Dan Ferrell scrive di manutenzione e riparazione auto fai-da-te. Ha certificazioni in tecnologia di automazione e controllo.
1. Batteria scarica
2. Motorino di avviamento o sistema difettoso
3. Alternatore difettoso
4. Filtro del carburante intasato
5. Regolatore di pressione del carburante difettoso
6. Pompa del carburante difettosa
7. Bobina o modulo di accensione difettoso
8. Sensore di posizione dell'albero motore o sensore di posizione dell'albero a camme difettoso
9. Perdita di vuoto importante
10. Cinghia di distribuzione guasta
Più avanti in questo articolo, ti aiuteremo a navigare attraverso alcuni test e decidere quale problema è tuo in modo da poter tornare in strada.
Il tuo problema molto spesso rientra in una di queste cinque categorie:
Quando si ha a che fare con un motore che si rifiuta di avviarsi, è possibile utilizzare i suoni, o la loro mancanza, come strumento diagnostico. I suoni ti aiutano a concentrarti sul sistema o sui sistemi in cui potrebbe essere localizzato il problema, eliminando altri potenziali punti problematici.
Se si sente un singolo clic solido quando si tenta di avviare l'auto, il problema potrebbe essere localizzato nel motorino di avviamento o nel circuito.
Un tintinnio proveniente da sotto il cofano quando si tenta di avviare il motore potrebbe indicare una batteria scarica, terminali della batteria allentati o corrosi o un problema con l'alternatore o il sistema di ricarica.
Se non senti nulla quando tenti di avviare l'auto, controlla:
Quando giri la chiave di accensione per accendere il motore, potresti sentire il solito rombo del motore, ma il motore non si avvia mai. Se sì:
Se necessario, consulta le Risorse sezione in fondo a questo post per assistenza su questi e altri problemi.
Spesso, una condizione di mancato avviamento può essere ricondotta a un guasto nel sistema di alimentazione. Se il tuo motore gira ma si rifiuta di avviarsi, esegui questo semplice test. Questo test può dirti se il problema è correlato all'erogazione di carburante.
Se il motore si avvia per un paio di secondi e poi si spegne, molto probabilmente il tuo problema è legato al carburante. Controllare il filtro del carburante, il regolatore di pressione del carburante e la pompa del carburante, come indicato nelle sezioni seguenti.
Il video seguente mostra come utilizzare il liquido di avviamento.
Ora che hai un'idea di quale sistema deve essere indagato, puoi iniziare a indagare. Le prossime dieci sezioni trattano i dieci guasti più comuni che potresti dover affrontare quando la tua auto si rifiuta di avviarsi e come procedere per controllare ogni potenziale guasto.
Questo è uno dei motivi più comuni per cui un'auto non si avvia. Una batteria per auto può durare fino a sei anni, a seconda della manutenzione e delle condizioni operative. Condizioni meteorologiche estreme, ad esempio, ne ridurranno la durata.
Tuttavia, non è raro che una batteria perda improvvisamente la carica.
Controllare i collegamenti dei terminali della batteria. Rimuovere la corrosione e assicurarsi che i terminali siano ben stretti. Quindi controlla il livello dell'elettrolito, se la batteria ha i tappi rimovibili.
Quando la tua auto si rifiuta di avviarsi, assicurati che la batteria sia carica. Puoi utilizzare un multimetro digitale (DMM) per verificarne lo stato di carica.
Per controllare lo stato di carica della batteria:
Se è necessario ricaricare la batteria, utilizzare una carica lenta, se possibile. Ciò contribuirà a ripristinare le condizioni della batteria.
Il tuo negozio di ricambi auto locale può verificare se la batteria è ancora buona.
Il motorino di avviamento e il suo circuito sono altre comuni fonti di problemi. Questo sistema potrebbe essere il colpevole se si sente un clic solido quando si tenta di avviare il motore.
Potrebbe esserci un problema con il solenoide di avviamento, il relè o il motorino di avviamento. Se necessario, controllare il circuito con un test di caduta di tensione. Consulta le Risorse sezione in fondo a questo post per assistenza con questo test.
Also, your local auto parts store will check the starter motor for free, but you'll need to remove the starter from the vehicle.
Along with a dead or bad battery, alternator issues are one of the most common reasons for a no-start condition.
Usually, the charging system will turn on a warning light on the dashboard alerting you about a fault in the system. However, there are many reasons a charging system may fail to deliver a charge to the battery or electrical power to other systems in the vehicle.
Points to check:
Keep in mind that a corroded battery terminal could be a sign of an alternator overcharging the battery.
If you don't want to do it, your local auto parts store will check the alternator for you.
Most manufacturers recommend replacing the fuel filter every one or two years. Replace your fuel filter as recommended.
Although many fuel filters include a bypass valve in case the filter clogs, not all come equipped with this valve. Besides, rust and other sediments in the fuel tank can make their way to the fuel filter and clog its filter element.
Before giving out completely, a clogging fuel filter will give you one or more signs. For example, you may notice a lack of engine power at high speeds, difficulty starting the engine, or poor acceleration.
Check your repair manual to inspect the fuel filter and system in your particular model, if necessary.
If you suspect insufficient fuel reaching the injectors, do the quick fuel system delivery check as described in the second section of this post.
A fuel pressure regulator (FPR) limits the amount of pressure buildup in the system, typically to between 35 and 45 psi. Check your vehicle repair manual for your model specifications.
But FPRs can fail. If the internal diaphragm begins to leak fuel into the intake manifold, pressure will drop, and the cylinders will be flooded with fuel, making the engine hard to start.
Also, if too much raw fuel reaches the catalytic converter, the Check Engine Light (CEL) will begin to flash on your dashboard.
If you suspect insufficient fuel reaching the injectors, do the quick fuel system delivery check as described in the "Pre-Diagnostic 2" section of this article above.
You can perform a few FPR tests at home. See the Resources section at the bottom of this article for some help.
Fuel pumps have a long service life. They can last 80,000 miles or more. If your fuel filter and fuel pressure regulator are fine, but you have a fuel issue, probably your fuel pump is bad.
When turning the ignition key to the "On" position, before trying to start the engine, you should hear a buzzing sound for a couple of seconds. This is the sound of the fuel pump motor being activated to prime the fuel delivery system.
If you don't hear this sound, it may be that:
To verify a fuel delivery issue, do the quick fuel system delivery check as described in the second diagnostic section near the top of this article.
Also, check the repair manual for your particular model to see how to test the fuel pump, if necessary.
For the most part, ignition coils or modules are pretty reliable. Unlike spark plugs, wires, and distributor caps (depending on the model), an ignition coil or module doesn't require much attention.
However, they can fail from time to time. The conditions under which they operate, like heat, vibration and other engine performance issues, can have an adverse effect on any of these components after many miles of operation.
Older vehicle models used a single ignition coil and module to deliver a spark to the spark plugs. Newer models may use a module and one coil per spark plug. A failed coil or module in one of these models will certainly prevent the engine from starting.
You can use a spark tester to verify the presence and condition of the spark. You can buy one at your local auto parts store. If possible, get an adjustable spark tester you can use in different vehicles.
The Resources section at the bottom of this post, and your vehicle repair manual, can help you check an ignition coil or test for the presence of a spark in the ignition system.
The crankshaft position (CKP) sensor monitors engine speed, and the camshaft position (CMP) sensor tracks the position of the camshaft.
The electronic control module (ECM), the car's computer, uses the signal from both sensors to control fuel injection operation, direct ignition, and, depending on vehicle model, the variable valve timing system.
If any of these sensors fails, your car may fail to start.
Sometimes, depending on the specific fault, a bad CKP or CMP will trigger the check engine light (CEL). Whether the CEL illuminates on your dashboard or not, it's a good idea to scan the computer memory for potential diagnostic trouble codes (DTCs) that can help you diagnose a no-start condition.
If you don't have a scan tool, your local auto parts store may download DTCs for you without cost.
Also, check your vehicle repair manual. And, within the Resources section at the bottom of this post, you'll find links to other posts to help you check these sensors yourself, if possible.
Major vacuum leaks are not common, but they definitely happen. A vacuum leak can make the air-fuel mixture too lean, preventing the engine from starting.
A leak may come from a vacuum line, intake manifold gasket, throttle body gasket, leaking EGR valve gasket, power brake booster or positive crankcase ventilation (PCV) valve.
Vacuum leaks can be tricky to find. You can visually inspect every vacuum hose and trace it with your hand, feeling for tears or damaged spots. Also, pay attention to hissing sounds that may indicate a leak.
A leaking gasket is harder to detect, though, unless you have a smoke machine designed for this purpose.
Se necessario, consulta il manuale di riparazione del tuo veicolo.
You won't see this type of failure often. Timing belts can last between 50,000 and 100,000 miles or more, depending on your particular model. And if you have a timing chain rather than a belt, you may never have to worry about replacing it.
Still, if you've checked the usual suspect without success, check for a failed timing belt or chain.
The engine's crankshaft and camshaft are joined by a timing belt or chain through a series of sprockets. When this belt or chain brakes or wears out, or the tensioner fails, the crankshaft won't be able to rotate the camshaft anymore, making it impossible to start the engine.
Checking for a failed timing belt or chain:
On a vehicle fitted with a distributor, you can remove the distributor cap and try to fire up the engine. If the distributor rotor doesn't move, most likely your timing belt or chain, or one of the system components, has failed.
On models with multiport fuel injection systems, sometimes it's possible to remove the timing belt or chain cover to check for camshaft movement while trying to start the engine. Or you may be able to remove the oil cap from the valve cover, or the cover itself if necessary, to check for valve movement while trying to start the engine. If there's no movement, it's time to check the belt, chain, or system components.
If the camshaft rotates, you may still want to verify ignition timing. If the belt or chain has skipped some sprocket teeth, it may be difficult or impossible to start your engine.
Consult your vehicle repair manual to check crankshaft and camshaft synchronization.
Of course, there are other model-specific components or systems that can prevent your vehicle from starting. Ad esempio:
Consult the repair manual for your specific make and model for help on these and other systems or components.
To sum up, when your car won't start, begin your diagnostic with the most simple components or obvious potential problems, as in Diagnostics 1 and 2 at the beginning of the article:
Then you can start checking the alternator, starter motor, ignition, fuel system pressure, and their circuits.
Most of the time you'll be able to fix the problem yourself. Sometimes, you will need to replace a fuel pressure regulator, ignition coil, module, or fuel pump, or fix a vacuum leak.
See the Resources below for diagnostic ideas if you have narrowed your problem down to a particular system.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional. 
Ecco dieci motivi per cui la tua auto non si avvia ...
...In cinque categorie generali
Alcuni consigli prima di iniziare la diagnostica
Pre-diagnostica 1:utilizzo del suono come strumento diagnostico
Che suono senti quando provi ad avviare il motore?
Pre-diagnostica 2:un controllo rapido dell'erogazione del sistema di alimentazione
Ora:i dieci errori comuni e come verificarne ciascuno
1. La batteria è scarica
2. Motore o sistema di avviamento difettoso
3. Faulty Alternator
4. Fuel Filter Clogged
5. Faulty Fuel Pressure Regulator
6. Bad Fuel Pump
7. Faulty Ignition Coil or Module
8. Faulty Crankshaft or Camshaft Position Sensor
9. Major Vacuum Leak
10. Failed Timing Belt
A Few Unusual Additional Possibilities
Dealing With a Car That Won't Start
Resources on Starting System Faults
Car starter problems? Don't blame the starter motor yet. These 5 troubleshooting tips will help you find the culprit.
Testing the voltage drop can help you find trouble spots in your starter circuit before you swap components unnecessarily.Resources on Charging Circuit Faults
Diagnose alternator and charging system problems with this practical guide to get your car back on the road faster.
Voltage-drop test your charging system circuit before condemning your alternator.Resources on the Fuel System
Learn how to test a fuel pressure regulator to save money and time in car repairs.Resources for Dealing with the Crankshaft and Camshaft Sensors
Troubleshoot an inductive or Hall effect type crankshaft position (CKP) sensor using a digital multimeter.
You can do a camshaft position sensor test using a digital multimeter at home and, if necessary, using a few common tools.
If your car’s ignition system has no spark, a few simple tests can help you locate the fault.Resources for Dealing With Battery Faults
This guide will show you how to use a digital multimeter, hydrometer, and other simple tools to troubleshoot, inspect, and clean your battery if necessary.
Find that parasitic battery drain that's causing your car battery problems whether you have a newer or older vehicle model.
