Your car is designed to run like a well-oiled machine, but sometimes that machine struggles in unexpected places. There’s not always a warning light to alert you of this, but sometimes your car will be driving fine at road speed, only to die when you slow down and stop. If your engine shuts off at low speed, contact a mechanic immediately for a thorough inspection.
Common reasons for this to happen:
Malfunctioning transmission: In a car with an automatic transmission, the torque converter takes the place of the manual clutch and is responsible for transmitting power. If the torque converter is broken, or if there is a low fluid level in the transmission, the converter will not do its job, and the car will be unable to maintain power at low speeds, which causes the engine to shut off. A defective TCS or torque converter solenoid can also cause this issue.
Low fuel pressure, dirty or defective fuel injectors, or broken fuel pump: The fuel pump is responsible for transferring fuel from the tank to the engine. A malfunctioning fuel pump can result in low fuel pressure, which means that there is an inconsistent stream of fuel to the engine. At high speeds this doesn’t matter as much, but at low speeds a temporary pause in the fuel stream is enough to kill the engine. The fuel injectors are responsible for spraying a measured amount of fuel that is ignited by the spark plugs at the proper time. Injectors can become clogged or dirty over time resulting in erratic spray or no spray at all.
Bad oxygen sensor or mass flow sensor: The oxygen sensors and mass flow sensor determine how much oxygen is entering the fuel stream, and helps the vehicle adjust the air-to-fuel ratio. If there is too much or too little oxygen, your vehicle will not have optimal power. Just like with low fuel pressure, the car will continue to operate at driving speeds, but this suboptimal power won’t be able to fuel the vehicle as it slows down.
Loose or corroded wires in wiring harness: An inconsistently firing ignition will result in an easily stalled engine. If the wires don’t have consistent, constant, and reliable connection with the ignition circuit, the vehicle can lose voltage quickly, and it won’t have the power it needs to keep running as you slow down.
Faulty idle air control actuator: The idle air control actuator controls the engines RPMs when it is idling. This actuator receives information from the electronic control unit (ECU) so it knows at what RPM to keep the engine for a smooth and safe idle. When the actuator malfunctions, the engine gets no signal for idling speed and stops working.
Clogged or restricted EGR Valve: If your EGR valve is clogged, dirty, or defective it can cause your car to stall, idle erratically, or sputter, depending on whether it is stuck open or closed.
What to expect:
A top-rated mobile mechanic will come to your home or office to determine the source and cause of the stalling condition, and will then provide a detailed inspection report that includes the scope and cost of the necessary repairs.
How it's done:
The mechanic will likely need to test drive your vehicle to see if the problem can be replicated and will listen to the engine at idle to identify any misses, backfires, or other unusual noises. Next, the mechanic will use a scan tool to access the engine control unit or transmission control computer to find any information on stored codes.
Based on the engine performance, test drive and the diagnostic information, the mechanic will pinpoint where the issue is coming from, and let you know what parts need to be replaced or cleaned. Please be aware that this make take some time as oftentimes multiple items have the ability to cause this issue and the mechanic will often have to disassemble and inspect several parts before he or she can make a proper diagnosis.
How important is this service?
If you notice your vehicle stalling when you slow down and stop, park the car in a safe place and book a mechanic to perform an inspection as soon as possible. It is unsafe to continue driving under this condition and could result in further damage to your vehicle.