Troubleshooting / Why Does My Engine Stall?

• Why is my engine running rough?
• Why won't my engine crank over?
• Why does my engine have low power output?
• Why does my engine hesitate?
• How an engine works
• How to check compression
• How to retrieve trouble codes
• How to test engine vacuum
• How to test fuel delivery system
• Engine cranks but wont start
• Engine cranks excessively
• Engine stalls
• Engine vibration
• Engine has excessive smoke
• Rapid ticking sounds when engine is cranked
• Engine has lean mixture codes
• Engine idles high
• Engine idles low
• Engine is making excessive noises
• How to tune up your engine
• How to jump start your engine
• How to change engine oil and filter
• How does a MAF mass air flow sensor work?
• How to test an oxygen sensor
• How does a clutch work?
• How to test a fuel injector
• How to open a car hood

Engine Stalls While Driving

When your car is in use, many electronic components are used simultaneously creating electrical contacts to operate the various systems. Due to the many electrical components that make up these systems, diagnosing a particular one can sometimes be difficult. The malfunction could be from your ignition switch to the fuel pump, but only a certain number of things can cause this condition. An electrical circuit that is starting to fail will do so more when the circuit is warm or hot. Anytime you find signs of heated or melted connections high resistance is present and could cause a shorted connection. Mechanical systems failure can also cause your engine to stall, but the majority of the engine stalling problems will be electronic based. The list below provides instructions for testing the most common problems.

Car Repair Guide Troubleshooting Procedure - READ COMPLETELY BEFORE BEGINNING!

• Step 1 - Anytime you have a problem with electronically controlled components such as an engine, transmission, ABS brake, or SRS (safety restraint system, Air Bag) inspect all fuses using a test light and check the under hood power distribution center and under dash fuse panels. If any signs of heated or melted fuses or fuse holders exist repair or replace as needed. If the fuses test ok continue to the next step. How do I check my car fuses?
   
  
• Step 2 - To check for problems with electronically controlled components such as an engine, transmission, ABS brake, or SRS (safety restraint system, Air Bag) and the fuses test ok a trouble code scan is needed to identify any system trouble. Use a simple scanner tool to retrieve trouble codes and see if any trouble codes gathered relate to the specific problem, like a fuel pump circuit failure code. If a trouble code is present but does not pertain to the immediate problem like an EVAP code ignore it until a later time, after the car is running properly. The reason we repair non-related codes after the engine is running properly is because sometime false codes can be triggered by the engine stalling. Once the engine is running again the code present might cycle and turn itself off. You might say "if the engine stalls shouldn't it have a trouble code?" Sometimes conditions occur that will not be detected by the computer, example: if the air intake boot fails the computer cannot detect the failure, so the engine doesn't idle and the computer thinks everything is ok with no codes. If no trouble codes are present proceed to the next step. How do I scan my service engine soon light?
  
  
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  Check Engine Light Scan for Trouble Codes Video

• Step 3 - Test for proper fuel pressure with a test gauge on the fuel rail or in line somewhere in the system, most throttle body injection cars (TBI) are between 13 psi and 17 psi. and most (DPI) direct port inject systems are between 40 psi and 55 psi. If no or little fuel pressure is present check the fuel pump fuse and fuel pump control relay located in the fuse panel, you can find this fuse and relay by checking your owner's manual, back of the fuse panel cover diagram, or an online auto repair manual, if the fuse or relay has failed, replace it with a new unit and re-test. Have a helper crank over the engine while you place your fingers over the relay, does the relay click under your fingers? If so the relay could be working, there is a chance the relay has burned contacts inside the relay causing the problem but we will get back to that. Next, access the fuel pump power feed wire, there are a few ways to do this. First you need a wiring schematic to find the color wire needed for testing, every manufacturer has a different color wire so the best way to do this is with an online auto repair manual. Once you have found the color wire it should be located in the wiring harness near the fuel tank which is where the pump is located. Ground the test light and probe (pierce the wire's outer coating with the test light probe point) the wire, have a helper crank the engine over. If the test light illuminates and you have no fuel pressure the fuel pump had failed and needs to be replaced.  If the test light doesn't illuminate the fuel pump control relay has probably failed, replace it with a new unit and re-test, in most cases this relay is under thirty dollars. There is an outside chance the power feed to the relay has failed but it doesn't happen very often. If this is the case use an online auto repair manual to trace the power source to the relay. If good fuel pressure is present continue to next step. How do I check my fuel pressure?
   
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  Fuel Injection Pressure and Pressure Regulator Test

  
  
  
• Step 4 - The ignition system in your car ignites the fuel inside the engine's combustion chamber at the optimal time in the piston stroke to produce the most power while emitting the least amount of emissions as possible. There are many configurations of ignition systems but all operate on the same principle, create a low energy field and collapse it onto a high energy coil that transfers the electrical energy into the secondary ignition system, which consists of the coil wire, distributor cap and rotor (if equipped) plug wires and finally the spark plug. This system is triggered by the primary ignition system, this system varies depending on manufacturer but all operate on the same principle by using some kind of low voltage trigger system such as a crankshaft position sensor (CKP) or camshaft position sensor (CAS). This low voltage system (1.5 to 3.0 volts) is amplified to 12 volts by using an ignition module (amplifier) and then transferred to the primary side of the ignition coil. The ECM (engine control module) controls the engine ignition timing by advancing and retarding the primary trigger signal. In older cars, points and condenser with a vacuum advance unit performed this job. We have listed the most common causes for an ignition system to fail or misfire, visit -  How to test the engine ignition system?
   
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  Basic Ignition System Test

• Step 5 - The main PCM power relay carries high amperage and is prone to failure, especially when it is in use for a while and gets hot. If the PCM relay fails it will shut down the engine management system and stall the engine. If you suspect the relay could be failing remove the relay cover and inspect the relay contacts. If the relay contacts look burned and have an ash look to them the relay needs to be replaced. If the relay checks ok proceed to next step. How to check a car relay?
   
• Step 6 - The battery connection in your car can be loose and vibrating when the car running. This vibration causes the battery terminal to short very rapidly creating an electrical system surge that can cause the engine to stall. The battery cable connection must be clean (free from corrosion) and tightly fastened to allow the flow of electricity from the battery to the starter. With the key in the off position located battery to inspect the battery cable connections. Battery cable connections must be tight and not wiggle on the battery terminal. If the cable is lose remove it and clean, then tighten the cable with a wrench or socket wrench. Use baking soda to neutralize any suspected acid residue before work begins. How do I check my battery connections?
   
• Step 7 - The exhaust system on your car is designed to move exhaust gasses created by the engine to the rear of the car. In this exhaust system is comprised of many parts, among these parts are a muffler and catalytic converter. Either of these parts can break apart internally and cause a temporary blockage of the exhaust system causing the engine to stall. To check for this condition start with the engine cold, then take a rubber mallet and hit the muffler and catalytic converter. There should be very little rattling sound when struck with the hammer. If you can hear what sound like rocks inside your exhaust system, remove it and inspect it for internal damage.

  
  Plugged Catalytic Converter from Broken Catalyst Material
   

• Step 8 - The ignition switch or control relay in your car is the main electrical system connection for the starter, ignition, computer and accessory systems. This switch is constructed with metal connects that transfer electrical power when the switch is engaged. If these contacts become corroded or overheated they can short circuit causing these systems to fail and the engine to stall. To check for this condition you will need an online auto repair manual to identify the ignition power wires. To gain access to your ignition switch power feed wires locate the ignition switch, some cars it is about half way down and on top of the column and others the ignition switch is under the plastic cover around at the top half of the column. Ground a test light and insert the probe into the main power output wire. Next, securely mount the test light (tape works best) while the test light probe is inserted into the main power output wire in a position where it can be observed easily while driving. When the car is in operation the test light will be illuminated, if the light goes out while driving the ignition switch is bad and needs to be replaced. There is a slim chance the power feed wire is failing but it doesn't happen very often. If you have replaced the ignition switch and the test light still goes out the main power feed wire to the ignition switch is shorting. Use a repair manual to trace to power feed wires and repair as needed and then recheck the system.
   
  
• Step 9 - There are a variety of sensors that help the engine management computer control the fuel, ignition and emission systems. If any one of these sensors short circuits it can cause the computer to shut down, the sensors most prone to failure deal with extreme heat like the oxygen and coolant sensor. You might say "if the sensor is shorted wouldn't it cause the service engine soon light to illuminate?" and the answer is not always yes. The problem is if the sensor shorts in extreme heat conditions it can causes the computer to shut down, stalling the engine. The computer is programmed to trigger a "service engine soon light" when the sensor fails for a prescribed amount of time, say three minutes, it only takes a sensor one second to stop the computer system. When the sensor cools it stops allowing the engine to restart. If you think this problem is happening to you, temporally disconnect major sensors one at a time and retest. (This will cause a service engine soon light so the engine codes will need to be cleared after testing is complete)
   
  
• Step 10 - The main computer system or PCM (Powertrain control module) in your car operates the engine, fuel, ignition, transmission and emission systems. The PCM consists of electronics which are mounted on multi-layer circuit board which monitors and adjusts the air/fuel mixture and utilizes a catalytic converter to minimize amount of pollution produced from the engine. The PCM operations in two separate modes, closed loop, which means the computer has completely taking over the operation system. And open loop which is used when the engine is cold and operates on a preset program. The engine must be at operating temperature before it can go into closed loop. Think of the PCM as a small designated computer with a programmed operating system much like an Xbox or PS2. As the PCM heats up it can cause electrical connection inside to short and stop the PCM from working causing the engine to stall. There is no easy way to determine if the PCM is failing, if you suspect the PCM replace it with a new or used unit and recheck.

For exact specific repair procedures for any of the steps above visit our online repair manual page.

WARNING! Always have the vehicle under inspection on level ground, in park with the emergency brake on. Always wear protective eyewear, gloves and necessary clothing before inspection or work begins. Never crank an engine over when anyone is near the battery or engine. Always have an operational fire extinguisher close by, obey all first aid instructions in the event of an injury. Never stand in front or behind a vehicle when starting or running. When engine is cranked over keep hands and clothing away from rotating components. Anyone with a heart pacemaker should not perform this test.

Additional Resources

• Why does my engine overheat?

Check Manufacturer Specific Engine Stalling Question Questions and Answers

Related Subjects

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• How emission controls work?
• How an ignition system works?
• Engine won't crank questions?
• How performance exhaust works?

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