Owner's Problem Description
The owner of a 1998 Volvo S70 with 60,000 miles reports an intermittent no-start condition. The vehicle runs normally, but the engine suddenly stops while driving or after being turned off. When attempting to restart, the dashboard lights illuminate, but the engine does not crank or make any sound. Occasionally, the car will start after a few minutes of waiting, but this is inconsistent. Previous visits to the mechanic have not resolved the issue, despite having a new Bosch battery installed.
Professional Technical Analysis
This 1998 Volvo S70 is exhibiting a complex intermittent no-start condition, likely related to the ignition system or fuel delivery components. With approximately 60,000 miles on the odometer, the vehicle has a relatively low mileage, but age-related electrical issues can arise. The symptoms describe an engine that unexpectedly stalls and fails to restart immediately, which could indicate a failure in the ignition switch, starter relay, or neutral safety switch (NSS). The absence of any cranking noise suggests that the starter may not be receiving power. It's critical to investigate the state of the ignition switch as it can fail under heat or vibration conditions. Checking for voltage at the starter terminal during the key turn can help identify if the ignition switch is faulty. It's also prudent to examine the NSS for proper operation, as it prevents the starter from engaging if the vehicle is not in 'Park' or 'Neutral'. Additionally, fuel system issues, such as a failing fuel pump or clogged filter, should be considered, especially since the engine cranks but fails to start after the initial stall. The behavior of the vehicle starting intermittently after a wait could suggest thermal issues with components failing when hot.
Possible Causes
Most common causes (ordered by frequency):
- Ignition Switch Failure: The ignition switch may have an internal fault that prevents power from reaching the starter or fuel pump when the key is turned. This is common in older vehicles and can result in intermittent starting issues, especially when heat builds up in the engine compartment. - No cranking sound when the key is turned, electrical accessories may function but no power to starter.
- Neutral Safety Switch (NSS) Malfunction: The NSS may be faulty or misaligned, preventing the starter from engaging when the vehicle is in gear. This can particularly occur if the vehicle is jostled while in 'Park' or 'Neutral'. - No power at the starter terminal when key is in 'start' position, testing NSS shows irregular continuity.
- Starter Relay Failure: The starter relay may be faulty, preventing the flow of electricity to the starter motor. This can often be diagnosed by checking for voltage at the relay terminals when the key is turned to the 'start' position. - No voltage at the relay terminals when attempting to start; relay may click but not engage the starter.
- Fuel Delivery Issues: If the engine cranks but does not start, it may indicate a fuel supply problem. This could be due to a failed fuel pump, clogged fuel filter, or a faulty fuel pressure regulator, leading to inadequate fuel reaching the engine. - Engine cranks but does not start; listen for fuel pump operation when ignition is turned on.
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 - Initial Voltage Check: Start by checking the battery voltage to ensure it is fully charged (12.4V+). Next, test for voltage at the starter terminal when the key is turned to 'start'. If no voltage is present, suspect the ignition switch or NSS.
- STEP 2 - Relay and Switch Testing: Test the starter relay by checking for continuity across the terminals when the key is in 'start' position. If the relay clicks but does not provide power, consider replacing it. Also, check the NSS for proper alignment and continuity.
- STEP 3 - Fuel System Inspection: If the starter engages but the engine does not start, check for fuel pressure at the fuel rail. Using a fuel pressure gauge, ensure the pressure is within specifications (30-40 PSI). If pressure is low, inspect the fuel pump and filter.
- STEP 4 - Thermal Testing: If issues persist, consider thermal testing of the ignition switch and fuel pump. Check if starting issues occur after the vehicle has been running for a while, indicating a heat-related failure in components.
