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Hi,
We own a 2014 Manual titanium Ecosport for the last 3 years and we love it, it’s a wee car with great fuel economy and it didn’t give us any problems... until now. It is nothing big but rather annoying and needs to be fixed.
It started a couple of weeks ago, I noticed the reverse light wasn’t working anymore and the car’s reverse sensors won’t work neither.
The car does reverse but no sensors on and no light.
So today I took the light bulb off and drove to the shop. Leaving the house I reversed and noticed that the sensors were working again ! I just presumed by then that the bulb was the issue.
I installed the new light bulb and I got back to where I started: no reversing light, no sensor. It’s like the ÉCU doesn’t know I’m reversing.
I also put a new fuse at the «*reverse lamp*» in the Passenger’s fuse box but it didn’t fix the issue.
Not sure where to look at right now... wiring issue ?
HELP
 

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Hi and welcome to the forum :D

The way the circuit works is that when you select reverse, the reverse switch operates and puts on the reversing light, and the same 12V supply also energises the reversing sensors.

What I think the culprit is, is an earth fault in the circuit, and when the bulb element is in, it is tracking down to earth and not giving you the correct 12V voltage for the bulb or reversing circuit.

Earth fault...
I would say you have a bad earth fault from the bulb down to chassis earth. You can get this on older cars. The current flows through the bulb resistance and added to the fault resistance, reduces the voltage to the sensors. In diagram below you see normal circuit with 12V available at bulb and sensors, but with a resistance at the earth boss (ie, a bad earth) you may get say only 4V for the sensors, and the other 8V across bulb resistance and fault resistance. So nothing works.

With bulb out you will then get 12V for the sensors.

You have to trace the negative side of the bulb holder wire back to the threaded earth boss that's welded on the chassis, it will be in the boot area. Undo the bolt, and remove the earth wire or earth wires, and clean the threaded earth boss with an emery cloth to remove rust , grime, and dirt, to get a good earth, and reconnect. That should sort it.

If you have an electrical meter you can check if you are getting a good earth or not, by the meter set on ohms, you should get a direct short circuit, from negative side of bulb holder down to earth, but if there is an earth fault, ie a bad earth boss, it will read some impedance.

Easy method...
An easier method, which I have used in the past with earth faults, is just run a new earth wire from the earth side of the bulb holder to an new earth point on the chassis. (a bolted item on the chassis is good, just remove bolt and fix the new earth wire to it).

These earth faults at the earth bosses of the chassis is usually an older car fault where earth bosses have to be cleaned with emery paper. The most common earth fault is rear lights dimming, or more than one lighting circuit lighting operating on dimmed power, as the bulb elements act as bridges to other circuits, if earths are not working correctly.

 
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