Repair PGM-FI ECU Goldwing
GL1800 2001 to 2005
Pre-amble:
Often Honda changes part numbers when they change model years without any discernible variances at all in the function. You will note that I have written summations (Goldwingfacts.com, and on my site, under Repairs menu) about that part number change with the ABS controllers, prior to 2006 and 2006+ years. I chased the schematics on those modules and concluded that that they cross over directly, and that has been borne out, several times.
As these great ladies age, Honda stops carrying inventory on parts, those parts they have begin to increase in cost (radically: 15 years ago the $2000 ECU was $525 average) or become totally unavailable.
With that considered I decided to review the ECU PGM FI units for the years 2001 to 2005 to check for cross-over viability.
PGM-FI ECU: Honda Goldwing GL1800 and GL1800A Part Numbers:
2001 2002 2003 38770-MCA-P00 or 38770-MCA-A00 or 38770-MCA-A01
2004 38770-MCA-A21 or 2005 38770-MCA-A41
NOTE: There is no difference in PGM-Fi units for NON-ABS-equipped GL1800’s and the ABS equipped GL1800A.
The Honda Service manual shows for ’01 to 03 (with three different part numbers) as being the same schematics, as do the ’04 and ’05 years (with two different part numbers).
Having traced all necessary elements of the schematics for ’01 to ’03 years, and compared that to all comparable elements of the ’04 to 05 years, I have surmised, after tracing then re-tracing each and every wire for certainty, the following.
The additions (changes) to the schematics and hence the wiring from/to the ECU, boils down to the simple fact that Honda increased the data-link connector plug (under the seat by the relay box) from 2 pins (“service connector”) to 4 pins (“data-link connector”) in 2004. That allows them to read more engine data for computer diagnosis.
The variances are thus:
There is changed and additional pin use in the ’04-‘05 years in the:
22 Pin BLACK connector input:
The ground wires on “LG” and “PG1” and “PG2” (Black 22 pin, via G(reen) wire) go to ground differently: which means nothing: they go to ground, regardless of the path.
The “IGP”: That used to go directly to the PAIR sensor (via Bl/Y wire), after branching to the right hand O2 sensor. They added another branch to go to one of the additional pins on the data-read plug in ’04.
22 Pin GRAY connector input:
The “RXT-TXD” line: Not used on the prior years, on the ’04-05 it goes directly to (via O/w wire) the data-link plug.
The “IMOV” line was not used on prior years, although it is on the schematics and ECU. After ’03 it was put into use by branching into the same line as the “IGP” line (same Bl/Y wire) above: an additional branch to the PAIR sensor on the same wire, and also feeding to the data-link plug.
Data-Link Usage
Data-link connection plugs in the Goldwing are for diagnostic purposes. They are not used to re-map the firmware in the ECM because they are not ‘re-map-able’.
Hence, that plug is read-only, and should have nothing whatsoever to do with the operation of the ECU, hence of the motor operation.
The ECU is just that: Engine Control Unit. Lines coming from the module enabling it to be plugged in to a computer are rarely if ever used (unless you are a dealer and have the computer software to do so) unless to reset the ECU, which is easier to do by simply disconnecting the battery for a while, then starting it without touching the throttle until it has gone through a cycle of radiator fans-on-fans-off: a thorough warming to allow the ECU to reset. In 20 years and dozens of 1800’s I’ve never used it except to remove locked in F1 Codes.
Summary:
In conclusion, I believe that the ’01 to 03 ECU should work just fine in the ’04-‘05 years, with two unused ‘pins’ and one that just doesn’t have the diversion that the ‘04+ has. I would bet on it.
In that I don’t have, unfortunately, an ’04 or ’05 in the stable (I only have 2 ‘01’s, and 2 ‘03’s, an ‘06 and an ’07), I cannot prove out the theory. If I did, I would.
Subsequent to the above, I found a note from a member of GL1800 Riders who stated that he had verified the cross-over between the ’03, ’04 and ’05 ECU’s. Hence that is applicable to 01 through 05. He erred in stating that the wiring was the same, as it is not quite, as per the above. However, the proof is in the pudding: actual cross-over testing.
What will definitely NOT fit the first-gen GL1800:
After 2005, in (second gen) 2006 and later: they completely redesigned the PGM-Fi unit pin positions and changed the pin designations. There is no chance to have it fit or make it fit the earlier years.