Hello,
Hope I知 posting in the right place. I知 wondering if I am looking at a failed ECU. While visiting family, I am trying to help my nephew with a fuse 44 blowing problem that occurred as he was driving. Fuse does not blow with connector A unplugged from ECU (PCM?). But, no harness pinouts that I can find match what is in his car (1998 Civic DX w/ auto trans) to help trace possible wiring problems. ECU module is 37820-P2E-L82. Regardless of version, harness views seem to show pin 1 at top left (looking into the connector, I hope). Given this, I have Pwr in from the Main relay to pins 1,9,10,12. Pins 2,3,13,14 connect to chassis ground.

Inspection of ECU circuit board verifies that pins 1+12 are connected as well as 2+13 and 3+14. Logical enough, as these pins are in line. But, testing indicates that the power pair 1-9 is directly connected to ground pair 3-14. The board looks fine (as well as the wiring harness and visible wiring under the hood) but this measurement would seem to indicate a failed transistor that should only connect something to ground when turned on. At any rate, I致e never seen a working PCB that had voltage and ground directly connected. I hate troubleshooting by substitution but this module seems to be available on Ebay for $50.

In case the ECU was fried by a failed component I'd sure like to get a correct pinout to see what's hooked up to connector A so I don't have to return with wire tracers, probes, etc.

Any thoughts?

Thanks,
jvf

 

Sounds like you have a good reason to believe the ECU is bad with the unplugged ECU connector A test.

 

Thanks RonJ,

I’m starting to think we should order the ECU. Even at 50 cents/hr for me to start removing and testing PCB components, we’d be ahead of the game. Your posted diagram illustrates my other dilemma. Unless I’m reading these diagrams incorrectly, A1-A4 are shown as being connected to the ECU. Your diagram shows +12v being common so the ECU would switch ground. But-Our A1 goes to +12v at the main relay, A2and A3 are grounded and A4 doesn’t even have a wire connected. ???????????????????? They said this car came from Canada but I don’t see what difference that might make.

jvf

 

A1-A4 are grounds for the fuel injectors. Post pics of the wires you're testing.

Pins A11 and A24 are often the sources of ECU shorts that blow fuse 44.

Canada and U.S. should be the same.

Has somebody been doing electrical work on the car?

 

Hi RonJ,

Will send pics later, they’ve got me working on another project today. I’ve been suspicious that I have the pinout numbering “backwards” and tried to test “in reverse” to see where the four injector pins were in order to get oriented. But, without my good test probes and doing it myself (of course nephew was unavailable) I was having trouble making connections on both ends at once. I’ll collar him and we’ll test to find A1 then take some pictures.
jvf

 

Fuse 44 also powers the IAC valve and heated 02 sensor(s), unplug then first and see if fuse still blows.

Question, when does the fuse blow, as soon as you put it in or when you turn on the ign.? 94

 

Hello all,

Things are starting to make sense so possibly no pictures needed yet. With the help of someone sticking a paper clip into the injector connector and holding the test probe to the clip along with me at the other end probing with a sewing needle pinched to the other test lead, I have found pin 1 (# 4 injector). So, looking into the connector, this makes pin #1 at the top right and looking into the ECU makes pin #1 at the top left. I guess I should have been more insistent to know where pin #1 was on the connector looking in.

Unfortunately, this does not change the measurements at the ECU itself. Pins 11+24 (IGP1 and 2) are shorted to logic grounds 9 and 22. So, I still think the brain is fried.

So, it is the chicken and egg question again. Did the ECU get fried because of an external or internal failure? The car conked out amid some smoke under the hood and a bulging battery. I’m thinking the regulator gave out with over voltage boiling the battery and possibly spiking the ECU so I’ll need to check the regulator as well.

Other readings at the harness show gnds at pins 5+6 (O2 sensor stuff), 18 (MIL) and 29 (Evap valve) this seems normal but I’ll unplug stuff check these again. Power from Main Relay #3 also shows up at pins 13+14 so I need to see if this is going through the IACVN for pin 13. As for pin 14, diagram says IACV positive side but I’m not sure of what that means. If pin 14 is supposed to send power this might be a short somewhere. Either way I’ll find these items (I hope) disconnect wires and check the harness again.

fcm-fuse blows when turning to start position. After some more prodding, will put everything back together with IAC valve and sensors unplugged and try it (we have plenty of fuses for testing) but I’m still nervous about the IGP pins shorted to logic ground.

Thanks,
jvf

 

P.S—forgot to ask the obvious. Do any of you have a module lying around? If so, could you check continuity between pins 11-9 and 24-22. Any combination should work as 11 and 24 are common on the PCB board as well as 9+22.

Thanks

 

IGP 1 & 2 will show a ground unless ign. on, what you see is the ground on the other side of all the other loads, [injectors, IAC valve, 02 sensors]. 94

 

Always verify your connector pin outs using wire colors.

And the service manual tells you how to interpret connector pin outs:

 

Hello RonJ,

Thanks for the excellent diagrams. I have been cast into this flying blind with only a cheap Haynes book from NAPA and dubious web information (I hate it when that happens). If they keep this car, I’ll buy the service manuals myself if I have to.

BUT---we are achieving success! (Sort of-at least we aren’t blowing fuse 44 anymore). Fortunately, even on Maui, these cute little rice burners elicit a following (I’m an old school V8 guy with a 1982 Mustang converted to mass air FI). We hooked up with a friend of my brother in law who races them at the strip. He had a couple of ECU modules, one of which was correct for the manual transmission version of this car. I tested them both for shorts between pins 9 and 11. Neither had continuity confirming that our ECU was indeed toast. I figured the manual transmission ECU would start the car at least so I plugged it in and it fired right up. We shut it down immediately while I got the multimeter to check alternator output for excessive voltage. Subsequent attempts to start failed but it’s been sitting for several weeks with a weak battery so I’m hoping we’re just at the “get it full of fuel and spark” phase. Meantime, our friend has located the correct ECU and we’ll get it this weekend.

One thing seems amiss, though. Unless my nephew was manipulating the key incorrectly, the fuel pump didn’t run in the ON position for a couple of seconds while pressurizing the system. I only heard it run when trying to start. If this is indeed the case and I can’t figure it out, I’ll search the forum and start a new thread if necessary. Thanks for your help.

Regards,
jvf

 

If the system pressurized, then the pump primed.

Sounds like you're making progress.

I'll PM you a link where you can download the service manual.

 

Hi RonJ,

We’re running! Thanks for hanging in there and helping with wiring info because I was pretty lost for awhile. I bounced the car up and down doing the old “shake your tail feathers” dance and, contrary to popular belief, determined we had no fuel in the tank. Fortunately, they had a gas can with about a gallon and a half so we didn’t have to go and get fuel. I had charged up the battery and after the fuel rail primed, she started right up with the manual transmission brain (our friend spaced out and didn’t get the auto trans brain but promises it soon). I believe my original diagnosis was correct. As it started, I monitored voltage across the battery and when the alternator kicked in, the voltage started rising. We shut down when the voltage went past 16v and still rising fast. So, I think that cooked the other battery and probably fried the brain as well. I want to change just the regulator but uncle says replace the whole thing.

You asked earlier if others had worked on the car. Several have and, as a result, there are a few new parts installed that they could have done without (fuel pump, main relay and some other things). Also, there are components dangling everywhere as people ripped things apart. But, at least they didn’t start cutting up the wiring harness so everything should go back together. Since these guys couldn’t find anything wrong, they would all conclude (without further testing) that it must be the brain. Well, even a stopped clock is right twice a day (if on AM/PM of course). I like your tag-“don’t guess-troubleshoot”. It’s what I do and works in most cases.

I’m curious about what seems to be a gap in information about the ECU numbering system. The last three digits are briefly referred to as version numbers but, unlike the middle three-deemed the most important-no charts or lists are offered. Now, one would think that version numbers might differ only slightly and are less important. When I input ours on Ebay, it came up as civic 1998 auto trans. When our friend offered an ECU with correct middle digits but differing version numbers, I tried to get info on version numbers. Giving up, I searched for his on Ebay and it came up 1998 civic with manual transmission. To me, that’s quite a difference for just a version number but it is true that auto vs. manual is a different version of car. However, that is significant so I don’t understand why information on the last three digits does not seem more readily available.

Thanks again,
jvf

 

https://www.hondata.com/tech-ecu-identification
https://honda-tech.com/honda-civic-d...1/#post9057564