An engine that keeps running after the key is removed (or the push-button is pressed off) has a stuck ignition switch, a welded starter relay, dieseling (run-on), or a wiring fault that keeps power to the fuel pump and ignition. This is unusual but specific - and serious, because you cannot shut the engine off normally. Fixes are usually electrical, not mechanical.
Until this is fixed, you can shut the car off by stalling it: put it in gear with the brake firmly held, then release the clutch (manual) or shift into low gear at idle (automatic). Or unplug the fuel pump relay. Get this fixed before driving again.
Each cause is rated by likelihood, repair cost range, DIY difficulty, and severity. Start with the highest-probability cause and work down.
The RUN-position contacts inside the ignition switch are welded or stuck. Even with the key out, those contacts are still passing power. Replace the ignition switch electrical part (not the lock cylinder).
On older carbureted or early fuel-injected engines, hot carbon deposits can ignite fuel without spark - engine 'diesels' for several seconds after key-off. Caused by hot spots and high idle. Fix: tune-up, top engine cleaner, lower idle.
A relay's contacts can weld closed after years of use, keeping power to the fuel pump or ignition coils even with the key off. Pop the under-hood fuse box, find and pull the suspect relay - if engine dies, the relay is your answer.
Improperly installed remote-start systems can hold the ignition circuit live after key-off. Disconnect the aftermarket unit as a test.
On modern push-button-start cars, the PCM or BCM controls when to cut fuel and spark. A module software glitch or reflash issue can prevent shutdown. Dealer scan tool diagnoses.
A rubbed or pinched wire shorting power directly to the ignition or fuel pump circuit will keep things running with the key off. Often after recent electrical work or accessory install.
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If your scan tool is showing one of these codes alongside this symptom, that is your starting point. Click any code for the full diagnosis.
🔬 Get my $5.99 AI repair report →Power is still reaching the fuel pump and ignition coils even though the key is out. Top causes are a stuck ignition switch (welded contacts), engine dieseling on older cars, a welded fuel pump or ignition relay, or aftermarket alarm/remote-start wiring.
Three options. 1) Put it in gear with the brake on and stall it (manual) or shift into Drive at idle with brake firmly applied (automatic). 2) Open the under-hood fuse box and pull the fuel pump relay. 3) Pinch the fuel line if accessible. Then get the car flatbed-towed to a shop.
Yes. You cannot reliably shut the engine off, which is a serious safety issue. The car could start moving in a parking lot, overheat overnight in your garage, or refuse to be parked. Tow it - do not drive it.
On older engines, hot carbon deposits inside the cylinder can ignite fuel even without spark - so the engine 'diesels' for a few seconds after key-off. Fix with top-engine cleaner, carbon cleanup, and lower idle setting. Modern fuel-injected engines rarely diesel because fuel cuts off at key-off.
Yes. An improperly wired aftermarket system can latch the ignition circuit on. Disconnect the aftermarket unit's connection at the ignition harness as a test. If the car shuts off normally, the aftermarket is the cause.
Ignition switch electrical: $80-300. Relay: $10-40. Fuel pump relay: $20-80. Aftermarket diagnosis/removal: $50-300. PCM reprogram: $100-300. Carbon cleanup for dieseling: $100-300.