Owner's Problem Description
The owner of a 2002 Mazda Protege5 reports intermittent starting issues. The vehicle sometimes makes an attempt to start when the key is turned, but it fails to start completely. This problem occurs unpredictably, not consistently after periods of idling or running. The owner has noticed that the vehicle will start after a few hours or a day, but cannot identify a specific trigger. Previous repairs include a tune-up related to a P0300 code, but no diagnostic codes have been consistent with the current starting issue.
Professional Technical Analysis
This 2002 Mazda Protege5, equipped with a 2.0L I4 engine and approximately 150,000 miles, is exhibiting intermittent starting issues. The owner describes the vehicle sometimes cranking but failing to start without a consistent pattern. Possible environmental factors include temperature fluctuations, which can exacerbate issues related to electrical connections or component failures. The vehicle has previously shown a P0300 code, indicating a random misfire detected by the PCM. These misfires can be caused by various factors, including ignition system faults (spark plugs, coils, or wires) or fuel delivery issues. Given the intermittent nature of the problem, it's crucial to analyze the vehicle's electrical and fuel systems thoroughly. System interconnection reveals that a faulty ignition control module (ICM) or fuel pump relay could be causing the PCM to receive inconsistent signals, leading to starting failures. Additionally, the coolant temperature sensor may impact fuel mixture adjustments, contributing to starting difficulties. Current vehicle diagnostics should focus on retrieving stored fault codes and observing live data parameters to identify any discrepancies in the ignition timing or fuel pressure. A thorough inspection of battery voltage under load (should be 12.4-12.8V), grounds, and connections, alongside a fuel pressure test (should maintain 30-40 PSI) is recommended to assess the condition of the starting system and fuel delivery components. Safety concerns include ensuring the vehicle can start reliably to avoid potential hazards during operation.
Possible Causes
Most common causes (ordered by frequency):
- Intermittent Ignition Control Module (ICM) failure: The ICM may experience thermal breakdown, leading to inconsistent spark generation. This is common in older Mazda vehicles and can cause the engine to crank without starting. The ICM should be tested for proper voltage output during cranking (should be around 10-12V at the ignition coil). - Check engine light activation, intermittent cranking without starting, potential stored codes related to ignition issues.
- Fuel Pump Relay Failure: The fuel pump relay may be faulty, causing intermittent power supply to the fuel pump. This can lead to inconsistent fuel delivery, preventing the engine from starting. Relay should be tested for continuity and voltage drop when energized (should be less than 0.5V). - Intermittent starting, buzzing sound from the fuel tank, absence of fuel pressure when starting fails.
- Coolant Temperature Sensor malfunction: A faulty coolant temperature sensor may send incorrect temperature readings to the PCM, affecting fuel mixture adjustments. This can lead to hard starting when the engine is cold or hot. The sensor should read approximately 0.5V at cold (below 75°F) and 4.5V at operating temperature (around 195°F). - Poor cold start performance, potential stored codes related to temperature sensor, engine running issues.
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: Start with a detailed scan using an OBD-II scanner or GeekOBD APP to retrieve any stored fault codes. Pay close attention to misfire codes and any pending codes that may indicate intermittent issues. Freeze frame data can provide valuable context about the vehicle's operating conditions at the time of the fault.
- STEP 2 - Live Data Monitoring: Utilize the GeekOBD APP to monitor critical parameters such as fuel pressure, ignition timing, and coolant temperature. Check fuel pressure at the fuel rail; it should be between 30-40 PSI during cranking. Observe the coolant temperature sensor readings to ensure they are within expected ranges. Document any discrepancies during starting attempts.
- STEP 3 - Component Testing: Test the ignition control module and fuel pump relay. Check the ICM voltage output while cranking (should be 10-12V). Test the fuel pump relay for continuity and voltage drop (less than 0.5V). If either component fails, replace with OEM or quality aftermarket parts.
- STEP 4 - Road Test: Conduct a controlled road test while monitoring live data through the GeekOBD APP. Document any parameter deviations during starting attempts, paying particular attention to fuel delivery and ignition timing. This will help isolate the cause of the intermittent starting issue.
