Acemcguyver

I’m at the point where I could use some guidance on where to go from here, I’m tracing a ground in the system that is blowing the #44 fuse, specifics are as follows:

Vehicle: 1997 Honda Civic DX with Automatic trans. 1.6 engine, ECU code is 37820-P2E-338

Problem: Main relay cooked with puff of smoke behind dash. Main relay was replaced. Now #44 15 amp fuse in engine compartment keeps blowing when key is turned on. Fuel pump does not run and engine cranks but does not start. In the main relay, the 1st relay clicks but the 2nd one does not.

Troubleshooting: Found out the hard way that the wiring diagram may be more of a holistic view and not really what is wired on the car. The fuel pump works and is not locked up. There is continuity between the main relay and the fuel pump.

There appears to be a dead ground in the system. I’ve isolated it down to the Yellow/Black wire that connects the main relay and the ECU. There is a connection plug on the Driver’s side Strut Tower, I’ll call it the DST plug for short. The Yellow/Black wire goes through it.

If I disconnect the DST plug, the fuse does not blow with the key on. If I remove the Yellow/Black wire from the DST plug and re-connect the plug, the fuse does not blow with key on.

With the key on, there is power on the side of the harness that goes into the firewall, I haven’t traced the wire but I think it goes to the main relay under the dash on the passenger side.

If I take a test light, hook it to power and probe the Yellow/Black wire going into the engine harness end, goes under the intake, the test light lights indicating a ground. Tracing that wire leads me to Pin 11 on the ECU A plug. Pin 24 on the ECU goes into the engine compartment and powers the injectors and IACV, both indicate ground with the A plug connected.

If I disconnect the A plug from the ECU, the Pin 24 wire is open with the injectors and IACV plug connected. So that tells me the injectors and IACV are not causing the ground.

So that leads me to the ECU, when I open it up it looks pristine, no smell of burnt electronics and everything looks good. With all the plugs disconnected from the ECU, when I ohm pins 11 and 24 on the 1K scale find they connect to the ground pins 10 and 23, slightly less than a direct connection but direct enough to indicate strong continuity and possibly blow a fuse.

So that generates some questions:

Is this a normal condition for pins 11 and 24 in the ECU? Does the ECU ground pins 11 and 24 and then switch away from ground when the key is turned?

Is the only way to check the ECU to swap it out with a good one? What other ECU’s can be used in place of a 37820-P2E-338?

Is there anything else to check, like a wire off of plug A that could be going to ground? I thought by unplugging the ECU and finding a ground that I eliminated most any harness or sensor issues.

Any help finding this thing would be appreciated

Former User

If you unplug the IACV and all 4 injector clips, does 15A fuse 44 still blow?

Acemcguyver

Yes it does, everytime.

Former User

Carefully inspect the Yel/Blk wires at junction connectors C116 and C130.

If you unplug C130 (remove end cap), does fuse 44 still blow?

Do same unplug test for C116 if removal of the C130 end cap prevents fuse 44 from blowing.

(C101 is the connector you unplugged that prevented fuse 44 from blowing.)

Former User

The picture below shows an example of an end cap removed from a Honda junction connector.

Acemcguyver

Yes, I know plug C116. I will check for the specific condition(s) tonight but I do know that when I unplug the jumper cap from C116, I believe it's pin 1 on the plug which goes to ECU Pin 24 goes to ground through the ECU. When I unplug the A plug from the ECU, pin 1 at plug C116 is open. None of the other Yellow/Black wires, (Inj and IACV) go to ground with the jumper plug off. I haven't seen C130 unless it's the green plug attached to the side of the ECU but probabaly not as your diagram says it's brown.

Former User

Does this^ prevent fuse 44 from blowing?

As you can see in the C116 connector diagram, pin 1 of C116 is unused. Double check the pin number.

If you look at the diagrams I posted, the circuit is actually organized like this:

C116 <-- C130 --> ECU connector A (A11, A16, A24)
................^
.............C101
................^
..........main relay

When you unplug ECU connector A, you disconnect the circuit from all three of these ECU pins (A11, A16, A24).

I think A11 and A24 should be grounded constantly as they receive main relay voltage to power the ECU. But you can easily test whether the ground you detect is causing the short by unplugging ECU connector A to determine whether fuse 44 no longer blows. If the fuse does not blow, then the ECU is bad. If it blows, do the C130 and C116 unplug tests that I mentioned. This will help you pinpoint the short.

...as expected based on your other tests.

C130 is brown.

Acemcguyver

So, I put everything back together and pop off the jumper cap on C116, the fuse does not blow. I found C130 and with the cap on C116 and the cap off C130, the fuse does not blow. So with either cap off, the fuse doesn't blow but with both caps on, it blows. With the ECU A plug pulled, the fuse does not blow.

What I though was pin 1 at C116 in my earlier post going back to the ECU through C130 is pin 3, I noticed pin 2, (IACV), showed a little ground, so I disconnected the IACV and capped C116 and it still blew the fuse with the IACV disconnected.

So I'm thinking, the only connection between C130 and C116 that I can see is the wire going to pin 3 in C116. The fact that the fuse doesn't blow when the C130 cap is off tells me the ground is upstream in the harness, at C130, that's why I can pull the cap on C130 and the fuse doesn't blow. So if my logic is correct, one of the Yellow/Black wires on C130 is grounded. I would think the next step would be to disconnect ECU plug A and probe the yellow black wires at C130 to see which one goes to ground. Is my logic sound? Do you have a diagram of where the C130 plug wires go?

Former User

The fuse doesn't blow with the C130 cap on and the C116 cap off, so the short is downstream of C116. (where battery is upstream and ground is downstream)

If this^ is true with both the C116 and C130 caps on, then the short is somewhere between C116 and the fuel injector/IACV clips. I recommend that you start by looking for shorted power and ground wire terminals in each fuel injector clip and the IACV clip.

Acemcguyver

So, it looks like I have a dead short (ground) in the system but another way to look at this is that I could have a high load condition. They often look the same but are technically different. The only thing in the engine harness at C101 that had any kind of a load was the IACV, so either the load on the IACV was to high or it was enough to put the 15 amp circuit over the 15 amp mark. It seemed to me the ECU had a higher load condition between the power and ground pins so I took a trip to the junk yard and finally found an ECU out of a 98 Civic. Plugged it in and it didn't blow the fuse with everything connected and the key on, so I rolled it over and it fired right up. I don't know what happened with the ECU, they are usually not the problem and it certainly didn't look like it was but it was obviously the issue with this one. Many thanks to RonJ@HT for the diagrams and the assistance with narrowing this one down, your information was most helpful and I appreciate it.

I have one further question for anyone who might know. The original ECU is a 37820-PE2-338, I relaced it with a 37820-PE2-L82, obviously it works right now but is this an adequate replacement or will it give problems later on?

Acemcguyver

So after running for a week, I get a check engine light and a P0453 and P0450 code, EVAP fuel tank sensor high input. I found this thread
http://www.ff-squad.com/technet/code91.htm
but I don't know if this my issue. Does the 97 Civic DX even have the sensor the computer is checking? Apparently, the 98 Civic DX does have the system. So, if the 97 does have it, it's normal troubleshooting to find the problem, but if it doesn't, then I guess I need to look at getting the right ECU for the car or fool it. Any thoughts?