignition coil connector.
   • Using the DMM, check for continuity of the power supply wire and the control wire between the PCM connector and the ignition coil connector. There should be very low resistance (typically <0.5 ohms).
   • Check for shorts to ground on both the power supply and control wires. There should be infinite resistance.
   • Check for shorts to B+ on the control wire.
7. Swap Test (if applicable): If the code is specific to a single cylinder’s coil and the vehicle has multiple identical coils, swap the suspect coil with a known good one from another cylinder. Clear DTCs and retest. If the code follows the coil to the new cylinder, the coil is faulty.

Recommended Repairs and Solutions

Based on the diagnostic findings, the following repairs are typically recommended:

• Replace the Faulty Ignition Coil: If testing indicates an internal fault with the ignition coil (e.g., incorrect resistance, no spark during a spark test), replacement of the coil is necessary. It is often recommended to replace spark plugs at the same time, especially if they are due for maintenance or if their condition contributed to coil failure.
• Repair or Replace Wiring Harness: If visual inspection or continuity tests reveal damaged, corroded, or open/shorted wiring in the primary circuit, the affected section of the wiring harness should be repaired or replaced. Use appropriate automotive-grade wiring and connectors for repairs.
• Clean or Replace Connectors: If corrosion or poor terminal tension is found at the ignition coil connector, clean the terminals thoroughly or replace the connector housing and terminals as needed to ensure a secure and low-resistance connection.
• Address PCM/ECM Driver Fault: If all wiring, connections, and the ignition coil itself test good, and no control signal is present from the PCM, it points to a faulty ignition coil driver within the PCM. In this scenario, the PCM may require repair by a specialized electronics shop or replacement and reprogramming by a dealership or qualified independent shop. This should always be a last resort after all other possibilities have been exhaustively ruled out.

Mechanics’ Tips:

• Always consult the vehicle-specific service manual for exact wiring diagrams, component locations, and resistance specifications, as “Ignition Spare” can be very manufacturer-specific.
• When replacing coils, use high-quality OEM or reputable aftermarket parts to ensure long-term reliability and proper function.
• After any repair, clear the DTCs and perform a test drive under various operating conditions to confirm the fix and ensure the code does not return.
• Check for any relevant Technical Service Bulletins (TSBs) issued by the vehicle manufacturer for common issues related to ignition coils or P1368 on your specific make and model.