Without a properly working electrical system, our freshly installed K-Series engine won't do much besides looking good in our engine bay.

But what's actually required to install, replace, and rewire to get a K20 motor firing up in a 01-05 Honda Civic?

Step 1) C101 Connector

This is the main connection between the K-Series engine harness and the chassis harness of the car. It establishes proper communication between the engine's sensors, the engine control module (ECM), and other subsystems in your car.

Here, we have to relocate a bunch of wires since the pinout of the K-Series engine harness' C101 connector differs from the stock D-Series connector.

Step 2) Oxygen/AFR Sensors

The oxygen or air-fuel ratio sensors are part of the exhaust system and measures the amount of oxygen in the exhaust gases. Most models have two sensors, the HX model has three. They're mounted in front and behind the catalytic converter.

The sensors behind the converter are used to determine the efficiency of the converter itself - converting the toxic exhaust gases of the engine into less-toxic carbon dioxide.

In our K-Swapped EM2, ES1, or ES2, we can simply connect it to the original chassis harness connector to get it working.

Things become more tricky with the sensor in front of the converter.

The sensor helps the engine control module to calculate the right amount of fuel that gets sprayed into the cylinders.

Unfortunately, this sensor wasn't part of the chassis harness of our Honda Civic as is the case with most cars that came with a K-Series engine from factory. Since there is no connector we can hook the sensor up to anymore, we need to run the wires separately to the ECM.

In addition, we need to replace the old sensor with an air-fuel ratio sensor that can be found in the cars we got our engine and/or engine control module from.

Lastly, if our Civic was built between 2001 and 2003, we also need to wire in a relay for the heater unit inside the sensor.

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