Parts Now Pay Later with
Log In Cart
Log In

Create An Account

Log In Cart
Your Cart Is Empty
Free Shipping Over $199.99

Free Shipping Over $199.99

Orders of $199.99 or more ship free within the continental U.S.

Shipping Policy

Hondata 02-04 Honda Civic Si ECU Reflash

Hondata 02-04 Honda Civic Si ECU Reflash-A1
Hondata 02-04 Honda Civic Si ECU Reflash-A2
Hondata 02-04 Honda Civic Si ECU Reflash-A3
Images may be for reference only

Hondata 02-04 Honda Civic Si ECU Reflash

★★★★★ ★★★★★ 6 Reviews
$290.00 & Free Shipping

Reward Points

It pays to shop with K Series Parts and our reward points program! For every $1.00 you spend you earn reward points.

They are easy to earn, just log in to your account when you check out. If you don't have one it is free and easy to setup.

They are easy to use during check out. Click on the "Have Reward Points?" on the shipping and payment selection page.

Reward Point Program Details

You earn 2 points for every $1.00 that you spend.

100 points equal a $1.00 discount.

Maximum discount per order is 5% of the order total.

There is no minimum order total to redeem points.

Points do not apply to shipping or sales tax.

Points are not redeemable for cash.

The point value per dollar, points earned per purchase, and order minimum are subject to change.

Earn 580 reward points. Learn More

Because of the ongoing situation with COVID-19 Hondata is taking at least 2-3 weeks to process ECU's.

Monday-Friday: 9am-4pm MST


The 2002-2004 Honda Civic Si K20A3-Si Hondata reflash program advances the ignition, alters the cam timing and optimizes the fuel for a cold air intake, adding 4-9 ft lb across the rev range.


  • 10-12 Peak HP gain depending on the dyno and modifications
  • 4-9 ft lb torque across the rev range
  • Power peak raised 400 rpm from 6300 rpm to 6700 rpm (higher with headers)
  • Rev limiter raised to 7700 rpm.
  • Fully dealer compatible - works with all Honda scan tools and equipment.
  • 0-60 mph times improved by 1 second.
  • This tune is for 91 octane pump gas
  • Only ECU's with part number 37820-PNF-A01 to 37820-PNF-A12 are able to be reflashed.
  • This program was tuned specifically for a cold air intake
After you order you will receive two emails; one with full instructions on where and how to send your ECU to Hondata and another with the form that you need to sign and include with your ECU.

You are required to send your ECU to Hondata for this service. This product is final sale.

Not legal for sale or use in California on any pollution controlled motor vehicles. See for state by state emissions requirements.

WARNING: This product may contain chemicals known to the State of California to cause cancer or birth defects.


Brand: Hondata
Part Number: K20A3-Si
CARB Approved: No

Vehicle Fitment

Honda Civic
2002 Honda Civic Si Hatchback 2003 Honda Civic Si Hatchback 2004 Honda Civic Si Hatchback

6 Reviews ★★★★★ ★★★★★

★★★★★ ★★★★★
4.83/5.00 Stars out of 6 Reviews
Write a Review
5 Most Recent Read All 6 Reviews
Don't hesitate! Get It!!!!
Dustin | October 29th, 2019
KSERIESParts made the process very simple. Very Fast turn around time. The Reflash is definitely worth the money. Higher revs, Smoother power from 0 to redline. Don't hesitate! Just Get it!!!
in-depth END ALL review
brett | April 17th, 2014
OKAY. soo I got my reflashed ecu from hondata and I couldn't be happier. filled up the tank from empty with 93 (91 is cool too; we have 93 in NY) hooked everything up and let it idle for 10 minutes. at first it was making some noise but it went away once the ecu learned the engine again.. first impressions: -the low end is greatly improved. def pulls harder around the 2000rpm area. when accelerating up to the new redline, it pulls allll the way up to the limiter. -you pass 60 mph before you max out 2nd. and that boring k20a3 now sounds like a proper Si. turnaround time: I paid for 3day from FedEx. shipped it on a saturday night and my parents signed for it on wednesday while I was away. that is QUICK. hondata gets an A+ for quickness the reflash gets an A+ for making the ep3 feel more fun to drive like an em1 gets an A+++ for handling the transaction the BEST $300-340 (depending on method of shipping) you can spend with an oppurtunity to get kpro down the road stock k20a3 with a injen SRI
Re_flash kicks azz
Sergio | February 7th, 2012
Just got my reflash. Dam this runs good now. Love those higher rpms. Has a hell alot more top end. I totaly recomend it. Pulls harder than my brothers 09 si.
Reflash was ok, but CRSX is BEYOND excellent..
William Chu | May 11th, 2011
The reflash was decent... I didn't think it was that great of a gain. On the other hand, I love CRSX. Best service! Very prompt and easy to deal with. Never had a problem buy anything from here. a "B" for reflash but definitely an "A++" for CRSX.
Crazy Gains
Dustin | April 23rd, 2011
This is exactly what the EP3 needs your crazy if you don't do this and shipping is so fast I sent the ecu on Tuesday at about 4:00 from Indiana and had it back Thursday at 1:00. Great purchase I love it.
Read All 6 Reviews