Civic ECM failing?

Our 98 Honda Civic with 235,000 miles is acting oddly. At highly irregular intervals, usually at high speed (but not always), the check engine light will come on and the engine will quit. Sometimes for as little as a second (in which case the car continues on it’s way) or for as long as a minute. The light goes off and leaves NO CODE for reading. Igniter and coil have been replaced. Other sites indicate similar behavior in failing ECMs. No other electrical trouble. Runs great otherwise. Got an opinion?

No, the ECM (engine computer) is fine. Honda engine computers very rarely go out.
The PGM-FI Relay (“Main Relay”) is your problem. These relays have a history, after about 8 years, of faulting. They cause no-starts, and stalls. This relay controls power to the fuel pump, fuel injectors, and the engine computer. The distributor was the first suspect.
The ignition switch is another suspect. If you momentarily lose power to the things the ignition switch normally powers, it will cut the engine off.
I have, and have had Hondas. I have experienced a failed PGM-FI relay.

If no codes are being stored it’s going to be very difficult to figure this out.

I’m not an expert, but if the CEL comes on and no codes are stored I’d suspect the ECM. Normally, if the CEL comes on a code is stored. At least that’s how it’s supposed to work.

I’d want to check all major electrical connections, including grounds, before replacing the ECM. A bad connection in the ignition circuit or the ECM circuit might explain this. Or not. Again, I’m not an expert.

Does your mechanic have an opinion about this?

Do you know anyone who owns a similar car? If you could swap ECMs with another car you might learn a lot. The cars would have to be the same. Same engine, same transmission, etc.

I’m sure a new ECM is very expensive, and you don’t want to buy one if it’s not necessary. Have you considered trying a used ECM from a junkyard?

Sorry I can’t be more helpful.

My mechanic offered the same thought about a failing relay. He said it’s located under the dash and typically fails as it gets hot sitting in the sun. Open the door to cool things off and (shortly) off you go. It seems like an odd part to fail while under way, as this car is behaving. Have you experienced that?

We haven’t pulled the ignition switch, but that was an early suspect. Keys have been jiggled, switched, pressed this way and that to try to invoke a short. The switch has not be swapped out, but it’s never been abused, either. He decided (short of a removal and swap) that a failed switch was unlikely.

When the motor quits is the “Check engine” light the only indicator that comes on?, or do all the dash indicators light up?

Under my control, only the CEL comes on when the engine cuts out (sometimes for less than a second). It has happened to my daughter more frequently, and I’m not sure of her experience except to say that the CEL always is displayed. The CEL came on when I was driving it and stayed on, though the engine continued to work normally. It stayed on until I got to the garage and it still did not register a code, which is what’s leaning us toward an ECM failure consideration.

If I had to give a simple answer to your question, it would be that only the CEL comes on.

If it was a fault with the ignition switch, then other dash lights would come on as well when the engine quit.

Ah; good point. It’s sounding more like the main relay is worth at least a try. Would a failing relay NOT register a code? That lack of a code is the most puzzling part of this. I haven’t found a note yet that a symptom of a failing ECM is a lack of reading/holding codes.

I second hellokit. Sounds like a classic pgm-fi relay case. If you or someone you know can solder this relay can be repaired. Pry it open and redo the solder joints. It’s usually visible which one is bad.

Normally I’d jump at resoldering the relay, but for the cost of a new one, I’m reluctant. The Honda part is about $50 US, copies less than that. In light of the sensitivity of this part (apparently…) I’m inclined to just replace it.

The ground appears to be solid beneath a petrified bolt. Does anyone have another angle to this that hasn’t been expressed?

My question about a failing relay triggering a CEL but not leaving a code record in the ECM hasn’t been addressed. Any thoughts on that?

The PCM-FI relay is actually two relays in compound action. That sounds a little complicated…and, it is. The two-relays-in-one-case are interdependent. They affect each other.
The PGM-FI relay is turned ON by the ignition switch, and, it powers the engine computer. If the PGM-FI relay faults, and cuts power to the engine computer, HOW would the engine computer know that its power had not been cut by the ignition switch, as it normally is?

IF you want to resolder the PGM-FI Relay, here is how you would do it:

It took me ~10 minutes to open the relay and fix it when my 88 Accord acted up. It also saved me a trip to get a new one.

Much obliged for pointing out the ECM characteristics in the non-energized state (during a relay caused power out). That sounds reasonable.

I think the next step is to either resolder the relay or just replace it.

Thanks very much to all of you for your help.


Here’s the update: I pulled the main relay, found a very clear hairline crack around one of the solder beds, desoldered and resoldered it. I’m not a pro at that, but it looked exactly like the cone shaped joints in the help sites, although one corner of it has some speckles of debris showing on the surface. Overall, it appears to be a good, full fill of solder.

The car test drove for about 20 minutes at a full variety of speeds perfectly. Nice feeling. Then tonight, my wife and I took it to the movies and after maybe 10 minutes at highway speed the CEL came on and stayed on. The engine never went out (typical behavior prior to this fix) even for a second. The CEL survives shutting down, for a short stop or a long one (2 hours). One time prior to this fix it did this same thing (engine runs fine but CEL stays displayed), and that yielded no codes.

I did not resolder all the joints, only the one that had obviously failed. Go back and do them all?

No stall, runs great, can’t read a code this weekend. CEL is on. Suggestions? Refer to posted photos of relay. Hopefully I can get them both at once. Let’s see.

John in Flint

It could still be the ignition switch. It’s entirely possible the dashboard indicators will not illuminate if the switch fails.

Switch failures are common (even on non-Recalled cars) and considering that it’s free of charge you should get this done.

I’ll run down the ignition recall option. I’m guessing that’s been checked, as this was dealer serviced before I got it.

Are main relays so sensitive that a bench solder fix to a joint could invoke a CEL even if it’s otherwise operating correctly? That’s the current condition: I fixed the cracked solder joint (photos above in this thread), operationally fine afterward but the CEL came on during the second test run and has stayed on (approx 20 minutes of use spread out over 2-3 starts) ever since.

The thing about the switch is that any test, if done, may not even be valid.
One could test that switch 12 times a day every day of the month and still be bad even if shown good every time.

Plastic and heat caused by a high current draw do not mix well. The same current that causes the main relays to heat up also passes through that ignition switch and does the same thing to it.

I’d get the switch replaced under a Recall if it has not been done already. More than likely it has not and since it’s free of charge take advantage of it.

Somewhere in the back of my head I think I asked him to check on all the bulletins and recalls for this vehicle, and he said he and that all work in them had been done. But if that were the case, it doesn’t seem like he’d have suggested all the fiddling with the switch to try to make it fail. I’ll take it in tomorrow and we’ll see about the recall (thanks for the URL) and hopefully get a code from the CEL. The car is old enough that even a replacement switch could have gone through a full life cycle and be ready for replacement. I wonder if Honda would do that twice? Stay tuned.

This reply is out of the right order, but I wanted to say thanks for your good advice (dead on) and encouragement to fix the bad joint. All is well in that regard. The CEL code that came on afterward was for the cat. We turned that off and it’s stayed off. It might be legit, but that’s another ball of wax. I still haven’t got the service record, but that’s coming. So far, so good. Now onto the right door window regulator.

This one’s done: the car’s running like a top. Thanks to all for looking in and helping.

Now onto the next fix: the window regulator motor. There’s another chat on that one.

John in Flint