Hondata Reflash - RSX Base 2002-2004 MT K20A3

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Reflash your 2002-2004 RSX MT (K20A3 engine) engine computer.

  • Fuel, ignition timing and cam timing optimized.
  • Rev limier optionally increased to 7300 rpm
  • 5-10 HP increase across most of the rev range.
  • 10-12 ft/lb torque increase under 5000 rpm
  • More torque than a stock K20A2 Type S under 6300 rpm. (see dyno graph)
  • No measurable difference in emissions from stock.
  • Fully dealer compatible - works with all Honda scan tools and equipment.

Hondata does not sell direct - all sales and payment must be conducted through Hondata dealers. The ECU reflash form must be sent with your ECU.


  • K20A3-M1: Revised fuel and ignition values with stock rev limit
  • K20A3-M2: Revised fuel and ignition values with 7300 rpm rev limit

Both these reflashes are based on the performance program in the dyno chart below and vary only by rev limit. VTEC point is not altered.

We do not recommend the use of this reflash with nitrous or forced induction. For these applications we recommend the K-Pro.


Within the USA this product is legal only for racing vehicles which may never be used upon a public highway.

EPA/CARB status (USA) Competition vehicles only
Model RSX
Year 2002-2004
Market US
Trim Base
Engine K20A3
Transmission MT
Part Number 37820-PND-A01 to 37820-PBD-A09


This test RSX base model had 28,000 miles at the time of testing. Intake and exhaust were stock. The fuel used was 89 octane - but we recommend 91. We cannot turn your base model into a Type S (please read K series Tech), but we can make significant improvements.

K20A3 RSX base model Stock vs Program

More torque than a stock Type S!

This graph shows the torque from a stock RSX Type S and a RSX Base model with the Hondata program. The Type S had only about 1500 miles and would show more torque after a few thousand more miles.

Comparisons to a cold air intake

Long cold air intakes work the best. The long cold air intake we tested with added 5-6 ft lb across the rev range from 2800 rpm up. By comparison the CAI makes more top end power from about 5500 rpm and up Hondata program makes significantly more torque under 5500 rpm. This graph shows only the CAI with no Hondata program.

In this graph we test the CAI and Hondata program together.


These engines have a VTEC point of 2200 RPM. Under this rpm the K20A3 operates as a 12 valve engine. Hondata does not change this. See K series Tech for more info.

For consistency in dyno testing we suggest you follow the dyno procedure outlined here.


The immobilizer feature on the US Spec RSX is the most advanced to date. The ignition key, the immobilizer box and the ECU are all matched. It there is not a match there will be no fuel or spark. Japanese ECUs have less protection and are more easily bypassed.

The K series ECU, in order to be re-programmed must have a functioning immobilizer system. Three items must be sent to Hondata: the ECU, the ignition key and the immobilizer. The immobilizer works as normal after the ECU has been re-flashed.

Tools needed:

  • Philips screwdriver
  • 10 mm socket and drive
  • Time needed : 10-15 minutes

Removing the immobilizer (Civic Si, RSX / Integra)

Under the steering column remove the three philips screw holding on the bottom plastic cover.

Depress the bottom cover along its top edge where it meets the top cover to separate the plastic clips. Rotating the steering wheel 45 degrees can help.

Lower the steering column and remove the bottom plastic cover from over the height adjustment lever.

Unclip the green connector immobilizer connector and unscrew the securing two philips screws.

RSX ECU removal

The ECU is located in the passenger's footwell. The kick panel is removed after depressing the centers of three small plastic buttons around the front covering panel.

Unplug the three wiring connectors and remove the two front most 10mm locating bolts, plus the rear bolt. The ECU will slide out easily - if it does not, then check that the rear bolt has been loosened or removed.

K20A3 Civic Si ECU removal

The Civic Si's ECU is located in the passenger's footwell behind the glove compartment.

Unclip the lower plastic panel:

Unplug the three ECU connectors.

Remove the lower two 10 mm bolts.

Open the glove compartment and push out from behind the two bump stops. The glove compartment will drop after this is done.

Undo the last 10 mm bolt and slide the ECU down.