Hood open warning when hood not open

RK1975 · May 28, 2022

My Lexus Ct200h (2013 model) has suddenly decided that my hood is open when it is evidently not. This coincided with a warning that my key fob Battery is low and the car alarm deciding to give a couple of renditions of its own. I've replaced the Battery and no alarms since but I'm still getting the hood open warning.

I've opened the hood (which was firmly closed prior) and seen that the mechanism is rather rusty (on the hood bit and on the frame), so I'm guessing that this may be the cause of the warning. Does that sound plausible or could something else be going on? If it is rust, would cleaning it up sort this problem (if so, what's the best way?) or am I in for a costly repair? Tbh, I'd be happy with the sensor disconnected if I knew how!

Any advice appreciated.

Herbie · May 28, 2022

Never had a CT so I don't know for sure but, most cars usually have a 'plunger' type of switch mounted facing upwards, somewhere around the radiator or the bonnet catch, so that when the bonnet is closed it presses the plunger down.

It probably has two wires to it so either just pull them off the switch and connect them together, or replace the switch.

Las Palmas · May 28, 2022

Do not know where the switch telling the can-bus that the bonnet is open is, but as UK is a country with rather a lot of water coming down from above, it could be the same problem as Citröen, Peugeot and probably other brands have had in northern countries. Ground (negative connection to car body) was placed in front of the car where water is splashing from driving on wet roads (and in winter also salty water) causing corrosion and thus lacking contact to body of car. Had a Peugeot Rally where whole instrument cluster was blinking and telling that something was wrong.

ColinBarber · May 28, 2022

5 hours ago, Las Palmas said:

Do not know where the switch telling the can-bus that the bonnet is open is, but as UK is a country with rather a lot of water coming down from above, it could be the same problem as Citröen, Peugeot and probably other brands have had in northern countries.

If the French brands put all individual sensors on the can-bus then that might start to explain why they are so unreliable. Toyota individually wire sensors back to the ECUs - certainly on the CT.

7 hours ago, RK1975 said:

Tbh, I'd be happy with the sensor disconnected if I knew how!

If you just disconnect the sensor then you are unlikely to be able to set the alarm.

The sensor is built into the latch assembly. You should check the wiring that comes from it is undamaged and is correctly pushed into the wiring connector located a short distance below the latch.

You could try cleaning it all up (you may have to unbolt it from the vehicle) and possibly the microswitch can be individually replaced, but the only the whole assembly is available from Lexus:

https://lexuspartsdirect.co.uk/product/lexus-ct-phase-1-bonnet-latch/

You probably could adapt the wiring to fool the system into thinking the bonnet is correctly closed but you would lose some security protection if you did - and you have to take into account the loop through circuit that goes in parallel with the switch wiring which protects the vehicle in case some just tried to disconnect the electric connector in an attempt to defeat the alarm.