Shavelieva

History:
Working on my sister in laws 1998 Honda Accord EX(not leather) LEV - non-California emissions car to pass emissions for Tennessee.

About two years ago she bought it, had the ECU replaced shortly after by a honda mechanic because it died, or needed to be replaced, or something. Car ran fine.

Back in the summer last year she came back with a CEL, p1166/p1167. I've looked at it off and on as well as the previously mentioned honda tech since then evey couple of months. At first I gave a go with replacing the Primary and secondary A/F/O2 sensors with Autozone/Advance/Oriley's. After nothing changed and they kept coming back, decided to check out wiring for voltage, continuity, etc. I'll mention I thought everything was ok at this point since there was "a" voltage coming from pins 3 & 4 of the harness and because I was aware of the ECU providing the voltage i assumed(thinking the ecu would be smart enough to turn it up once resistance was detected) it would be less if no sensor was attached... Regardless I moved on and figured the honda tech would figure it out. Sensors ended up getting returned to parts stores and he had her buy OEM sensors from Honda dealership($200 primary, i forget what the secondary one cost). Magically nothing changed.

I decided to start looking at it again and decided to look at the ECU since he recommended replacing it since the OE sensors did nothing. I was thingking maybe something was just fried and could be replaced or something came loose.

WTF:
I give some info on the car for validation as if the prior wasn't enough
VIN: 1HGCG5654WA204569
1998, 4-Door, Automatic, not leather, KA-Emissions not California ULEV, just LEV.
So I pull out the ECU under the console between the floorboards to get the model, L... why's there an L in the model? must be because the LEV emmisions rating...
pic for proof of what I pulled out


37820-PAA-L73

Look up prices on eBay
37820-PAA-L73 | eBay
Not too bad, its 15+ yr old car, can't expect them to be too much. by generation you expect some cross-over in parts 98-02 runs the gambit for this gen. Looking over some of the listing more closely some were pulled from California cars, some say California emissions ONLY... Odd, since this isn't a California car but hey maybe all is well once you program the VIN, year, etc when you're setting the immobilizer...

So I look into it some more and start questioning what is a valid ecu for this particular model. Most Honda parts site just list 37820-PAA-407 as the OEM part and obviously from these guys prices are $300-$1500, but their reference resources are invaluable so its hard to harp on them too much.

Honda's eParts shop is usually good
https://estore.honda.com/honda/parts...++1310&dl=#003 they list it as 37820-PAA-407

Honda Parts Now is nice beacuse they typically show a replacement model if such exists
37820-PAA-407 - Honda Parts Now again listed only as 37820-PAA-407

so lookup on eBay 37820-paa-407 | eBay Ouch, $200-300, but that's what OEM part numbers get you I guess.

If 37820-PAA-407 is the OE part then are there any alternate part numbers? Searching eBay & the like based on the model/trim varies site to site, by VIN you only get the aforementioned model. Either way 37820-PAA-L71 or any variant of the Region L doesn't seem to come up. The L designation appears to be a California emissions rating.<-correct me if this is incorrect).

ECU:
the way I read the ECU model/honda
37820- general Honda Part numberin reference the the Control Unit(Cabin) aka ECU.
PAA- is some sort mystery of a designation to the Model, Trim, engine(correct this someone).
L,A,J,E,C-3rd to last Letter/number is a region identifier L-California, A-Amurka, J-Japan, E-Europe, C-Canada, wonder what the phillipines/Australia get?
0,1,5,7- 2nd to las letter is a Transmission designation, still not clear for sure.
last digit- ECU specific revision ID, to represent manufacturer changes.

So what really makes a California ECU(ULEV)(L) different than an LEV(A,J,C,4) version? Turning back to the FSM http://www.gvrdeu.org/Honda%20FSM/Ac...ccord%20SM.pdf for the 98-02 Accord wiring diagram(starts on 11-13, Page289), there is a difference not only in where the sensors are wired, but how the heaters are powered.

Ignition switch at levels IG1(I), and assumably IG2(II), IG3(III) power(+) is applied to fuse(8) No.6 ECU(ECM/PCM)/CruiseControl(15A)
Flow continues to Rail "E"
Rail "E" powers
EVAP canister purge valve
Engine mount control solenoid valve
EVAP Bypass solenoid valve
EVAP canister vent shut valve
vtec solenoid valve
the above are railed on the right side of the wiring diagram on page 290(11-14). On the right side you will see another rail "E" bridging:
Primary HO2S(Sensor 1)*5 completing on ECU C1 - PO2SHTC *5
Secondary HO2S (Sensor 2) completing on ECU C16 - PHO2S *5

This is one scenario. The next page dictates an alternate scheme...

an alternate Rail "E" on page 11-15 page 291...
A/F Sensor Heated Control Relay *3....WHat? Relay, I've not seen any relay for the O2 sensor, but then again I thought maybe that explains the low voltage.... So I hunt and look and supposedly a 98 accord o2 sensor relay should exist to the bottom right side by the door under the dash beside another relay. Its not there however, so back tot he books and confirmation that the relay exists on the California/Canada model. Continuing through the diagram, voltage via the ignition comes to the relay which is further potted to the B16 P02SHTCTR*something... so there's one difference in the ECUs...

The relay would then, dependent to the ECU potting the voltage from the ignition switch on or off the "F" rail which bridges to the A/F Sensor(Sensor 1)*3 which is directly connected to the ECU via
C13 - PO2SHTC+ *3
B19 PO2SHTC *3

So the wiring is similar but different, I guess with the ULEV California standard the ECU controls the relay to turn the Heater located within the Primary O2 sensor off once it has reached "operating temperature" since it may cool in stalled traffic, think Interstate5, at super low idle. I would also think it would be good to let the sensor cool off as SULEV, PZEV, etc sensors are way more expensive and to increase its longevity(just a thought). Either way with this new info, testing away sure enough this a a California ECU through and through...

So are there any alternative part numbers to the OE 37820-PAA-407? I've not found a definitive guide on the ECU naming scheme and I would think someone would have made a breakout of cross-compatible ECUs or something from Honda would've "leaked" as a cross-reference.

Shavelieva

So looking on Bernardi's
Find Honda Parts and Honda Accessories by Car Model - Bernardi Parts
It actually lists 3x different model ECU(Cabin)
37820-P8C-305 | Honda ECU - Bernardi Parts
37820-PAA-407 | Honda ECU - Bernardi Parts
37820-PAB-307 | Honda ECU - Bernardi Parts

So that's something better to go off of. Would still be nice to see a cross compatible list for reference.

EDIT: I may try to turn this post into an interchange of part numbers

37820-B8C-

37820-PAA-

37820-PAB-A60

37820-

Shavelieva

Found this in regards to Honda Motorcycles, I wonder how much of it translates to their automotive Division?

General parts:

XXXXX - XXX - XXX(XX)
Function Number

XXXXX - XXX - XXX(XX)
Component Number

XXXXX - XXX - XXX(XX)
Parts Classification Number
(These numbers relate to the Product Code of the first Honda motorcycle model to use a particular part; if the same part is subsequently used on another model, the Parts Classification Number generally remains unchanged. Some of these numbers are listed here. For more information, see the Parts Interchange Info page.)

XXXXX - XXX - XXX(XX)
Modification Designation

XXXXX - XXX - XXX(XX)
Subcontractor Designation

XXXXX - XXX - XXX(XX)
Color Code (if any)
(Part number color codes do not necessarily correspond to the Honda motorcycle paint codes listed here; they are keyed to the Honda paint codes listed in the relevant Description section of the Parts Catalog.)

Source


And according to Relic1 post he seems to confirm my understanding of the model designation.


This is also a good source of model designation, too bad its info only on Civics and dated.
https://www.hondata.com/vehicles.html
https://www.hondata.com/ecus.html
https://www.hondata.com/techecuid.html

Shavelieva

ECU 37820-PAA-A51 fixed all issues.