Hondata Reflash - TSX 2004-2005 TSX MT/AT K24A2

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Reflash your 2004-2005 TSX engine computer.

  • 5000 rpm VTEC point decreased from 6000 rpm
  • 7600 rpm Rev limit, increased from 7300 rpm (for auto trans must be in sportshift mode)
  • Maximum torque gain 26 ft/lbs torque at 6000 rpm
  • Maximum power gain 29 hp at 6000 rpm
  • Peak torque increases from 169ft/lbs at 4500 rpm to 175 ft pounds at 7500 rpm
  • Peak power increases from 206 hp at 7100 rpm to 210 at 6800 rpm
  • Very wide flat smooth torque curve. 90% of peak torque available from 2000-7000 rpm.
  • Fully dealer compatible - works with all Honda scan tools and equipment
  • California emissions legal (CARB EO D-742)

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.

The Hondata TSX reflash is designed for use with an intake and headers. It will work very well with a stock airbox and stock headers. Testing was done with a stock cat back system.

How do I remove my ECU and immobilizer?

The ECU is located behind plastic panels to the right of the driver's right foot and the left of the passenger's left foot. Both panels will need to be removed. You will need a Philips screwdriver and 10mm socket. Complete removal instructions are to be found on this page. Alternatively you may download and print out the TSX ECU removal pdf file(300k).

Driving Impressions

This reflash is difficult to feel because it keeps the torque delivery flat and smooth to a much higher RPM. Rather than the torque dropping 20 ft/pounds from 5000 rpm to 6000 rpm stock, the reflash keeps the torque drop to only 10 ft pounds between 5000 and 7000 rpm. VTEC transition at 5000 rpm is also very smooth with only a slight change in induction noise.

Sales Region US
EPA/CARB status (USA) CARB EO D-742
Model TSX
Year 2004-2005
Market US
Engine K24
Transmission MT/AT
Part Number 37820-RBB-A02 (04 MT TSX)
37820-RBB-A03 (05 MT TSX)
37820-RBB-A54 (04 AT TSX)
37820-RBB-A55 (05 AT TSX)


Results for Manual Transmission TSX with no modifications

  • Red Line - Stock ECU
  • Green Line - Reflashed ECU

Click to enlarge picture

Results for Manual Transmission TSX with intake and header

  • Red Line - Stock ECU with intake and header
  • Green Line - Reflashed ECU with intake and header

Click to enlarge picture

Results for Auto Transmission TSX

  • Green line - Completely stock low milage (300 miles) Auto TSX
  • Pink line - Completely stock low milage (300 miles) Auto TSX with Hondata Reflash

The gearbox shift points have not been changed. To use the higher rev limit you must be in sportshift mode.

Click to enlarge picture

In depth analysis for Manual transmission TSX

Lets look at a typical power run. With the stock ECU you change gear at the redline and drop around 2000 rpm onto the lowcam. Average the power readings over this range and you get 182 hp.

With the Hondata TSX reflash your shift point is 300 rpm higher and you drop in the rev range to just before the torque peak while remaining on the high cam. Average power is about 201 hp in the marked power band. This is an average increase of 19 HP from stock, even though the peak power difference is only a few HP, the area under the curve is substantially better.

Click to enlarge picture

Comparison to stock for Manual transmission TSX

This compares the dyno plots above to the TSX 6 months ago when it only had about 1000 miles (dotted pink run). With more miles on the car, the difference in base power would have been higher.

Click to enlarge picture

The TSX uses adaptive knock control. This means it will listen to the knock sensor and advance or retard the timing appropriately. This is good as it means the TSX will readily adapt to higher octane fuel and add a couple of degrees ignition advance. The TSX ECU only takes 3 or 4 power runs to adapt, and is constantly relearning. Unfortunately the side effect is that successive power runs can vary by up to 4-5 ft pounds of torque due to engine noise or knocking that is inaudible to the ear. If your coolant temperatures are too hot (>195 F) or the engine is hot from dyno runs, the ECU has a tendency to retard the timing.

All NA K24 engines we have tuned drop sharply in torque after 6000 rpm - even the 270 hp full race engines. This is a function of the long stroke of the K24 engine. The best way to change the shape of the torque curve is to improve the cylinder filling above 6000 rpm with forced induction - such as supercharging in this comparison with a supercharged K20A3 Civic

The intakes on the K series engines get very hot. They have a metal intake gasket which transfers heat from the head very quickly and are heated by hot air from sitting right behind right the radiator . Pay lots of attention to keeping everything cool and you will see results. The K24 Hondata intake gasket reduces intake temps about 15-40 degrees F. Use a cold air intake where possible.

These instructions document the removal of the TSX ECU, and immobiliser for reflashing by Hondata. The TSX ECU is located between the driver's and passenger's footwell.

Tools needed: Screwdriver, ratchet and 10mm socket.


By the drivers right foot there is a triangular plastic panel. Hold the outer plastic ring with one hand and turn the center plastic Philips screw 1/8th of a turn counterclockwise with the other. The plastic Philips screw should then be easily pulled straight out.


From the top section of the triangular panel, remove the metal Philips screw.


The panel is secured by three spring clip fittings located as shown here.


Pull the plastic panel out.


Pull back the carpet and undo the left 10mm bolt holding in the ECU.


Repeat for the right hand triangular kick panel.


It is secured by only one plastic Philips screw.


The three spring clip fittings are located here as shown.


Unclip the 4 ECU connectors. The clip to depress is located on the top middle of each of the 4 ECU connectors.


Unbolt the second of the two 10mm bolts securing the ECU.


Slide the ECU out. It is quite a tight fit.


Insert the ignition key and turn the steering wheel to the left by about 45 degrees. Depress the top plastic in at the centre by about 3mm. This is to clear a clip located on the bottom piece of plastic. There are three clips on the left hand side. And three on the right.


Rotate the steering wheel to the right and repeat.


The location and structure of the three right hand clips from outside.


And from inside.

Remove the three screws holding the bottom piece of steering column cover on.


Lower the bottom steering wheel adjustment arm. You will need to move the steering column in and out as well as up and down to remove the lower piece of plastic.


The immobilizer transceiver is the circular plastic ring closest to the head of the ignition key. It is held on by two screws.

Make sure you have an unworn correctly sized Philips screwdriver as you do not want to burr the heads on these screws.

The three items needed to be sent are one key, the immobilizer and the ECU.


Transfer these serial numbers onto the reflash form and send to your dealer.