The most common reason for a car stalling with a check engine light on, is a problem with the fuel or air supply to the engine. A rich or lean fuel mixture will trigger an error with the car’s ECU and this will turn on the check engine light on the dashboard.
A problem with the supply of fuel or air can be caused by bad or dirty spark plugs, a faulty ignition coil, a bad fuel injector, a faulty mass airflow sensor, a sticky idle air control valve, or a problem with the engine timing.
What causes a check engine light and a car to stall? (6 Common Reasons)
Common causes of stalling with the check engine light on include a faulty oxygen sensor, a clogged fuel filter, a malfunctioning ignition coil, or a problem with the mass airflow sensor.
There could also be a problem with the air/fuel mixture being fed into your engine. One common cause of this issue is a faulty mass airflow sensor, which can cause the engine to receive incorrect information about the amount of air entering the engine.
The ECU monitors the running of the engine in real-time by using data received from the numerous sensors located around the engine. If it detects a problem, then it will turn on the check engine light.
When trying to diagnose the problem it’s best to start by looking at any error codes that are stored in the ECU memory.
Engine error codes will give an indication as to whether the problem is caused by a lack of fuel, air, a well-timed ignition source or a faulty sensor. Sometimes a check engine light can even be caused by a weak or bad battery.
Cause 1: A blocked fuel filter
A common cause of car stalling and a check engine light is a blocked, or partially blocked fuel filter. Fuel filters are often serviceable items and should be changed at regular intervals.
If a fuel filter is blocking the passage of fuel to the fuel injectors then this can cause a car to stall, especially if the car is accelerating and needs extra fuel. A lack of adequate fuel when expected may cause a misfire in the affected cylinder and this can trigger a check engine light.
A partially blocked fuel filter may adversely affect the fuel pressure within the fuel lines and this can also cause a check engine light. A lack of fuel in the engine cylinders will leave an engine running lean and this can be picked up by the oxygen sensors if too much oxygen is in the exhaust fumes.
Cause 2: A Bad fuel injector
Bad fuel injectors are another very common reason why a car may stall with a check engine light.
Fuel injectors are responsible for getting the fuel into the engine cylinders through a technique known as direct fuel injection. It’s a very precise process that is controlled by the ECU and is dependent on adequate fuel being available in the fuel lines when the engine is running.
Fuel injectors can fail are if they become blocked or if they start to leak. This can affect the injector’s ability to create a precise fuel spray in a cylinder when called needed.
If a cylinder doesn’t receive the expected amount of fuel at the right time then this may cause a misfire that can cause a car to stall. The check engine light will usually come on indicating a range of problems such as a faulty fuel injector, lack of fuel pressure, or out-of-range oxygen sensor readings.
Cause 3: A Failing Fuel Pump
A bad fuel pump is another potential cause of problems with the fuel pressure and fuel delivery in a car. This is another common reason for a car to stall and can definitely trigger a check engine light.
The job of the fuel pump is to maintain fuel pressure in the fuel lines and to pump fuel to the fuel injectors via the high-pressure fuel rail. A failing fuel pump may operate erratically and this can lead to a shortage of fuel in the engine cylinders when it is needed.
Just like with a blocked fuel filter or bad fuel injectors, a bad fuel pump will trigger the check engine light if it causes a drop in fuel pressure that leads to engine misfires or the car stalling.
Cause 4: Bad Spark Plugs
One or more bad spark plugs can also cause an engine to run rough, and this can cause your car to stall and usually, the check engine light will come on too.
Bad spark plugs can happen for a number of reasons. Spark plugs have a limited life span and should be changed at regular intervals when the car is being serviced.
Old spark plugs can create problems with the proper combustion of fuel and this can lead to engine stalling, bad fuel economy, engine misfires, and possible damage to the catalytic converter.
A spark plug can prematurely fail if there is a problem with the engine running rich over a long period of time. Carbon build-up within the engine cylinder can damage the electrode tip, resulting in a plug that can no longer spark properly.
Spark plugs can also fail if there is a more serious problem like oil or coolant getting into the engine cylinders. This can also cause a car to stall and a check engine light to come on.
Cause 5: A faulty engine sensor
Faulty engine sensors can also cause a car engine to misbehave and stall along with causing a check engine light.
Modern engines have dozens of sensors fitted that are essential for keeping them running efficiently. Sensors usually report vital engine statistics in real time to the ECU.
They are used to keep track of all sorts of different engine functionality and engine conditions such as the volume and pressure of air in the intake manifold, the engine oil temperature and pressure, fuel pressure, engine timing, and exhaust gas composition.
Cause 6: A Bad Idle Air Control Valve
A bad or sticky idle air control valve can cause a car to stall when idling if it is not allowing enough air to get into the engine when the throttle valve is closed.
The idle air control valve keeps the engine running when the vehicle is stopped. It does this by controlling the idle speed of the engine by facilitating a flow of air that bypasses the throttle valve when it is closed.
The amount of air needed to keep the engine running is a lot less than when the vehicle is moving and this air flow is electro-mechanically controlled by the ECU by opening and closing the idle air control valve.
An idle air control valve can fail in a number of ways. The valve flap can become stuck open or partially open, affecting the idle speed of the engine. If there isn’t enough air getting into the engine then this can cause it to misfire, shake or stall completely.
A faulty idle air control valve will cause a check engine light and error code P0505 will usually be stored in the ECU memory.
What Next – How To Diagnose And Fix A Check Engine Light When The Car Is Stalling?
It’s a good idea to start with a diagnostic readout of the ECU to see what error codes have been recorded. If you are lucky, then there will only be one or two error codes that point to a specific engine component that you can then test.
1. Start with a readout of the ECU. Check to see what error codes are present in the ECU memory. If the car can still be started then clear the error codes from memory and take it for a short drive to see if you can replicate the problem. If the car stalls again then check the ECU again for new error codes.
2. Check the Spark plugs and filters. If there are no OBD codes pointing to a specific problem then the next step is to check the serviceable items in the engine for their condition. Remove each spark plug and check their condition and ensure they are dry and have no signs of contamination. Check the air filter and replace it if it looks clogged or black. If there is a removable fuel filter check this too and replace if necessary.
3. Check the idle air control valve and throttle body. A stuck idle air control valve will cause a car to stall when idling. If there is a problem with the electronic circuitry within the valve then this will create an engine error code P0505. Otherwise, it’s possible for the IAC to become clogged or carbonated so removing it and the throttle body for cleaning may help.
4. Decipher engine error codes. If there are codes present then these might point to a problem with the fuel pump, ignition coils, injectors or sensors such as the mass airflow sensor. Investigate each of these codes further to help diagnose the problem. Below is a list of common error codes and their meaning:
| OBD Error Code | Error Code Meaning |
| P0301 – P0306 | Cylinder misfire. Check spark plugs, igniton coil, fuel injector |
| P0087 | Bad fuel pump, fuel pressure sensor |
| P0101 | Bad mass airflow sensor. Check for dirt and test for problems |
| P0505 | Idle Control System Malfunction. Test idle air control valve |
| P0524 | Engine oil pressure too low. Check oil level, oil pressure sensor |
| P050B | Ignition timing fault. Check spark plugs, crankshaft position sensor, camshaft position sensor, throttle position sensor |
My car has been stalling and the check engine light is on. Could it be an issue with my fuel pump, and how can I confirm that?
My car stalls and the check engine light comes on frequently. Could it be a simple issue I can diagnose myself, or should I take it directly to a mechanic?