ezone

Sounds like the PCM has gone stupid.
Tighten the alt bolts like the bulletin says and hope it works right again with no permanent damage.

Wirenut

Ok, maybe stupid question? Are we talking about the mounting bolts or the electrical lug bolts??

ezone

I meant the mounting bolts.

PCM "goes stupid" and gets damaged when exposed to high voltage (alternator housing ungrounded causes this), and if you left the nut loose on the big wire you would have a low voltage problem.

Wirenut

Thanks again ezone.. I'll check it out in the morning and post my findings. Fingers crossed!

Wirenut

Well alternator bolts tight.. Grounds were corroded, so cleaned them up. still same issue

ezone

I just realized you didn't actually say what all symptoms you had, only that you said "Same problem for my 2001 civic." I was guessing yours has no communication with a code scanner, gauges go crazy, relays clicking away, idiot lights, limp home mode running, etc. like the other posts have.

Does it?

Corroded grounds could cause high charging voltage.

Even though the info says the common cause is loose alternator bolts, it also stated the PCM damage is caused by high voltage (regardless of what caused the high voltage).

Read up all of that bulletin info I linked earlier. That bulletin described the common symptoms, and also says to check for powers and grounds at the PCM before you condemn it.

I just can't picture any other simple reason why this episode would happen after a compressor R&R, unless you did something I wouldn't have done.....like unbolting other grounds from the body or something.

HTH

MikeFortin

Hi there, No clue if anyone is still looking at this.

I'd just like to know if I'm on the right track here. I bought this 02 Civic for my GF 2 years ago. When we bought it, the gauge cluster were acting up a bit ( Couldn't see exact mileage of the vehicle until it warmed up for 10 minutes, and fuel gauge was innacurate). We weren't too concerned about it at the time and thought we would get to it. I remember when we bought the vehicle the alternator belt was squealing and when I brought it in to the garage, the guy was saying the bolt was so loose it was about to fall out. So he changed the belt and made sure to tighten that bolt properly.

Fast forward to 1 week ago, the car goes into limp mode and when trying to get info from obd reader , we get a communication error. So from what I'm gathering here, would it be fair to assume that the alternator bolt being so loose caused the ECM to fry back then, which would also explain the whole gauge cluster issue? I resetted the ECM by removing the fuse which cleared the check engine and basically the limp mode. Drove the car for 25 minutes today just fine but still had the same gauge cluster issue. However, I am well aware that this is a temporary fix and would like to get it fixed without bringing the car to the dealership and spending more than what its worth.

Note that I have ran the Self Test on the Gauge Cluster unit itself to ensure that the unit itself was functioning properly. So at this time I am really turning towards that ECM Being damaged during this whole alternator fiasco. What are you recommendations? Should I go ahead and change the ECM ?
Thanks,
Mike

ezone

Could be a brand new problem too. Have the alternator bolts come loose again? Is the alternator failing (super high voltage output)? Bad ground cable/connections from battery to frame and drivetrain?

Stop running the engine until you get this figured out. As long as the PCM can still communicate at times it might not be ruined. Yet.

If you connect another PCM without making sure the root cause is solved, you'll ruin it too.

Did you plug in your code reader to see if it lost communication during this event? That will probably be a big clue.

MikeFortin

Each time I've plugged in the obd reader to get the a reading, I'm getting a communication error code. I will try it again tomorrow. I'll double-check my grounds again, but my theory was that the damage to the PCM would of been done back when the alternator bolts went loose. Last week was the first time in two years of owning the vehicle that it went in limp mode.

The cluster never fully comes back either, once the vehicle is warmed up , the mileage comes back fine but the fuel gauge is still always unreliable.

ezone

Do not start the engine. Just turn the key on and see if it can communicate.

I think if the PCM was seriously damaged back then, it wouldn't have waited 2 years to start being a problem now.

That's why I think the root cause might be an all new problem. Or a repeat problem.
Just those 2 items are affected? That's probably a cluster issue, separate from any PCM related issue. Those 2 items aren't really on the data bus the rest of the gauges operate on.

Many times when the PCM loses communication with a scanner, the speedo/tach/temperature gauges might go whacky and warning lights go nuts, along with relays clicking under the dash, and other stuff depending on the severity of the problem.

MikeFortin

So.. we've had the issue where the cluster goes entirely nuts like you say, where we would lose all data and hear a bunch of clicking, but it was just occasionally.
Mainly it's the mileage that just shows a bunch of 8888888 for about 10-15 minutes and the fuel gauge is unreliable.

I have however ran the self test on the cluster itself and it passed every test on every single gauge. Hense why I was assuming that the issue is greater than the cluster itself.
Would you have a recommendation of tests to do in an order to isolate whether there is still a root issue or not before I go out and put a new PCM in there ?

ezone

That's when the PCM is "frying" and communication to the gauges is interrupted

That's not happening at the same time as the other gauges going wonky, correct?

Cluster may be ok other than the odometer. It's just an LCD display. If you took it apart I bet the odometer would work if you manipulate it a bit.
Fuel gauge could be a sending unit problem.

Firstly, are the alternator mounting bolts ALL tight? Find that out first.

Do not start the engine. Just turn the key on and see if the scanner can communicate.

Unplug the alternator 4 wire plug. (so the alternator cannot charge)
Start engine, see if everything appears to work correctly. (except for the odometer and fuel gauge)
Now reconnect the 4 wire plug on the alternator. Alternator will begin charging. If things suddenly go haywire now, shut it all down and figure out why the alternator is causing it. (alternator is insufficiently grounded for whatever reason)

Perform voltage drop testing to figure out where/why the alternator lost its ground.

MikeFortin

Alright I will do that tomorrow morning and get back with results.

The odometer and fuel gauge happens All the time. Each time we start the vehicle. After a while of driving with it, the odometer comes back.

The cluster going wonky happens on rare occasions and the times it has happened, it only went on for about 5 - 10 seconds. I would say this happened about 5 times in the last 2 years.

Also, if I don't see anything wrong with the alternator after running these tests, where should I head from there ?

ezone

I wasn't expecting something like that.
Roll the dice? If you don't find and fix the root cause, then a new PCM will eventually get ruined too.

If the root cause was fixed 2 years ago but this pcm finally shot craps, then a new pcm alone should fix it.

Except for the odometer and fuel gauge. Those still sound like independent issues.

MikeFortin

Alright thank you very much for your help, I'll be back with answers.

MikeFortin

Update to this:
I took the gauge cluster apart and realized there were some broken connections. After fixing those, the dashboard, including the odometer and the fuel gauge came back to normal. At that time , a check engine light came up to which I was able to retrieve this time. It pointed me towards the TDC sensor. Replaced the TDC sensor and the vehicle now runs perfectly.
It's just funny that The weird coincidence of the dashboard and the vehicle going into limp mode was pointing me towards a PCM issue, but turns out they were two separate issues, thanks for your help !

darkwraith_kaid

Any help to be had here still?
I JUST bought this 2001 EX Coupe. The battery terminals were corroded as hell, so I disconnected the battery, cleaned the terminals and connectors, applied terminal protector, rings, and reconnected the battery; went to start the car and drive away and the engine only cranked, wouldn't start and run. Grabbed my voltage tester, 12.4 volts, looks fine. This time I turn key, no crank even, just very rapid clicking from under the glove box. Turned it off, pulled the key, locked up, went and grabbed my neighbor to have a look at this bull**** with me, come back, try to show 'em the clicking, but now it isn't clicking at all. Next thing we find is that the battery now has less than 11 volts and the positive terminal is hot to the touch. The car has had work on it before, but it's completely stock, however, whoever did the work, when they put the battery back in they put the ground somewhere retarded under the airbox, so I moved it to the strut tower. I've yet to even reconnect the battery yet, it's late at night, and I'm ****ing pissed. We checked all of the fuses in the under-hood fuse box and they're all fine, but haven't tested the under-hood relays yet, however, I think they're fine. I've got the belly of the dashboard opened up and the glove box out to have a look at all that **** in the morning. Fan-****ing-tastic way to spend my Sunday, and this thing is my DD. ****.

Slumpertcivic

Colin42

Check if the positive wire is all corroded where it joins the battery terminal. I had a similar problem with my girlfriend's car, removed the terminal, cleaned the hell out of it and cut back the wire like an inch to get to clean metal. Also check all your grounds, I think theres 3

ezone

Um, you sure? Maybe your drivetrain has no ground now. There is this ground cable pictured and one attached to the transmission, both are kinda stuck under the air box