Which ECU can be swapped
Question regarding DSM ECU
ECU Identification Chart
Identifying your ECU
ECU Generations
ECU Part Numbers


Question regarding which ECU can be swapped:


· Can we swap all ECU?
· Which ECU can be swapped?
· What other modification needed?

OBD2 to OBD1 conversion on 97+ Honda Prelude

Some things to consider when doing this modification
The ECU is larger, so you need to modify the ECU holder.

Distributor wiring You need to re-wire for the distributor. The TDC and CKP sensors are located at the crank on the 97+ Prelude. On the OBD1 Prelude, these sensors are located in the distributor. This is why you cannot alter timing on a 97+ Prelude. You need to re-wire these sensors, so that the ECU reads them from the distributor. The wiring is as follows: (coming soon...)

Question regarding DSM ECU:

· Can we chip all DSM ECU?
· Which year model has EPROM?
· How can we tell from the ECU cover?

The key for hunting down EPROMs after *1990* is to look for an 'E' in the lower right corner of the label on the top (not the sides). Yes, it is that easy. If you have an 'M' or 'T', you are out of luck. For 1990, you have to open up the ECU. There is no correlation between build dates or models or anything else that I've been able to absolutely verify.
Be careful of rebuilt ECUs. The rebuilders that I know of do a good job of fixing the ECUs, but sometimes, they get the topcovers mixed up. The only way to know for CERTAIN that an ECU has an EPROM is to just open it up.

BTW, part numbers mean nothing. I've seen the same Mitsu part number on an EPROM ECU as a non-EPROM ECU...

In 1990, they have different code revs for CA smog and Fed smog. They also have no E/M markings on the ECU case. Possibility that all CA cars have EPROMs due to low run amount compared to Federal cars? Possibility that all 1990 cars have EPROMs (since none are marked)?

In 1991, code is tightened considerably, table sizes are reduced, and they are able to squeeze all versions of the turbo code into one ECU. First ECUs to be marked with E/M. Definitely a LOT of non-EPROM ECUs, but a lot of EPROM ECUs are also out there.
In 1992, there are no code changes made. Possible that there are no 1992 cars with EPROMs?

In 1993, code is changed to meet new regulations on fuel vapor recovery. New code generally means EPROMs are available (at least until 1996).

In 1994, code is changed for minor smog enhancements (probably). Also, all cars made from this year forth carry CA smog equipment (meaning a better EGR system).

In 1995, code goes through 5 running changes during the year as Mitsu engineers struggle to get OBDII right (I'm guessing). First three revs of code appear to be AWD only (no speed limiter). Likely that there are nothing but EPROMs in this year?

I have never gotten a 1996 ECU to modify, so I suspect that there is not an EPROM available at all in this year? Probable that a 95 ECU will run a 96 car, though.

I have a 1997 ECU. It is marked with a 'T'. No EPROMs this year that I know of?

1998 and 1999 are suspected to be a radically different ECU. I do not have one on hand, nor have ever seen one. I'm certain that there are no EPROM ECUs available after 1996.
Galant GVR-4s are a special case. They have always idled at a slightly higher speed and had different variables due to different gearing. Some even had a slightly different MAF. Anyhow, their low volume GUARENTEES EPROM availability.

Identifying your ECU

To identify your ECU you will need to know its generation, part number and possibly its ROM number.

The ECU can be located in several places: under a metal plate in the passenger's footwell (models up to 91), in the passenger's footwell behind a plastic panel (models 92-99) or by the driver's footwell under a plastic panel (some models 2000+)

The computer is connected via three connectors that pull out when a plastic clip is pressed. Remove the computer, and with a philips screwdriver remove the metal lid from the top of the computer. There may be small daughter circuit board covering some of the main circuitry. Unscrew this and lift it out of the way.

ECU Generations

Honda ECUs run in generations, which use different connectors.  Below is a stack of ECUs running from the newest generation at the top to the oldest generation at the bottom.


ECU Part Numbers

All Honda ECUs have a part number which is located on the side of the ECU and inside the ECU on the connector. e.g. 37820-P72-A01

The part number consists of three components:

  • Honda's part number for ECU, which is always 37820
  • Three characters (which are loosely related to the model of car/engine). e.g P72
  • Three characters (which are the revision of the ECU) e.g. A01

The middle three characters are the most useful to identify what the ECU is.  Different generation ECUs may use the same characters. e.g. a P72 OBD I ECU is different from a P72 OBD II ECU. Here is a list of common ECUs: 

  • PG6 : 88-89 Integra (all makes)
  • PM5 : 88-91 Civic/CRX DX
  • PM6 : 88-91 Civic/CRX SOHC Si
  • PM7 : 89-91 DOHC ZC (JDM 'EF' ECU)
  • PM8 : 88-91 CRX HF
  • PR2 : 89-91 ZC (Euro)
  • PR3 : 89-91 JDM B16A EF8/9
  • PR3 -J00 or J51 : 92 JDM Integra B16A EF8/9
  • PW0 : 89-91 JDM B16A EF8/9 DA6-XSi
  • PR4 : 90-91 Integra LS/GS
  • PS9 : 88-91 4 door Civic EX Auto
  • P05 : 92-95 OBD-1 Civic CX
  • P06 : 92-95 OBD-1 Civic DX
  • P07 : 92-95 OBD-1 Civic VX
  • P08 : 92-95 OBD-1 Civic D15 JDM
  • P0A : 94-95 OBD-1 Accord EX
  • P13 : 93-95 OBD-1 Prelude Vtec
  • P14 : 93-95 OBD-1 Prelude Si (non Vtec)
  • P27 : 92-95 OBD-1 EG JDM Civic 1600 sohc
  • P28 : 92-95 OBD-1 Civic Si/Ex
  • P30 : 92-95 OBD-1 DelSol DOHC Vtec Si/EG SiR
  • P54-G31 : 1997 Honda Accord 1.8 LS
  • P61 : 92-93 OBD-1 Integra GSR
  • P72 : 94-95 OBD-1 Integra GSR
  • P72 : 96-00 OBD-2 Integra GSR
  • P73 : 96-00 OBD-2 Integra Type-R (JDM & USDM)
  • P74/75: 92-95 OBD-1 Integra LS/GS
  • P75 : 96-00 OBD-2 Integra LS/GS
  • P2N : 96+ OBD-2 Civic HX Coupe
  • P2P : 96+ OBD-2 Civic EX Coupe
  • P2E : 96+ OBD-2 Civic DX Coupe
  • P2M : 96+ OBD-2 NZ Civic SOHC VTEC
  • P2T : 99+ OBD-? Civic Si Coupe
  • P5P : 97-00 OBD-2 Prelude Type-S (JDM ECU)
  • PBA : 97+ US Acura 1.6EL
  • PCT : 98+ JDM ITR / CTR
  • PCX : 99+ OBD-? S2000