If your car stalls and the check engine light comes on, it may be simple to fix the problem or it could be a sign of a bigger issue that is only going to get worse if left unresolved. So what could be causing your car to stall and how do you go about diagnosing and fixing it?
A check engine light and a car that is stalling can have a number of different causes. The most common causes include a problem with the supply of fuel, 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.
The severity of the problem can sometimes be judged quickly, depending on whether or not the car restarts after stalling. Bad engine sensors or problems with the fuel supply may cause a car to stall intermittently with a check engine light that clears after a restart.
However, if the car stalls and won’t restart then this suggests a more serious problem such as a faulty fuel pump or a problem with the engine timing.
What causes a check engine light and a car to stall? (6 Common Reasons)
When a car stalls and the check engine light comes on, this usually points to a problem with the supply and management of fuel or air to the engine or a problem with the combustion process.
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.
There are lots of different reasons why the check engine light can come on and there are also lots of reasons why a car can stall. 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 by a faulty sensor.
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.
Some fuel filters are located in the fuel tank or they may be located along the fuel line. They can become blocked or damaged by contaminants or water vapor in the fuel tank.
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.
A fuel injector can become blocked if the tip or nozzle becomes dirty, and partially blocked. Hard hydrocarbon deposits inside the tip of the injector can build up over time and block the injector.
Leaky injectors can also occur with the failure of the O-ring where the injector seals with the engine. These rubber O-rings can become hard and brittle over time from constant heating and cooling of the engine.
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 as 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.
A fuel pump that is failing can sometimes be noisy, and along with stalling the car can also make your car difficult to start and create a rough driving experience with an overall lack of engine power output.
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
A car that has stalled when driving or idling usually does so because of a lack of sufficient air, fuel or ignition source to keep the engine going. It’s useful when trying to diagnose the problem to look at each of these areas separately to try and pinpoint the problem.
If the car has stalled with a check engine light present, it can often make it easier to find the source of the problem. This is because a check engine light usually means that an engine error code has been stored in the ECU.
So for this reason 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 |
FAQ – Car stalling and check engine light
1. Why is my car stalling out when I stop?
Your car may be stalling when idle for many reasons. The most common reasons include a faulty idle air control valve, a sticky throttle body or faulty throttle position sensor and a bad mass airflow sensor or dirty air filter.
There may also be a problem with the fuel pressure or blockages in the fuel lines. If there is a vacuum leak due to a leak around the intake manifold or a split turbo hose if the car has a turbo fitted this can also cause a car to stall.
2. Can low oil cause a check engine light?
Yes, low oil levels in the engine can cause the check engine light to come on if the oil pressure sensor detects that the oil pressure has dropped below a safe threshold.
Low oil can be caused by not checking the oil and topping it up regularly if necessary. It can also be caused by oil leaking from a bad head gasket or internally worn piston rings and valve seals can lead to oil being burnt off during combustion.
3. Can low coolant cause a car to stall?
Yes, low coolant levels can cause a car to stall if the engine overheats or if the engine ECU shuts down the engine to prevent damage if the temperature cannot be controlled.
Low coolant levels will cause an engine to overheat and this can cause damage to the cylinder head and engine block over time causing cracks an further leakage of oil and coolant.
Leakage of these liquids into the engine cylinders can cause misfires and damage to the pistons, valves, spark plugs and catalytic converter causing the car to stall when driving.