Causes and Solutions for Occasional Engine Warning Light (Mazda Demio DBA-DE3FS)

We received a third-generation Demio with an occasionally illuminating engine warning light.

From the Familia to the current Mazda2, Mazda’s lightweight vehicles have always featured remarkably mild and straightforward rear-end behavior. I always find it interesting to see how this consistent tuning is inherited within the manufacturer whenever I drive a Mazda lightweight vehicle.

Perhaps Mazda’s engineers hope people will enjoy their lightweight vehicles, as they still offer manual transmission options in the current Mazda2 while other manufacturers have been gradually phasing them out.

2010 model DBA-DE3FS ZJ 4AT Mileage 87,000km

Now, the basic scanner diagnostic showed high input voltage from the knock sensor.

Based on the over 200 parts in inventory and numerous repair cases online, I determined that the knock sensor itself was definitely faulty.

The knock sensor is located on the side of the engine cylinder block.

It works to maximize fuel efficiency and power output by monitoring engine knock and advancing the ignition timing as much as possible.

When knock impact (sound) occurs, a weight inside the sensor receives it, and a piezoelectric element adjacent to the weight generates electricity.

The engine ECU detects this electrical signal and appropriately retards the ignition timing.
The knock sensor on the Demio’s ZJ engine was located under the intake manifold, not in an easily accessible location.

When beginning disassembly, the various connection points were relatively easy to separate. The only challenging part was the large nut on the somewhat stuck EGR pipe.

For a Japanese car just over 10 years old with less than 100,000 km, I occasionally encountered connectors in a shape prone to deterioration and damage, causing momentary tension. However, upon touching them, I found they still retained flexibility, allowing me to proceed with the work confidently.

Behind the removed intake manifold appeared the hexagonal knock sensor.

For removing and installing sensors with attached wiring, a crow foot wrench like this is convenient and makes torque management easy. Since generic tools for 24mm hexagons are often large and long, particular attention should be paid to tightening torque when dealing with sensors like the knock sensor that are secured with thinner screws.