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OBD-1 ECU Transistor Checking
Author _ Katman | Created_ June 2005
VTEC Transistor


This article is designed to help explain how to identify OBD-1 1720 & 11F0 boards for VTEC and Auto/Manual transmission.


So, you're on the prowl for a reprogrammed P28 ecu and you find some fella selling one on Honda-tech. You pay the guy and he ships you the P28. You receive it and there's no part number sticker on the side of the ecu casing - you scratch your head and think that's a little odd. You then go plug the ecu into your car all happy as hell, turn the car on and rip down the street like your late to work - but something's wrong - VTEC doesn't kick on at all. So, you go rip around town a little more just to make sure VTEC isn't working. It never kicks on. You're not 100% sure but you realize and lose faith in this ecu thinking its NOT A P28. You go back home and plug your stock ecu back in just to make sure VTEC works....and it does. You then email the chap who sold you this supposed chipped P28 ecu and give him a piece of your mind; depending on how the seller is he'll either take the ecu back, refund you, or send you the right ec, or bicker back & forth saying it definitely is a P28...blah! blah! blah!

Well, here's the only article on the internet (I assume) that will show you how to tell a P28 from a non-P28 so this kind of scenerio doesn't happen to you!


First off, this article is only covering these OBD-1 civic and integra ECU's:

P05 / P06 / PR4 / P28 / P74 / P61 / P91

Normally, when an ecu hasn't been tampered with, a person can simply look at the side of the ecu casing for the factory part number sticker as seen in [Fig.1]; and go off this as to what type of ecu it is. Sometimes (and this is rare) a devious jackass takes this sticker off or they swap out the internals (such as putting in a non-vtec main board into a VTEC casing) with parts that are not what the specified part number sticker is intended to be and pawn it off to some poor unknowing soul....or a scenerio thereof.

What you want to do is remove the top cover of your ecu and look for the board number which is seen in [Fig.2].

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(11F0 for short) and 02D01720-1500 (1720 for short) are the most widley used Honda OBD-1 ecu's around. They're used in almost every SOHC & DOHC VTEC & NON-VTEC OBD1 vehicles, with exception to some LS and all GSR vehicles. These two boards are different in many ways but are similar when it comes to specific transistors which is the heart of this article.

There is a third type of OBD-1 ecu that Honda uses known as the 02D01980-1502 board (1980 for short). This board is only found in the OBD-1 P75 (LS) and all P72 (GSR) ecu's. See [Fig.3]. The 1980 board is a totally different layout vs. the 11F0 & 1720 boards and is easily distinguishable if you compare the transistor location as I have in [Fig.4]. We're going to ignore the 1980 board.

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Now here's where you wanna pay close attention.

Both 1720 & 11F0 boards use these " transistor lots" or "trans-lots" as I like to call them.
Each trans-lot has a designated ID number: IC13, IC14, IC15, and IC16.

IC14 & IC13 are both VTEC trans-lots which control the on & off switching of the VTEC solenoid.
IC15 & IC16 are both auto-transmission trans-lots which control auto tranny related solenoid(s).

shows what a non-VTEC 5-speed ecu trans-lots look like - totally empty.
[Fig.6] shows what a non-VTEC Auto ecu trans-lots look like - IC15 & IC16 are filled.
[Fig.7] shows one version of what a VTEC 5-speed ecu trans-lots would look like - only IC14 is filled.
[Fig.8] shows another version of what a VTEC 5-speed ecu trans-lots would look like - IC14 and IC13 are filled.
[Fig.9] shows what a VTEC AUTO ecu trans-lots would look like -all IC lots are filled.

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A dead giveway for an OBD-1 DOHC VTEC B-series ecu is the knock sensor board as seen in [Fig.10]. You'll find the knock board on a US P30, P61, P72 ecu's.

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So there you have it!

By having a trained eye, the transistors and knock sensor board can be a dead ringers in helping one distinguish a type of OBD-1 between a non-vtec/vtec and auto/5-speed ecu's no matter what part number sticker is on the side of the ecu casing (or not).

The information in this article applies to:

  • 92-95 OBD-1 civic CX/DX/Si and delsol ecu's - excluding civic VX
  • 92-95 integra ecu's excluding some LS integra's (P75 ecu equipped) and all B18C1 GSR integra's