Why Can't My Proton Saga BLM Start?

You own a Proton Saga BLM and one day when you turn the ignition key, the car doesn't start as usual. Instead, the engine coughs and the battery and alternator light comes on. But you've only recently changed the car battery. What could possibly be stopping your car from coming to life?

There may be many reasons why your Proton Saga BLM doesn't start when you turn the ignition key, but here is one solution which worked for me.

Disclaimer: My Proton Saga BLM is an automatic transmission, 1.3 liter model and registered in 2010.

The key unit of the Proton Saga BLM is made of plastic housing, and it houses many important electrical components inside. Many years of constant use (i.e. gripping the plastic housing and turning the key to start the engine) result in the plastic housing cracking and giving way. One of the effects of wear and tear is a hole forming in the plastic housing, near the metal part of the key.

Everything looks normal from the top

On closer inspection, the plastic housing has a huge crack, exposing the insides

Next to this hole lies a sensor which is crucial to starting the car. The sensor is rectangular and measures approximately 1cm by 0.5cm. Through wear and tear, if the hole becomes big enough, or if the plastic housing becomes wobbly or nonfitting, chances are the sensor may fall out of the plastic housing. This results in the car being unable to start even if you insert the ignition key and turn it to start the engine.

Plastic housing opened, showing position of sensor within it

Plastic housing opened, with sensor removed

Conclusion.
If you observe your key's plastic housing has become loose or cracked, chances are the sensor has fallen out. Open the plastic casing to confirm that the sensor has fallen out. Try to recall where you last applied pressure to the plastic housing. Usually it would be the last time you started or stopped the car... in which case, check your driver-side car mat. Replace the sensor, and tape the plastic housing nicely together.