YourMechanic — San Francisco, CA
Car Repair & Maintenance
Car Won't Start Diagnostic
"Car not starting" is a common complaint among car owners, even in this age of modern efficiency and reliability. There are a number of issues that will make a car hard to start, from the electrical system to the fuel system to the actual starter itself. Finding the root cause of a difficult to start engine can take some investigation.
Common reasons for this to happen:
If the engine cranks, but the car doesn't start:
- Bad fuel pump: A faulty fuel pump won't deliver fuel to the engine, even if you've just filled up.
- Bad spark plugs: Without hot sparks to ignite the fuel charge in each cylinder, there is no combustion and no expansion of the burning mixture. Thus, the engine will not start.
- Bad timing belt: If the timing belt stretches or breaks, the engine will not run. Moreover, continuing to crank the engine may bring the valves into contact with the piston, causing serious engine damage.
- Bad ignition coil: Without a functional coil to step up the voltage, there can be no spark. No spark means no start.
- Faulty cam or crank sensor: If the sensors are faulty they will either provide no information to the ignition system, or will provide incorrect data. Either way, the engine will not fire.
If nothing happens after you turn the key:
- Bad battery or terminals: Batteries have a finite lifespan, and terminals can loosen or corrode.
- Bad starter: This should be obvious from the response to the key. If nothing happens at all when you turn the key, the starter may have reached the end of its life.
- Ignition problem: This could be due to faulty contacts in the ignition switch, or in the wiring.
If there is a grinding noise when you turn the key:
- Starter is bad: Do not persist in cranking the engine.
Please note: If you see a flashing light on the dashboard that says “Security” or “Anti-theft,” then you have an issue with the security or immobilizer system (our mechanics cannot help with the security system).
What does it include?
- Car won't start diagnostic
- 50-point inspection
- Service report
Why is it important?
A non-starting car is an important issue to address. Do not ignore or abandon the car if it’s not starting; this is an issue that should be dealt with promptly. Ignoring a starting issue can further damage the vehicle, which will often result in a more expensive repair. Book a mechanic to perform a thorough inspection as soon as possible.
Additional notes
- Beware of the old roadside dodge of “jumping” the battery from another car. Many manufacturers advise against this practice with new vehicles because of the potential harm that may be done to the car’s electronic system.
- Even if it appears that your car will tolerate a jump from another car, and you happen to have the requisite cables on hand, be sure you know how to do this properly if you don’t have a professional on hand. The attachment sequence and correct polarity selection is crucial, and the procedure can be potentially dangerous.
- Owners of manual transmission cars suffering from a low battery charge might be tempted to bump-start the car – that is, roll the car downhill or get a push until there is enough speed to attempt engaging a gear and releasing the clutch. Unfortunately, modern fuel injection systems require a minimum voltage to initiate fuel injection operation. Without the injectors firing, the car won’t start.
- In the old days, it was recommended to check for fuel delivery by pulling off a fuel line. In today’s cars, with their high-pressure injection fuel rails, this is inadvisable. Cranking until you smell gas at the exhaust tailpipes is a poor idea, too, as it can potently damage the catalytic converter with raw fuel.
Service location
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Recommended will not post to your social networks or spam your contacts.