Hondata Reflash - Civic Si 2002-2004

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Reflash your 2002-2004 Civic Si engine computer.

  • Fuel, ignition timing and cam timing optimized.
  • Rev limiter raised to 7700rpm.
  • 10-12 peak hp gain depending on the dyno and modifications
  • 4-9ft lb torque across the rev range
  • Power peak raised 400 rpm from 6300 rpm to 6700 rpm (higher with headers)
  • 0-60 mph times improved by 1 second.
  • Fully dealer compatible -works with all Honda scan tools and equipment.

This is for an ECU reflash - the ECU is not included.  Hondata does not sell direct - the reflash must be purchased from a Hondata dealer. The ECU reflash form must be sent with your ECU.

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

We recommend that 91 octane fuel be used with this reflash.


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

Sales Region US
EPA/CARB status (USA) Competition vehicles only
Model Civic
Year 2002-2005
Market US
Trim Si
Engine K20A3
Transmission MT
Part Number 37820-PNF-A01 to 37820-PNF-A12


2002 Civic Si, stock and with K20A3-Si Flash program.

Tuning notes

This tune is for 91 octane pump gas. The reflash has not been tested with 87 octane fuel. In the graph above, the change in octane was worth about 2hp and the tuning 8-10.

We recommend that 91 octane fuel be used with this reflash.

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

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.