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I have never seen anything like this - has anyone else ?
So, my wife was driving our 2004 Honda Civic LX Sedan with automatic transmission home this evening. The check engine light came on and then the following happened. The RPM and Temp gauge both fell to zero and stopped working. It's like the transmission is stuck in high gear. You can only get the car up to about 50 miles per hour before it acts like either the tranny is slipping or it's not getting enough gas or something. And, at AutoZone they couldn't get the OBD reader to work to read the codes...

I am going to pull the negative battery cable tomorrow and check all the fuses and hopefully if things don't start working maybe they might be able to start reading the OBD to get the codes.
Anyone have a clue to what this might be?

 
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Alternator is loose?

 
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charge battery or change to a new one and test.
if it works, either the battery or alternator.
lack of electrical power makes electronics do weird stuff.

 
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get the code read.

 
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Get that code read. Hopefully not related to your transmission replacement you recently had done.

 
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Thanks for the input on this...

The code reader couldn't read the codes, which was one of the many things that just started happening all at once. But, the alternator was loose due to the adjuster bolt snapping off. I got the alternator off now and will be attempting to get what's left of the bolt stuck in the alternator off. If this is all it is I'll be happy. Taking the alternator off of mine was a pain because the bolt is way too long. If the bolt is still in good shape I'm hope to simply cut off what not needed. See what happens. I'll update this after getting the alternator on - hopefully that's all it needs...

 
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Other times when we've seen the alternator loose and the PCM not communicating with code readers it turns out to be fried and in need of replacement. Hopefully yours begins working again.

 
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Sounds like when someone forgets to tighten all of the alternator bolts, now the PCM may be ruined as a result

 
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I certainly hope the pcm isn't fried. We bought the car used. Not sure if the alternator has been loose since the beginning or what. I haven't worked on the alternator. I wouldn't think the person that did the transmission rebuild would have a reason to. We also had the same guy replace the two front cv axles. Either way - I sure hope the pcm isn't fried.

I got the bolt that broke out off the adjuster part of the alternator and I cut the bolt main top bolt down a bit so I can get the alternator back on easier. Still have to go get a new bolt.

So, sometimes the PCM fries and sometimes it doesn't due to a loose alternator - man, that just doesn't sound right, sure sounds like a design flaw. Well, I'll know by tomorrow afternoon sometime, weather permitting.

I've always been told Honda's are nice cars, but this is the first lemon I've ever own at 55 years old.

 
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sadly, the alternator loose causing it to fry the PCM is a known common issue in these cars.

failing auto-trans are common in the 2001, 2002. Blown headgaskets are also common - look into the overheating sticky thread. every 100k miles.

If it does not come back, look for used here:

https://www.civicforums.com/forums/1...-part-com.html

Notes:
1) get from auto car, manuals might cause problems (some sensors in the auto trans vs manual)
2) Do not get an EX car PCM - they will have VTEC, yours LX does not - it will give a code that it cannot find the VTEC and keep it in limp mode
3) Starting from the 7th gen, (2001-2005) there is an anti-theft function - key have a chip that the PCM will read - if not programmed, it will not start. Looks like regular keysmiths nowadays can program them too, otherwise you will need to take to a dealer if you can't find one to do it. Or you can see if you can get the PCM, keys and drums from the same car in the junkyard (mostly the ignition that detects the chip, but iff you want only one key, need doors, ignition, trunk and the rear seat lock). PCM should be around 100 bucks, not sure about the keys/drums. They will need to come from same car

Edit:
4) 04-05 have the wideband O2 sensor, so recommend getting PCM from 04-05. Not sure if you would have issues with the wideband sensor coupled with narrow band PCM. Having a narrow band sensor coupled with a wideband PCM for sure will not work.

 
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If the alternator is installed properly it's not a problem

 
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I get what you are saying, but at the same time while searching the web about this I am finding a lot of references to the alternator bolts coming loose and also breaking. I've been reading that it has something to do with a grounding issue when they come loose. If a grounding issue is the case, well, that is just plain a bad design in my book. Either way, I'm hoping and praying my PCM isn't fried.

 
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Realistically here, this really only happens after someone with wrenches touched it.
No. The design assumed someone with wrenches getting all of the bolts tightened correctly.


You'd probably argue the same if some mechanic forgot to tighten one of your wheels.......right?
Look for and fix these typical issues first (don't forget all of the battery/chassis/powertrain grounds), then see how it goes. If the engine computer comes back to health and 'talks' to a scanner again, you win.




If you replace a computer without fixing the root cause, you will ruin another expensive computer.

 
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Thanks for the info/input...

"You'd probably argue the same if some mechanic forgot to tighten one of your wheels.......right?"
No, a pcm frying because of a loose alternator bolt is a bit different. To me, that's just not an acceptable design. That's like hey a bolt came loose on the kitchen sink so your electricity shorts out and your house burns down type thing - lol. I guess we'll have to agree to disagree like ford and chevy guys use to when I was younger or may still do I guess

"don't forget all of the battery/chassis/powertrain grounds"
I did that a while back but can't hurt to take a second look at them though.

I got a power steering belt (the alternator belt looked in great shape) and a new bolt to replace the tension/alternator bolt that snapped off. The broken part left in the alternator came out using my fingers with the help of a little PB Blaster. So, come tomorrow afternoon sometime I should know one way or the other. If it is the pcm I'll probably try the used pcm with keys and ignition thing or swap out the key chips or something. Wow, man, I sure I hope I don't have to go that route. Life goes on...

 
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good luck and keep us posted

 
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Well, the alternator and power steering are back in, grounds are good as far as I can tell, and the alternator seems to be working fine. Had 12.55 volts on the battery and the alternator would kick it up well into the 13 volt range when you gave it it a bit of gas. The RPM gauge is working again, not sure about the temperature gauge as I didn't let it run long enough to check as there are still issues. So, here's what going on now...

With the car sitting and idling the rpm's are spiking up a bit and the dropping like it wants to stall. The engine light is flashing on and off in harmony the varying rpm's along with a clicking from behind the glove box, which means the pcm is probably the cause of the clicking. There seems to be an intermittent battery light, not sure why as the car limped about 20 miles home with the headlights on and a loose alternator and belt and still has 12.55 volts left in it, so that battery can't be too bad.

That's where I stopped, put the tools up and figured I'd post and update here and see what you guys thought about it at this point.

 
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recharge battery with a external charger, try again

 
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Thanks for the tip. Got it on the trickle charger now. I removed both battery cables from the battery to completely isolate it from the cars system. Once it charges completely I'll hook things back up, give it another try, and post the results.

 
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But the loose alternator would have been supplying insufficient voltage and amperage to charge the battery.

Take her for a 30 minute test drive, bring your tools, stay close to home, and make sure someone is close by to come pick you up.

 
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Still trickle charging - I guess it'll be tomorrow. Once it's charged I'll take it for that drive and see what happens.

 
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Well, bummer.
With a fully charged battery here's what I have.
Start the car and let it idle,
the rpm's go to about 1.5,
the engine light flashes and the PCM clicks,
the rpm's drop down to about .5 to .75 rpm's,
this cycle keeps repeating for maybe a minute and the whole time this is happening the battery light is on steadily.
Then there will be one final click, the rpm gauge drops to zero, the battery light goes out, and the engine light comes on and stays on.

So ???
Any thoughts on what to do from here?
I didn't go for a drive as suggested because the battery is fully charged and the car is still acting up, so not sure if I still should or not type thing.
Thanks...

 
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So, I limped the Honda over to Advance Auto Parts and their code reader just showed a can not communicate/link type error. It's still acting like it's stuck in high hear whether it's in 2nd, 3rd, or drive (it doesn't shift up or down at all). I assume it's time to buy another PCM, unless someone knows something else I can try ???

Thanks...

 
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Looks like you're buying a pcm, make sure it's for the same engine and trans that you have. 01-03 are different than 04-05.
You're 100% sure that the alternator is correctly installed right?
You don't want to do all this work and then have to repeat it.
Call local locksmiths and see if they're able to program it otherwise you're taking it to Honda.

 
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next is either PCM/Keys or Alternator... (alternator failing is actually another weak point on these cars...) if alternator is bad, PCM will soon follow... ask them to check before replacing

 
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Yepper it's installed properly - even added a little goop on the threads to help insure they don't come loose. I've been working on my own cars for many years, but this is a first timer for me. I'm not afraid to ask questions, etc

 
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I've got the PCM removed and the it has the following numbers on it:
37820-PLM-A72 6W
28?7-147979
It's my understanding that the first line 37820-PLM-A72 is the important information to match when replacing the PCM.

I'm pretty sure the alternator is working fine as we had no issues PCM/alternator/battery wise that was noticible before the bolt snapped on the adjuster. But, being as it can't hurt and you suggested it worth's checking I think I'll get it checked before putting the new/used pcm in. Two different places just got an error when trying to read the codes, so I'm pretty sure the PCM is fried based on everything I've been told here and found elsewhere.

 
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I don't remember reading this critical information in your original post

 
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Post #6 above.

I've found a PCM with key and immobilizer and purchased it, just gotta wait for it to come in now.

 
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Got the PCM back installed. However, the ignition setup with the new key is just hanging for the moment. I've got to figure out how to get the two bolts or what ever they are holding original one onto the steering column off to put the new one on. It almost looks like they put two screw in and the ground the heads round. Not sure if the are pressed pins or bolts. Not sure if I need to grind them off or what. Has anyone here done it before?

It starts, runs fine, took it for a test drive. But, for some reason the clicker to lock/unlock the door isn't working. Not sure why.

The only tip I have so far replacing the PCM on a 2004 Honda Civic LX four door Sedan is to remove the air/heat actuator and the brace the PCM bolts to in the front - the PCM will slide right in/out. NOW, WARNING, getting the screws out of the air/heat actuator is a pain and you'll need a stubby Philips screw driver and/or one of the thumb wheel type ratchets. For me, it was either yank, pull, heave ho on the PCM or struggle with the air/heat actuator. I imaging there is an easier way, but this is my first time on this vehicle, and well, I got'er done - kind of - still gotta do the key/ignition thing.

 
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the heads snap off when you install the bolts, security feature,
use a chisel and a hammer to unscrew them or grind a slot in them with a dremel.