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Why Does My Car Stall While Driving?

Dan Ferrell writes about do-it-yourself car maintenance and repair. He has certifications in automation and control technology.

A car may stall on you without warning while you are driving.

A car may stall on you without warning while you are driving.

When your car stalls while driving, trying to find the cause behind the fault can be hard at times. The culprit can be a faulty:

  • Fuel filter
  • Throttle position sensor
  • MAF sensor
  • Fuel pump
  • Ignition coil
  • Catalytic converter

or a number of other sensors or faulty conditions in a system. Often, a bad sensor will trigger a diagnostic trouble code. But even then, you still need to test the potential bad sensor, because problems in other areas can often cause a particular sensor to report incorrect data to the computer.

Whether or not you have found a diagnostic trouble code (DTC), take a look at this list to help you diagnose the problem. Most components described in the following sections link to diagnostic or troubleshooting procedures you can do at home using, in most cases, common tools.

If you plan to do your own diagnostic procedure, it's a good idea to have the repair manual for your particular vehicle make and model.

If you don't have the manual yet, you can buy a relatively inexpensive copy from Amazon. Haynes manuals come with step-by-step procedures for many maintenance, troubleshooting and replacement tasks you can do at home. So you'll recoup your investment in a short time.

Index

1. Fuel Filter

2. Fuel Pressure Regulator (FPR)

3. Catalytic Converter

4. Windings and Coils

5. Idle Air Control (IAC) Valve

6. Mass Airflow (MAF) Sensor

7. Exhaust Gas Recirculation (EGR) Valve

8. Vacuum Leaks

9. Manifold Absolute Pressure (MAP) Sensor

10. Throttle Position Sensor (TPS)

11. Engine Coolant Temperature (ECT) Sensor

A restricted fuel filter can cause your vehicle to stall.

A restricted fuel filter can cause your vehicle to stall.

1. Fuel Filter

Over time, the fuel filter becomes restricted with debris and begins to hamper fuel flow. If not serviced, the clogging filter will drastically reduce fuel volume. At first, you may see the effects under load, when driving uphill for example, or at highway speeds when more fuel is demanded by the engine and the car performs poorly.

Soon after, the engine may begin to suffer random misfires or stall. Check your car's manufacturer schedule and, if necessary, replace the fuel filter.

Unfortunately, many newer vehicle models come with an in-tank fuel filter. Although their service life may last up to 100,000 miles, sometimes it is necessary to replace them before. So make sure the fuel filter is causing the problem or has reached the end of its service life. When necessary, do a fuel volume test.

Another indication that you may be dealing with this issue is a check engine light with a DTC indicating a lean fuel problem. A clogged fuel filter may have triggered the code, but the trouble code may point to a particular sensor. That's why it's important to test any apparent faulty sensors indicated by the computer before replacing them.

To replace the fuel filter, you may need to lower the fuel tank, and, in some models, replace the fuel module or assembly along with the fuel filter, depending on your particular model.

Check your car owner's manual or vehicle repair manual.

Fuel system problems may also lead to stalling problems.

Fuel system problems may also lead to stalling problems.

2. Fuel Pressure Regulator (FPR)

A bad fuel pressure regulator can also cause a stalling problem while driving. A torn FPR diaphragm is a common fault in bad FPRs.

In most cases, you can just disconnect the vacuum hose from the regulator to do a quick check. The presence of fuel or fuel odor in the vacuum hose will point to a leaking FPR.

You can also check the fuel pressure regulator at home using a few simple tests.

3. Catalytic Converter

Catalytic converters are pretty reliable. But engine performance problems can have an adverse effect on them.

Misfires, for example, will cause the catalytic converter to overheat and, eventually, clog. A plugged converter will restrict exhaust flow. When this happens, the engine may run fine for a few minutes before stalling because of exhaust pressure buildup.

You can use a vacuum gauge to test the catalytic converter, or a pressure gauge.

  1. Set the emergency brake and set the transmission to Park (automatic) or Neutral (manual).
  2. Remove the oxygen sensor from the exhaust manifold and install the pressure gauge.
  3. Increase engine speed to 2000 rpm.
  4. Normal pressure should be below 1.25 psi. Any reading above this would indicate a restricted catalytic converter or exhaust.
Windings like in this ignition coil can develop electrical opens that cause stalling when warmed.

Windings like in this ignition coil can develop electrical opens that cause stalling when warmed.

4. Windings and Coils

There are a number of components that integrate a winding or coil. Coils can also fail after exposure to high temperatures for a long period of time. A winding can brake and create an electrical open that may not manifest itself until high temperatures return.

Fuel Pump:

Internal problems in the motor assembly of a fuel pump can also lead to a stall-while-driving condition. A common problem is a broken or electrically open windings or coils.

As the fuel pump runs, it warms up. Eventually, heat will move the broken wire away from the coil and cut the flow of electricity, causing the fuel pump to shut down. The vehicle will start again once the pump cools and the opening in the winding or coil closes again.

A worn out pump may behave in a similar manner, stalling the engine intermittently. However, the engine may start up again soon after it stalls, or not start again, depending on the particular problem. Watch the following video for an example of this type of fuel pump problems.

Ignition coils and modules:

A similar problem will appear on vehicles with a single ignition coil that have an electrical open in a winding or coil, or a faulty electrical connection inside an ignition module.

When engine heat rises, the faulty coil or small electrical connections in the module will expand, cutting out current flow and shutting down the engine.

Consult your vehicle repair manual, if necessary, before replacing any components.

Crankshaft position sensor (CKP):

A similar intermittent problem may be caused by an open winding in a CKP. The vehicle will run without issues until temperature rises, the coil inside the sensor opens, and the engine stalls. The engine will start and run again when it cools until temperature goes up again.

A faulty CKP sensor may also cause an intermittent stall condition after a few minutes of engine operation. In some cases, a faulty CKP sensor won't even cause the check engine light to illuminate. If necessary, consult your vehicle repair manual.

You may check the crankshaft position sensor when cold and after engine stalls using an ohmmeter.

Passages in the IAC valve, next to the throttle body, may clog with fuel varnish.

Passages in the IAC valve, next to the throttle body, may clog with fuel varnish.

5. Idle Air Control (IAC) Valve

This is another common fault that may cause the engine to stall while driving. This usually happens when coming to a stop.

The car's computer uses the IAC valve to control idle speed. As commanded by the computer, the valve bypasses the throttle plate and injects more air into the engine when the throttle plate closes.

It's not uncommon for dirt and fuel varnish to restrict valve passages. If not enough air can pass through the valve when the engine requires, the engine may stall when you come to a stop.

Often, car owner's can check themselves the condition of IAC valve passages by removing the valve. This is attached to the throttle body by, usually, two mounting bolts. The valve is usually accessible. Once removed, you can check and clean valve and throttle passages using throttle cleaner. Follow the instructions that come with the product.

Also, it may be necessary to test IAC valve operation and circuit. If necessary, consult your vehicle repair manual.

Dirt may interfere with MAF sensor wires.

Dirt may interfere with MAF sensor wires.

6. Mass Airflow (MAF) Sensor

Basically, the MAF sensor measures air density as it flows into the intake manifold. The car's computer uses this measurement to calculate throttle opening and air volume. This engine load input helps the computer control fuel injection and ignition.

A common problem with MAF sensors is debris and dirt that accumulates around the wire sensor, causing a faulty signal to be sent to the computer. You may notice the car sputtering and possibly stalling when stopped.

You can buy MAF sensor cleaner at most auto parts stores and clean the sensor yourself. Follow the instructions that come with your product.

Carbon buildup will interfere with EGR valve operation.

Carbon buildup will interfere with EGR valve operation.

7. Exhaust Gas Recirculation (EGR) Valve

A similar problem as that of a restricted IAC valve can happen with an EGR valve. The valve allows measured amounts of exhaust gases back into the cylinders to control temperature and harmful emissions (Nitrogen Oxides NOx).

Over time, valve passages clog with carbon buildup and can prevent the valve from closing properly, which may cause the engine to stall.

In many vehicle models, removing, inspecting and cleaning the EGR valve is not difficult. Depending on your particular model, you need to remove two or more mounting screws and, possibly, disconnect an exhaust pipe.

If necessary, consult your vehicle repair manual.

Check the air filter housing and hose between the MAF sensor and throttle body when searching for vacuum leaks.

Check the air filter housing and hose between the MAF sensor and throttle body when searching for vacuum leaks.

8. Vacuum Leaks

Another problem is vacuum leaks. Just like a faulty MAF sensor that can't report to the computer the actual air density entering the engine, a vacuum leak through a vacuum hose, throttle gasket or intake manifold, introduces unmetered air, upsetting the best air-fuel ratio the computer has calculated from the information it has.

This problem may be more evident at idle. Your car may stall during cold idle or even when stopping.

Checking for vacuum leaks can be tricky. Inspect the hose connecting the air cleaner assembly or MAF sensor to the throttle body. Also, take a close look at vacuum hoses. Spraying carburetor cleaner around the gasket areas of the throttle body and intake manifold may help locate vacuum leaks. If you notice a change in idle speed when spraying around a gasket area, you've found the problem.

Locate and test the MAP sensor.

Locate and test the MAP sensor.

9. Manifold Absolute Pressure (MAP) Sensor

The MAP sensor measures vacuum or pressure in the intake manifold. A MAP sensor can also fail and send incorrect data to the computer.

Check the sensor's vacuum hose, and, if necessary, test the MAP sensor.

The TPS attaches to the throttle body.

The TPS attaches to the throttle body.

10. Throttle Position Sensor (TPS)

The TPS reports to the car's computer the rate of throttle opening and relative throttle position. The sensor has an internal resistance that changes the voltage signal sent to the computer with changes in throttle opening or position.

The device's internal resistance may develop dead spots that can interrupt the voltage signal intermittently, causing the computer to adjust the air fuel ratio incorrectly. The car may stumble, stall intermittently, or even prevent the engine from starting, depending on the fault and vehicle model.

You can test the TPS using an ohmmeter at home.

11. Engine Coolant Temperature (ECT) Sensor

The ECT tells the car's computer when the engine is cold or overheating. The computer uses this information to adjust the air-fuel ratio.

During a cold start, the computer adds fuel to the mixture to prevent the engine from stalling. Also, if the sensor reports to the computer that the engine is overheating, extra fuel is added to the mixture to lower the mixture's temperature.

If the sensor becomes faulty, it can trick the computer into adding fuel to the mixture unnecessarily, which may cause the engine to stall. You can also test the ECT sensor at home following a simple procedure.

Locate the data link connector on your vehicle and download trouble codes.

Locate the data link connector on your vehicle and download trouble codes.

12. Making the Most of Your Diagnostic and Repair Time

There are a number of sensors or systems that can cause your car to stall while driving.

Often, you won't have the help of a diagnostic trouble code to help you. But this guide can help you start hunting for the culprit behind the fault to get your car back on the road sooner.

However, even if your check engine light comes on, always troubleshoot any component you intent to replace when possible. Car computers don't always point to the source of the problem but the component or system which parameters where out of bounds. This will shorten your diagnostic and repair time.

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.

Questions & Answers

Question: What causes a 2003 Mazda Tribute to stall slightly going up inclines and the instrument panel bottoms out and then when I'm over the incline they readjust to normal?

Answer: It seems like a bad electrical connection. If both the engine seems to lose power and the instrument panel dims or goes out, check the battery connections. A loose, corroded or damaged wire may cause this problem. Idle the engine and wiggle the cables and see what happens. Hope this helps. You may try checking for voltage drop. You may find engine grounds with too much resistance. This other post may help:

https://axleaddict.com/auto-repair/Automotive-Volt...

© 2019 Dan Ferrell

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