How to diagnose a non-starting car


diagnosing a non-starting car

Background

You walk outside to start your car for the morning commute to work. You turn the key to crank the engine and BAM! the car doesn’t start. Your car was running just fine yesterday and now all of a sudden the stupid thing is dead as a doornail. This situation happens to every car owner eventually and your one of the lucky ones if your car happens to pull these antics at your home. I’ve had cars break down on me at work, while I was driving (scary) and once in a McDonalds parking lot. The situation sucks, but if your interested in fixing the car yourself hopefully this article will help you in identifying the source of the problem.

Does the Car Crank?

The first thing you should notice is whether the vehicle cranks or not. If the vehicle does not crank or the crank is weak that means that the starter is not spinning or spinning weakly.

Battery

The first thing you want to check is the battery. Everybody leaves a light on from time to time and the battery may have drained. Alternatively if the car has been sitting for several weeks and you didn’t keep the battery on a trickle charger it may have lost charge.

One way to check the battery is by turning the key two clicks and turning on the windshield wipers. If you notice that they are moving abnormally slow than its almost certainly a battery problem. Your next step will be to remove the battery and take it to an autoparts store like O’Reillys or Autozone and have them test the battery. If the battery comes out good you likely just left a light on and they will charge it for free. If it comes out bad you will have to purchase a new battery.

Remember though that just because the battery is good does not necessarily mean that it’s not a battery related problem. What condition are the battery cable ends in? Sometimes the ends become corroded and stop making a good connection. You can find replacements at your local autoparts store for a few bucks.

Starter

diagnosing a non-starting car - old starter

So your battery tested fine and you want to continue your inspection. If the vehicle does not crank than it could be the starter solenoid or starter motor. On most vehicles the solenoid and the starter motor are attached and sold as one unit. Of course if the starter has gone bad you will need to replace it but the problem is starters often don’t give you a significant warning before they die on you so if you’re stuck somewhere there’s a little trick you can do with a hammer to get the starter running one last time.

First you will need to find the starter. The starter is always going to be between the back of the engine and the transmission because it engages the flywheel to start the car. The big red cable running from the battery also runs down to the starter. If the starter is in a hard to reach position you can use something besides a hammer. When you tap the starter make sure not to tap the electrical connections as the starter has electricity running to it at all times and you could potentially cause a short.

Anti-Theft System

anti-theft system diagnosis

Anti-theft systems are great right? I mean they prevent some schmuck from hot-wiring your car, but what happens when a component of the anti-theft system goes out? Most cars nowadays have keys with chips in them and when you put the key in the ignition it send a signal to an antenna ring that it is the correct key and then the car may be started. Anti-theft systems can be quite a bit more complicated than that, but when a component fails the car will refuse to start.

Some cars have a security light in the instrument cluster. This light comes on when you insert the key and goes off after a short period of time. This means that the anti-theft system recognizes the key. If you turn the ignition and the security light stays on or flashes this means that the anti-theft system either does not recognize the key or there is something wrong with the anti-theft system.

If the key is the problem, the dealership is often the only place that can replace it and you must have documentation proofing that you own the vehicle.

Other Culprits of No-Crank No Starts

Ignition Switch

A bad ignition switch is a common problem especially in older model vehicles. The switch is installed at the back of the ignition lock mechanism. Sometimes you can identify the ignition switch as the culprit simply by jiggling the key in the ignition. If the car then starts it’s likely the ignition switch. A faulty ignition switch often has several other symptoms as well. If the switch fails while the car is running the switch may cut power to the ignition and fuel system and then stall.

Shifter Cable

My friend’s car was once stuck in my undergrad parking lot because her car suddenly would not crank. I inspected it, and discovered that the shifter cable had a plastic grommet that attached it to the shifter. The plastic grommet had broken and the shifter cable had fallen. Once I removed the plastic covering around the steering wheel assembly I simply replaced the plastic grommet with a rubber one and the car started right up!

So What About if the Car Cranks but Doesn’t Start?

An engine requires four things for it to run; fuel, air, spark and compression. If anyone of these four is not delivering than the engine will not run or alternatively it wont run for long. There are several tools that can help you diagnose different crank no start problems and I will go through the diagnosis process.

First Things First… Got Any Check Codes?

Crankshaft position sensors and camshaft position sensors that have gone bad will prevent the vehicle from starting by cutting the spark to the ignition coil. Most of the time these sensors will show a check engine code that is easily identifiable with a scan tool.

If you see that your car has a check engine code check it before you start tinkering with other components.

Engine is Flooded

This is a more common issue on older vehicles. The excess gasoline fouls the spark plugs and washes the oil from the piston rings which lowers the compression. If the engine is not flooded to badly you can press down on the gas pedal while starting the car. This sends a signal to the computer that the engine is flooded and the computer will cut the fuel flow in half.

The foot on the pedal method worked for me when I replaced a fuel pump on my brother’s vehicle and the car would crank but would not start. I tested spark, fuel, air and several other things, everything was fine but the car would not start. Finally I pressed down on the gas pedal while starting the car and it started right up!

Test the Fuel

There are several common problems with fuel delivery that will prevent the vehicle from starting. Namely fuel pump, fuel relay/fuse, fuel pressure regulator, fuel injectors and the fuel filter. The most common no start situations are either a faulty fuel pump or fuse. Even if one or two injectors have become fouled the car will usually start, it will just run like crap. I have yet to see a fuel filter that prevents a vehicle from starting. I have seen fuel filters that are disgusting and make the car run poorly but not to the point where the vehicle will not start.

Check the Fuses

There is usually a Fuel Pump Fuse and a Fuel Pump Relay, check to see if the fuse is blown and what condition the relay is in. If the fuse is blown it’s likely that the fuel pump is also bad but you can confirm this by replacing the fuse and starting the car. Start the car and if the fuse blows again it’s a bad fuel pump.

Fuel Pressure Testing

diagnosing a non-starting car - fuel pressure

Most fuel rails nowadays have a Schrader valve somewhere that you can hook up a fuel pressure tester to. Fuel Pressure Testers can be rented for free from most local auto parts stores. Check to see the applicable fuel pressure on your vehicle and crank the car with the tester attached to the rail. If your getting substantially lower pressure its time to replace the fuel pump.

Spray Test

You can also test if the engine is getting any fuel with some starter fluid. This will likely require that you remove the airbox and the mass air flow meter. Mass air flow meters are very sensitive and you don’t want to douse a $200-$500 sensor in starting fluid. Spray some starter fluid into the intake and try to start the vehicle. If the engine comes alive for a few seconds and then dies than you know you have a fuel problem. If not, you can likely strike fuel from the list and move on to spark or air problems.

Test the Spark

Most cars nowadays have individual ignition coils for each spark plug. For this reason no start spark issues are significantly less common than with older model vehicles that only had one ignition coil. This is because individual ignition coils don’t just all go bad at the same time and a vehicle can run (albeit roughly) with a bad ignition coil.

If you have an individual ignition coil it’s easy to test whether it is operating correctly. Stop by your local autoparts store and buy a spark tester. Then remove the spark plug wire from a spark plug and insert the tester into the wire. Most testers should have a clear cylinder on them to see the spark when the engine starts.

WARNING: Have you ever touched a spark plug wire while the car was running? If you have you’ve likely been zapped before. It’s not a serious shock but its enough to teach you a lesson, the same thing applies to spark plug testers. Set them down on top of the intake before you crank the car. On the otherhand if you ignore my advice and you get shocked at least you know you have spark!

Check to See that Your Getting Air

I rebuilt everything under the intake one time for my baby brother’s 1995 BMW 318i. Once I put everything back together the car would not start of course. It would crank, but that was it. After doing some testing I discovered that his idle control valve refused to open causing the car not to start. I replaced the valve and it worked once again!

Lack of airflow is rarely the cause of a non-starting engine so I’ll run through the possible culprits and tests quickly.

Common airflow problems include bad air filter, idle control valve, mass air flow sensor and of course cracked hoses.

It’s not easy to get an air filter bad enough to prevent a car from starting unless you went mudding or something. It’s so easy to check however you might as well take a look at it.

Idle Control Valve

A bad idle control valve can prevent an engine from starting. The easiest way I have found I can test these is by pressing down on the gas pedal when I start the car. If the car comes to life but then it dies when you let your foot off the gas it’s likely an idle control valve issue. Luckily most are easy to reach, usually they are on top of the intake manifold, somewhere after the mass air flow sensor. However, BMW’s and some other manufacturers place the idle control valve underneath the intake.

Check out this video on BMW Rough Idle Diagnosis:

Mass Air Flow Meter

A bad mass air flow sensor can also cause a crank no-start condition. The sensor will often throw a check engine code when it goes bad but sometimes not. Purchase some mass air flow sensor cleaner from your local auto parts store, remove the sensor, and spray it with the cleaner. DO NOT clean a maf sensor with anything but maf cleaner. They are extremely delicate and you can destroy the sensor with other cleaners. Let the cleaner dry and reinsert the sensor and crank it again.

Cracked Hoses

Cracked hoses rarely will prevent a car from not starting but if you have a really big air leak than there’s a possibility that the vehicle wont start. If the air leak is that big you will be able to hear a loud whooshing sound coming from somewhere around the air intake area. If you can’t locate the faulty area by sight there’s a trick you can use with brake cleaner.

WARNING: Do not spray starting fluid/brake cleaner around the engine when it is hot as this can cause a fire.

Spray the cleaner/started fluid on the air intake hoses until you hear the rpms jump or the engine starts, at that point you’ve found your leak. Alternatively you can also use a smoke machine or a cigarette or a cigar. There are a couple of videos on YouTube of mechanics using cigars to find an air leak, it’s a great method if you don’t mind smoking.

Conclusion

Hope this article helped with your no-start diagnosis. Testing different components is not very complicated but it’s important that you run through the tests mechanically in order to identify the culprit as quickly as possible.

Stephen Metellus

I am a BMW enthusiast and owner of abetterbmw.com! I have been repairing, flipping, and parting out BMWs for nearly ten years. I love these vehicles and I hope you will find my articles and YouTube channel helpful for whatever BMW project you have in store!

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