Diagnosing a Car That Dies While Driving or While Idling
When Is Your Engine Stalling?
You may experience different symptoms:
- On deceleration, engine rpms may fall below normal idle speed and stall.
- When reaching a stop light, the engine may jerk and die.
- While driving, the engine may suddenly shut off.
Is Your Check Engine Light On?
If your check engine light (CEL) is on, that is your first place to start. Download diagnostic trouble codes from your computer. The codes may point you to the component or system behind the fault.
However, even if you don't see the CEL come on, the following section headings describe the most common circumstances under which an engine may stall, and shows you the most common systems or components where the fault may be located.
If your vehicle dies under particular circumstances, for example only when warmed, when cold, at idle, while moving, or on deceleration, take this into account during your diagnostic. The way your engine fails can give you important clues about the type of trouble the engine is experiencing.
Car Systems That May Cause Stalling
Diagnosing a car that dies while driving or at idle can be difficult. The fault may originate in one or more of several systems:
- Fuel system
- Intake air system
- Charging system
- PCV system
Index: Diagnosing Your Stalling Problem
- A Warning Light Appears on the Dashboard
- My Engine Shuts Off and My Lights Cut off While Driving
- My Engine Dies After a Few Minutes of Operation
- My Engine Shuts Off When I Reach a Stop Light
- My Engine Shuts Off While Idling
- My Engine Shuts Off While Driving, But I Can Restart It Again
- My Car Suddenly Dies
- Getting More Help
1. A Warning Light Appears on the Dashboard
A charging system problem is one of the most common sources of stalling.
Charging systems give some warning when they fail. Usually, you'll see a warning indicator on your dashboard, like a:
- battery light
- voltmeter indicating less than 12 volts
- ammeter showing low current
- charging system warning lamp
- "Service charging system" message
- check engine light
Depending on the particular fault, one or more electrical accessories will not work properly or at all.
The indicator(s) may be warning you that the charging system is not producing sufficient current for your battery and other electrical circuits to operate correctly. Or that a diagnostic trouble code has been stored.
Often, the fault is in the alternator or voltage regulator.
Once your charging system fails, you may be able to drive about 30 minutes, if your battery is in good health. After that, your battery power will be depleted and you'll be unable to restart the engine.
Components to Check:
On some vehicle models, the charging system may be controlled by the car's computer or electronic control unit (ECU). In this case, a charging system problem will trigger a diagnostic trouble code.
This code can be of great help when diagnosing a system problem. If you see the CEL on, download the trouble code(s) using a scanner or code reader. If you don't have a scanner, your local auto parts store may download the codes for you.
However, if the CEL is not on, you still may diagnose the problem. Here are some components that you may want to check:
- Check the battery case for damage.
Check the battery terminals and cables. The most common issue is corrosion around the battery posts and terminals, or a loose cable. Either of these will prevent the charging system from properly charging the battery. Also, the battery may be faulty. So have the battery checked, if necessary.
Check the drive belt. A loose or worn drive belt may fail to properly charge the battery or run the alternator. Check the belt for damage, proper adjustment, and inspect the pulleys for proper alignment.
- Check the charging system circuit, including wires, connectors, fuses, and fusible links.
Have the voltage regulator and alternator checked for proper operation.
2. My Engine Shuts Off and My Lights Cut off While Driving
You may notice that every time you drive over a bump on the road or take a sharp turn, the radio, lights and engine suddenly shut off. This is not only frustrating but a safety issue.
After a few minutes, the engine and the rest of the electrical accessories may start working again.
Although this may seem like a catastrophic problem, the fix can be something simple.
What to check:
- Engage the parking brake, start the engine, and let it idle.
- Pop the hood open.
- Wiggle the battery cables, including the small wire that connects to the car's body, if your vehicle has one.
- If the engine shuts off and the headlights stop working while you do this, you are dealing with a loose, corroded or frayed cable or wire. You'll need to repair or replace the wire, cable or connection.
Other potential problems include:
- A worn out or faulty ignition switch. The headlights will still work.
A blown fuse or fusible link. Your lights and other accessories may still work, but the engine may not restart.
3. My Engine Dies After a Few Minutes of Operation
You start your vehicle and after a few minutes of driving, the engine shuts off. The engine won't start until it cools, just to die again after a few minutes of driving.
Lights, radio and other electrical components will still work.
What to check for:
- faulty ignition coil
- bad ignition module
- faulty crankshaft position sensor
- bad fuel pump motor
Coils and small electronics in ignition modules, motors and ignition coils may develop electrical "opens" that won't show up until the component warms up and wires inside the component expand, causing the open to appear.
To test for an open coil on a magnetic-type crankshaft position (CKP) sensor (with one or two wires) or ignition coil (on single coil models with a distributor):
- Remove the sensor or coil from the vehicle, if necessary.
- Test the sensor resistance; or the primary and secondary ignition coil resistance.
- Compare your results to the specifications in your vehicle repair manual.
- Heat the sensor or ignition coil moderately using a hot air gun or hair dryer.
- Repeat step number 2.
- If the readings differ or the sensor or ignition coil reads infinite resistance, replace the component.
4. My Engine Shuts Off When I Reach a Stop Light
An engine that stalls when you reach a stop light or while idling may point to a faulty idle air control solenoid (IAC). The computer uses the IAC solenoid to bypass the throttle valve and inject more air, depending on engine operating conditions.
A common problem with air passages in the throttle, and the IAC valve itself, is carbon, dirt or fuel varnish buildup. If air can't go through the air ports when needed, the engine may stall when you reach a stop or while the engine is idling.
To check the IAC air passages for clogging:
- Locate the IAC around the throttle body.
- Unplug the IAC solenoid electrical connector.
- Remove the solenoid from the throttle body.
- Check the air passages for carbon buildup and clean them as necessary.
Another possible problem, besides clogging, is that the IAC motor or its circuit may have failed.
If you need to test the IAC:
- Remove the IAC solenoid from the throttle.
- Connect direct battery power to the solenoid using jumper wires.
- If the solenoid doesn't respond, replace it.
The IAC motor can also be checked with an ohmmeter. Consult your vehicle repair manual, if necessary.
Other faults can also trick the computer to operate the IAC solenoid when it should not. For example, a throttle position (TP) sensor that is sending incorrect signals to the computer may cause it to close the IAC solenoid when it shouldn't, stalling the engine. The TP sensor or its circuit may be faulty.
The next video shows a vehicle with this type of problem. Deceleration when coming up to a stop light seems to kill the engine.
5. My Engine Shuts Off While Idling
This condition is similar to the previous one, but the issue here may be more persistent. You may even see the check engine light come on. Different components may cause your engine to shut off at idle.
What to check:
Usually, this points to a vacuum leak, especially on vehicles with a mass air flow (MAF) sensor:
- brake booster
- EGR system or valve stuck open
- PCV valve stuck open
- Intake or throttle gasket
Also, the engine may stall at idle when cold. This may point to a faulty sensor that is sending wrong data to the computer or a system with a worn or faulty component.
What to check:
- Bad fuel pressure regulator
- Bad MAF sensor
- Faulty manifold absolute pressure (MAP) sensor
- Faulty engine coolant temperature (ECT) sensor
- Failed throttle position sensor (TPS)
- Intake vacuum leak
Often, a bad sensor will trigger the check engine light (CEL). Even if you don't see the light on, scan your computer for trouble codes. A pending code may help you focus on a system or component that may be causing trouble.
6. My Engine Shuts Off While Driving But I Can Restart It Again
Here, the engine may stall while the car is moving, and, sometimes, while idling. Often, the vehicle gradually dies. You may feel your car jerk a bit before dying, as if your car has run out of gas. The fault may be in the fuel system.
What to check:
- Clogged fuel filter
Faulty fuel pressure regulator. You can test for fuel pressure yourself using a fuel pressure gauge. Look up the pressure specifications for your particular car make and model in your vehicle repair manual. If you don't have the manual, you can get a relatively inexpensive one from Amazon. Haynes manuals come with step-by-step procedures and illustrations for many troubleshooting, maintenance and component replacement projects you can do at home.
Fuel pump. If you haven't replaced the fuel pump in the last ten years, the pump may be worn and unable to deliver the correct amount of fuel the engine needs above idle speeds. Check the fuel pump if your vehicle stalls when stopping at a red light and then starts right back up.
7. My Car Suddenly Dies
Often, a car may suddenly die on the road or while idling. Unlike the cases discussed above, this failure feels as if the ignition switch was turned off. Headlights and other electrical accessories still work.
Depending on your particular vehicle year and model, the problem can be in the ignition system itself, or a sensor your car computer depends on to keep the ignition system functioning.
What to check:
- Faulty crankshaft position (CKP) sensor
- Problems in the CKP circuit
- Bad ignition switch or circuit
Faulty primary ignition system. Depending on your particular system this may include:
- ignition switch
- ballast resistor
- ignition coil (single coil with a distributor)
- ignition control module
The problem can point to bad contacts in the ignition switch or some other component's electrical connector.
If the fault prevents the engine from restarting, a component, connector or wire has completely failed.
If the problem shows up when the engine warms up and disappears once the engine has cool, check section 3 above, "My Engine Dies After a Few Minutes of Operation."
8. Getting More Help
There are many different reasons that a car might die while driving or at idle. Some reasons depend on your particular model; other times, it is a factory problem.
What to check:
Vehicle manufacturers post technical service bulletins (TSB) that address an issue with a particular system or component in a particular model. And this may include issues for a car that stalls while driving or at idle, for example, a faulty computer program or a defective component used in a particular model.
If you find it difficult to find the source of a particular stalling problem while driving or at idle, check for a possible TSB for your particular model. Search for it online or call your local dealer's service department.
For more help, check this other post that takes a similar approach to diagnosing some specific cases on stalling issues. Also, if your engine stalling problem is accompanied by idle performance issues, this other post on rough idle may help as well.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
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© 2019 Dan Ferrell