Engine Stalls While Driving

  When a vehicle stalls while driving it can be similar to an engine that does not start in the morning or after the vehicle has been sitting for a while. As you drive the electrical components heat up and fail by not allowing electrical current to pass through a particular sensor, connection, computer or control module (This will be the same for electric cars as well). Once an electrical connection cools the system will operate again until reheated. One of the first things you will notice is the check engine light will come on, along with the oil pressure and battery warning lights additionally the vehicle will become hard to steer. When this happens pull to the side of the road as soon as possible while the vehicle still has momentum, turn on the emergency flashers, it's important to stay calm. If you are on the freeway in heavy traffic and you are unable to get to the roadside call 911 for assistance, do not leave your car, your safety is the main concern. Steps are arranged in order for popularity and ease.

Let's fix it!

1.  One of the main difference between and engine that will not start and one that stalls while in operation is the ability for the computer to detect the problem. You can easily connect a code scanner which are inexpensive on Amazon (starting at $22.00) and will promptly reveal a signal code or a series of codes which can be looked up here or by searching Google. If a series of codes is displayed start with the lowest number first, this will be the most prudent code while the others may be a result of the engine stalling. Example; P0335, P0442 and P0700, the P0335 code is the lower of the three and is detecting a crankshaft position sensor that is failing.
   
2. Many computers are used simultaneously while using electrical contacts and sensors to operate various systems which can make diagnosing stalling problems tedious, but fear not, CAN scanners (controller area network) are now reasonable (starting at $35.00) on Amazon and will scan the entire car. These computers communicate to each other and can shut down the car if they feel there is a problem. Once this scan has completed any communication or trouble codes will promptly guide you to the problem.
   
3. Engine sensors are subject to heat and one of the most susceptible is the crankshaft sensor. When this sensor goes bad it may or may not set a trouble code so if you have performed a scan and no codes are present suspect this sensor. In most cases replacing the crankshaft sensor can take between 20 and 40 minutes and is a major cause of this problem.
   
4. The fuel pump resides in the fuel tank and is another popular failure. This electrical motor attached to a fluid pump will wear in time causing it to lose fuel pressure intermittently, it can also cause the engine to have low power. To confirm this issue a fuel pressure test is needed at the time the engine is having an issue.
   
5. Most vehicles have a mass air flow sensor (MAF) which measures the volume of air entering the engine at any giving time. This measurement is sent to the vehicles computer in the form of feedback data, the problem occurs when the MAF starts to fail because it will report 0 air flow to the computer which then shuts down the fuel system because it thinks the engine is not running. Luckily most of the time a MAF trouble code will present itself which means the sensor needs to be replaced.
6. If the vehicle battery cables are loose or corroded it can cause a lack of a good connection. Good battery connections are mandatory for the electrical system to stay healthy and operate correctly. This is an easy fix by simply cleaning the battery terminals and cable ends.
   
7. The main computer controls the engine management including fuel pump, fuel injectors and ignition system. Because of the amount of amperage the relay controls it's prone to failure. Locate the relay under the hood in the fuse panel and check for heat from the relay which is a sign it is failing and should be replaced.
   
8. If a fuse or relay connection fails the electrical supply will be severed causing an unstable supply. Mechanics will employ the "wiggle test", with the engine running (idle) wiggle all main fuses and relays to see if the engine stalls, if so remove the fuse or relay and look for signs of heated or melted connections. If found replace the fuse or relay and enhance and clean/replace the connection.
   
9. The ignition switch control the main electrical system which can fail intermittently. This is not too hard to test simply connect a test light to the system feed wire for observation while driving, if the light goes out, the switch is bad. You will need a wiring diagrams for your car which you can obtain by asking one of our technicians or checking Google

Obscure Problems

1. A broken catalytic converter can effectively plug the exhaust system, to check for this condition take a rubber mallet and gently strike the catalytic converter (cold). If it sounds like rocks are inside remove the catalytic converter to inspect for internal damage and replace as necessary.
   
2. The main computer system or PCM (Powertrain control module) controls fuel, ignition, transmission and emission systems and can short out and stop working. This can be reset by shutting the engine off (key off) and allowing the system to sit for about 5 minutes for the system to reboot then try to reset the engine.
   
3. The majority of problems will be electronic based while some problems are obvious such as a loose connector others can be difficult to detect such as an internally shorted wiring harness. To test for this have the engine running an grasp the engine wiring harness under the hood and move it around if the engine stalls you have found the problem. Though rare, it does happen.
   

Questions?

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