Owner's Problem Description
The owner of a 2005 Mazda 6 reports that there is no spark at the spark plugs, particularly at cylinder one. They have already replaced the ignition coil pack but the issue persists. The owner tested the coil by connecting it to another cylinder that has spark, and it worked. Power was found at the connector for the number one coil, but still no spark is produced. No trouble codes are present. The vehicle is currently inoperable due to this issue.
Professional Technical Analysis
This 2005 Mazda 6 features a 2.3L inline-4 engine with approximately 120,000 miles. The primary symptom is the absence of spark at the number one cylinder, despite the replacement of the ignition coil pack. This suggests a potential issue upstream in the ignition system. Given that the coil works when tested on another cylinder, we can rule out coil failure. The power supply to the ignition coil connector was confirmed, indicating that the power circuit is functioning. The absence of DTCs could imply a failure in the crankshaft position sensor (CKP), which is crucial for spark timing. A CKP sensor malfunction can prevent the PCM from providing the necessary signal to trigger the ignition system. It is also prudent to check the wiring integrity and connector condition, particularly for the CKP sensor. Current vehicle condition indicates no spark at one cylinder, which may lead to further investigation of fuel pressure and compression to rule out additional mechanical issues. It is essential to conduct a thorough diagnostic process, considering the interconnection between the ignition system, PCM, and CKP sensor, as a failure in any of these components can lead to a no-spark condition. Special attention should be given to any visible signs of wear, corrosion, or damage on the connectors and wiring harnesses associated with these components.
Possible Causes
Most common causes (ordered by frequency):
- Crankshaft Position Sensor Failure: The CKP sensor is crucial for generating the signal required for the PCM to initiate ignition. A failure can lead to no spark condition specifically at cylinder one. The CKP sensor should provide a voltage signal between 0.5V to 5V depending on engine speed. If the CKP sensor fails or the wiring to it is compromised, the PCM will not trigger the ignition coils, resulting in a no-spark situation. A visual inspection of the CKP sensor and its connector for any signs of damage or corrosion is recommended. - No spark at cylinder one, confirmed power at the coil connector, no DTCs present suggests potential CKP sensor issue.
- Ignition Control Signal Issue: The PCM controls ignition timing and coil firing based on signals from various sensors, including the CKP sensor. If the PCM itself has faults or if there are communication issues, it may not send appropriate signals to the ignition coils, causing a no-spark condition. Checking the wiring harness and connectors between the PCM and ignition system is essential, along with verifying the PCM functionality. - No spark at cylinder one, confirmed power at the coil connector, no DTCs suggest PCM signal issue.
- Wiring or Connector Issues: Damaged or corroded wiring or connectors can lead to intermittent or complete loss of signal to the ignition coil. Inspect the wiring harness for any signs of wear, breaks, or corrosion, particularly near the connectors. Use a multimeter to check for continuity and resistance in the wiring when the engine is cranking. - Visual inspection of wiring and connectors may reveal signs of wear or corrosion, affecting ignition signal.
Diagnostic Steps
Professional Diagnosis Process
Follow these systematic steps to accurately diagnose the issue. Each step builds on the previous one to ensure accurate diagnosis.
- STEP 1 - OBD-II Scan: Begin by using a professional OBD-II scanner or the GeekOBD APP to check for any stored DTCs or pending codes. Even if no codes are present, the scan can provide valuable freeze frame data. This step is crucial to rule out any other electronic control issues that may contribute to the no-spark condition.
- STEP 2 - CKP Sensor Inspection: Visually inspect the crankshaft position sensor and its wiring for any damage or corrosion. Use a multimeter to check for the CKP sensor output voltage while cranking the engine. The voltage should fluctuate based on engine speed, typically between 0.5V to 5V. If the voltage is out of range, replace the CKP sensor.
- STEP 3 - Wiring and Connector Testing: Check the integrity of the wiring harness and connectors associated with the ignition system. Use a multimeter to measure continuity and resistance. A resistance value above 5 ohms may indicate a fault in the wiring that needs to be addressed.
- STEP 4 - PCM Functionality Check: If no faults are found in the CKP sensor or wiring, verify the PCM’s functionality. This may require professional diagnostic equipment to ensure it is sending the correct signals to the ignition coils. If the PCM is faulty, it will need to be replaced or reprogrammed.
