Car won’t start, shows key not detected?

2018 FORD FOCUS
140,000 MILES • 2.0L • AUTOMATIC
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NAIYASPAPAYAS
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When I crank the engine, Key Not Detected comes up on the dash and there’s no clicking or clanking. Battery was reading 8.9v, after a battery swap and a 50amp midi fuse swap there’s still no change other than a soft thumping in the engine bay when attempting to start the car. Battery is now reading 11.8v steady. Codes on dash when in TEST mode read C101_00, C121_00, C140_00, C151_00, 1607_87, 1607_82. Any ideas what could be causing the power failure?
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Jul 12, 2026 at 11:38 PM
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STRAILER
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So, you say battery swap, is it a new battery? I would use a voltmeter to confirm the battery voltage first. Here is a guide to help you.

https://www.2carpros.com/articles/how-to-use-a-voltmeter/

Please go over this guide and get back to me.


Jul 13, 2026 at 2:58 PM
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STRAILER
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You will get all of the codes you see if the battery is low.
Jul 13, 2026 at 5:07 PM
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NAIYASPAPAYAS
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I just ordered the voltmeter, should arrive tomorrow. I’m the meantime, the battery I swapped it with is brand new if that provides any more information
Jul 13, 2026 at 5:17 PM
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STRAILER
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Okay, then the battery should be good but if we know the voltage it will help us not get lost in the diagnosis. Let me know.
Jul 14, 2026 at 12:43 AM
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NAIYASPAPAYAS
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Checked the cars TEST mode voltage a few times throughout the day and reads 11.8v every time but will update with voltmeter voltage also. My guess is I swapped the wrong 50 amp midi fuse as I didn’t check them prior, just followed a tutorial and swapped the same one that was swapped in the video. Ordered a couple of those as well to switch out the rest
Jul 14, 2026 at 1:13 AM
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STRAILER
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Yep, good call, also how dot he battery cable end look, are they corroded away?
Jul 14, 2026 at 1:30 PM
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NAIYASPAPAYAS
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The negative side of the battery connections were corroded but I scrubbed them clean with a wire bristle brush and they look good as new. Hoping the fuse swap does the trick, stumped after that.
Jul 14, 2026 at 4:37 PM
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STRAILER
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Yep, sounds good, let me know and I can help if it doesn't.
Jul 15, 2026 at 4:30 PM
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NAIYASPAPAYAS
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No change after swapping all the fuses.
Jul 15, 2026 at 5:19 PM
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STRAILER
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Okay, what is the voltage of the battery? also are all the battery cable leads connected?
Jul 15, 2026 at 6:29 PM
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NAIYASPAPAYAS
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All cable leads are connected and I cleaned up some light corrosion on the negative side. Voltage from the car is reading 11.8 and doesn’t change when turning key
Jul 15, 2026 at 6:32 PM
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STRAILER
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Yes, we are to check it will a volta meter so we know if the problem is the battery or the car.
Jul 15, 2026 at 6:45 PM
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NAIYASPAPAYAS
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Still waiting on that voltmeter, sorry for the lag. I just checked it and battery is sitting at 11.6 now and jumps to 11.7 when turning the key. Voltmeter should be delivered by the end of the day
Jul 15, 2026 at 7:19 PM
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STRAILER
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Okay, sounds good.
Jul 15, 2026 at 11:07 PM
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