Intermittent no-starts are the most frustrating to diagnose because the problem disappears at the shop. The pattern usually points to a heat-sensitive component, a worn switch with intermittent contact, or a wiring issue that moves with temperature. Top suspects: a failing crankshaft position sensor, a worn ignition switch, a marginal starter, a flaky neutral safety switch, or corroded battery cables.
Intermittent no-start always gets worse. Document when it fails (cold? hot? after a drive?) - the pattern is your biggest diagnostic clue. Heat-related = sensor or starter. Random = ignition switch or cables.
Each cause is rated by likelihood, repair cost range, DIY difficulty, and severity. Start with the highest-probability cause and work down.
The classic heat-soak failure. Sensor works cold, fails when hot, recovers when cool. If your car will not start after a 20-minute drive but starts fine the next morning, this is the #1 suspect.
Internal contacts get pitted and intermittent. Sometimes the key works, sometimes you have to jiggle it. Usually accompanied by dash flicker at the START position.
If wiggling the shifter back to Park or shifting to Neutral makes the car start, the range switch contacts are worn. Common on 100k+ mile automatics. Replacement is $50-250.
A dying starter will sometimes engage, sometimes click, sometimes do nothing. If you can hear a difference each time you turn the key, the brushes or solenoid contacts are intermittent.
The cable looks fine outside but is green and crumbly inside the insulation. Resistance changes with temperature and movement, giving you random no-starts. Replace both battery cables.
If the engine cranks but does not start (versus no-crank), a heat-sensitive fuel pump relay is a top suspect. Swap with an identical relay in the fuse box as a test.
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If your scan tool is showing one of these codes alongside this symptom, that is your starting point. Click any code for the full diagnosis.
Intermittent no-start almost always means a worn electrical contact (ignition switch, neutral safety, starter) or a heat-sensitive sensor (crankshaft position sensor is the classic). Track when it fails - the pattern points straight to the cause.
Catch it when it happens. Try to start the car cold versus hot. Log conditions. Bring those notes to the shop. If the car will not fail in their bay, ask them to run a key cycle test and check live data on the crankshaft sensor and fuel pump relay.
Not yet. Test the battery and cables first ($0 free test). Then check the ignition switch and neutral safety. The starter is third on the list because it is the most expensive guess.
Yes on push-button-start vehicles. A weak fob battery means the car only sometimes recognizes the fob. Replace the CR2032 ($3) before chasing anything else.
Intermittent today, stranded next week or next month - it always gets worse. Treat it as urgent. Carry a portable jump starter ($60-100) until you fix it.
Crankshaft sensor: $100-250 installed. Ignition switch: $80-300. Neutral safety switch: $50-250. Starter: $200-500. Battery cables: $20-150. Battery: $100-250.