Shuts off the truck and when I let off the brake it won’t start?

RYAN SWENSON

MEMBER
2017 FORD F-150
3.5L
V6
TURBO
4WD
AUTOMATIC
68,000 MILES

My truck listed above Limited won’t always start. When the truck is cold it always starts, but when I’ve been driving it sometimes it won’t start again. I could be driving and come to a stop at a stop light and the start stop kicks in and shuts off the truck and when I let off the brake it won’t start. Other times I’ll park after driving, go into a store and it won’t start when I get back in. I’ve put a new battery in it and checked fuses and made sure relays are seated, but can’t figure this one out. Love the truck but getting frustrated. Thanks for any help!

1 Reply

JACOBANDNICKOLAS

MECHANIC
109,740 POSTS

Hi,

What you described sounds like a faulty crankshaft position sensor. Oftentimes, when they start to fail, heat adversely affects them causing a no start or stalling. Then, when they cool off, they work again.

Do me a favor and look through this link and let me know if it seems to mirror what you experience.

https://www.2carpros.com/articles/symptoms-of-a-bad-crankshaft-sensor

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We have two things you can try. Since the sensor may or may not turn on the check engine light, we need to see if spark is lost to the plugs or if the RPM signal is lost.

If you have a live data scan tool, plug it in when it won't start and crank the engine. Check for an RPM signal. If there is none, there is a good chance it's the sensor.

Or, you can check for spark to the plugs. Here is a link that explains how to check:

https://www.2carpros.com/articles/how-to-test-an-ignition-system

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If you determine the sensor is bad, here is a link that shows in general how one is replaced. You can use it as a guide to help.

https://www.2carpros.com/articles/crankshaft-angle-sensor-replacement

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The pics below show the directions and pics specific to your vehicle for removal and replacement.

Let me know if this helps.

Take care,

Joe

See pics below.

Images (Click to make bigger)