Location of the CKT 25 circuit

After doing everything I can under the hood , to find an intermittent charging problem , with the battery warning light, I've come to the conclusion it is elsewhere. My car shows three codes with history written underneath them, codes E039, B410 and C553. I don't know what the C533 means, I could not find it. E039 says something about a torque converter circuit, but the B410 says there could be a problem between the BCM computer and circuit ckt25 . Does anyone know where that circuit is located, is it under the dash. or the hood, I can't locate it in the manual. I believe the BCM in located under the glove compartment according to the manual. I'm thinking maybe there is a bad connection in one of the connectors or a bad BCM, I still have to do all the tests. One of the things that has bugged me about this car, on a cold engine, open mode, it will idle fine until it goes into closed loop, then it has an erratic idle. I always thought it should be smoother that that, maybe it is a bad BCM. Thanks.

A couple of things. First, what year, 88 or 89? The electrical systems vary somewhat by year so we need to know this to troubleshoot correctly.

Second,the C553 code is a CRTC code indicating loss of power to the CRTC module. Could be caused by a battery disconnect or any other loss of power (such as charging system malfunction).

Third, the BCM is located directly behind the glove box and the glovebox must be removed to access it. The ECM is located further down in the passenger side of the dash (beneath and perpendicular to the BCM against the outside wall of the footwell). As a side note the BCM has no effect on the engine, that would be under the purview of the ECM.

Finally, looking at the 1989 FSM it appears there is a misprint in which circuit (CKT) 225 is repeatedly referenced as CKT 25 on pages 8D2-42 and in the troubleshooting tree on 8D2-43. Circuit 225 is a red wire that runs between BCM terminal 3D15 and the "L" terminal on the alternator (shown as generator in FSM). The misprint is undoubtedly causing you unneeded confusion. I did not check the 1988 FSM to see if the same mis-print was extant there as well.

KDirk

I'm sorry, it's an 89 . I am starting to see why I'm getting a C553 code, because of a battery disconnect , so that explains that one. I'll start checking out that red wire back to the BCM. Thanks for that info.

Mike

KDirk, I check the plug in on top of the alternator, the red wire goes to L and the light green wire goes to F, so far so good. My question is, under 8d2-42 , the alternator diagram shows a ground wire coming off from the alternator to the battery, I don't have this wire. Am I right in assuming the alternator is grounded through the bolts and frame , or not.

Mike

Mike, I had to look at my 88 (don't own an 89) to be sure, but it appears the alternator relies entirely on a frame ground. Only wired connections I see are the heavy battery cable bolted to the rear terminal and the two wire harness on top.

If you have an ohm meter measure from the alternator case to the negatve battery clamp (with battery disconnected preferably) and see if uyo are getting high resistance. Anything over a couple of ohms could indicate a marginal ground somewhere. You could also use a continuity tester, if it beeps doing the above check, then you should have a good ground.

KDirk

With an ohm meter I checked out the continuity from the case to the ground post under the coil pack, it looked okay. Although after your reply, I think I will recheck it again from the case to the ground cable on the battery, I'll have to disconnect the ground battery cable. If that checks out I guess my next step will be to do the diagnostic testing. At some point, if I have to access the BCM, I think I will check out the connections on the ECM. After 25 years, some of those connections might be a little tarnished. I appreciate your help. Thanks,

Mike

Two questions. When looking at the diagnostic diagram, 8D2-43, the computer shows a low reading to step 2, with the alternator connector unplugged. Should I re-plug the connector before going to step 3? Step 3 talks about unplugging the #3 connector from the BCM before continuing, I have not accessed the BCM yet. I looked at a photo of a BCM with Rockauto, it appears there are three connectors on the BCM. does anyone know which one is #3.

Mike

Okay, I answered one of my questions after looking further. There are three connectors on the BCM, two have the color black and one red, #3 is the red one. I'm still confused about reconnecting the alternator plug in. Thanks.

Will need to look at the book myself to answer that, will be late tonight as I am away from my "manual library" presently.

KDirk

No need to reconnect it, but it ultimately won't matter either way. You're looking for the reason that the BCM reading is staying low when it should be high. Removing the alternator connector sees if the alternator is that reason. Since it stays low, that means either the red wire is shorted to ground somewhere along its run, or the BCM is defective. Disconnecting the #3 connector from the BCM removes the red and green black wires and the alternator (if still plugged in) from the equation. If is still says low, then the BCM is defective.

I hate to say it, but I read the screen wrong. I was looking at the little arrow on the bottom which had low under it. So now the way it stands, instead of low low with the key off then engine running, it now reads low to high. Tomorrow I'll have to check out the value of bd51. It says that if the value is below 7% , I have to take a test light from voltage to pin f in the cavity of the alternator. I assume I have to connect one end of test light to the ground post on the battery, then the other end to pin f, does that sound right? Then I have to recheck the valve of bd51. I'm a little worried about shorting something out, of course it might be above 7% . Thanks.

I have to take a test light from voltage to pin f in the cavity of the alternator. I assume I have to connect one end of test light to the ground post on the battery, then the other end to pin f, does that sound right? Thanks.

No. You do not connect any end of the test light to ground.

One end is clipped to the positive side of the battery (can be right there at the B+ terminal on the rear of the alternator) and the pointy end is stuck into terminal F in the connector you removed from the alternator. That's what test light to voltage means. You are looking to see if the BCM sees the voltage you are connecting via the test light and reports a value over 80 for BD51.

Because you are supplying the voltage thru a test light, you don't have to worry that much about probing the connector. Not nearly as hazardous as just connect it directly to the battery.

Keep us posted.

Thanks for getting me straighten out on that test light voltage, I learn something everyday. I checked the value of BD51 and it does not give out a percentage, it just shows the numbers 33 and 34 flashing back and forth. I was also wondering about the connector J8 at the firewall. Is that the one on the far upper left corner on the passenger side. If so, it looks like I'll have to remove some plastic to get to it.

Mike

Thanks for getting me straighten out on that test light voltage, I learn something everyday. I checked the value of BD51 and it does not give out a percentage, it just shows the numbers 33 and 34 flashing back and forth. I was also wondering about the connector J8 at the firewall. Is that the one on the far upper left corner on the passenger side. If so, it looks like I'll have to remove some plastic to get to it.

Mike

Negative. J8 is in connector C216 which is a 56 cavity connector inside behind the right side of the dash near the ECM. Probably just as easy as to get to it at pin D11 on that #3 connector on the BCM.

Was that 33 reading when you were looking for more then 7, or when you were probing looking for a reading of 80+ ?

It was when I was looking for the 7, I have not yet used the test light. If 33 means percentage, (don't know), which is higher than 7 , then I guess I have to move over to the next step. Is that the way you see it.

Mike

It was when I was looking for the 7, I have not yet used the test light. If 33 means percentage, (don't know), which is higher than 7 , then I guess I have to move over to the next step. Is that the way you see it.

Mike

Yes, time for the next step to see if code comes back.

33 is a percentage value of the target output voltage the BCM is trying to get the alternator to put out. I'm thinking it's about 14 volts or so.

Thank you, have a nice weekend everyone.

Mike

I checked lines 23 and 25 from D11 and D15 to the alternator plug with an ohm meter, could not find any resistance. So I hooked the battery back up and put everything back together,codes were cleared, then took the car for a test ride. I took the car down a bumpy road where I live, about thirty miles an hour, no problem so far, no battery light. Then I got up to speed to get on the freeway, that's when the battery light came on. I just changed the fan belt two days ago, so I don't think that was the problem. When I got back to the house there was no battery light and voltage was okay. Looking back at some of the things I did to this car, I changed the size of the hot lead wire from the alternator to the battery to 4 gauge. I think the original size was 6 gauge, correct me if I'm wrong. I'm wondering if this was the wrong thing to do , they told me at the parts store it's okay to increase the size. I came across a chart that says if you are within 4 feet to go with 14 gauge. The other thing I did was increase the size of the smallest ground that comes off the battery to 6 gauge, I think it goes to the body frame,there are three ground wires. They are now 6, 6, and 4 gauge. Did I mess up increasing the size. It seems like the problem starts when I rev up the engine. Thanks.

I can't imagine changing the wire gauge on the primary cables had any bearing unless you have a poor connection on one or more of the new cables. Have you checked for belt slippage at the alternator pulley? For that matter, are you certain the alternator is 100% good? Sounds as though it could be intermittent belt slippage or poor output from the alternator at issue here. The fact it happens at highway speed makes me lean towards the belt slipping (or the alternator pulley not rotating freely at higher engine speeds, which would have the same effect).

KDirk

I agree with KDirk, sounds like belt slippage to me. Maybe a new belt tensioner assembly is needed.

I tend to agree with you. I did find a chart under electrical diagnosis in the data base , that shows that wire to be a number 13, which I assume is 13 gauge. On the other hand last Sunday I took the car for a spin to a park, after we had a little picnic, I started the car, then I got all the warnings. So if it went that far I don't see how it could be the wire, don't know. Maybe it's this Texas hot heat affecting a bearing. When I changed out the belt, the pulleys seemed okay, but that was on a cold engine. The alternator was rebuilt by an alternator shop. Although when I had it checked out by them they told me it was okay, but they said they wanted to keep it for further testing , only to find out it had a bad regulator to the tune of $185.00, I wonder. I think I'll start looking for a bad bearing on a hot engine.

Thanks.

I too agree with Kdirk (he and a few others are very good at trouble shooting on these vehicles & much of their knowledge can be applied on most any car). Changing the wires should not cause the issues you are having. I would look toward one of the pulleys dragging the belt to slow it down and cause your issues. You can do a quick check by spraying some belt dressing on the belt to see if your problem goes away. It will help you identify that a pulley is causing some slippage and you really need to fix the mechanical problem sooner that later.

I was thinking the spring in the tensioner more likely than the bearing, but anything is possible.

I just saw a video on a bad tensioner and how it reacts, I'll check it out tomorrow, it could be the culprit. I changed out the pulley a while back but not the tensioner. It could be the original one on this car, this car has 122,000 on it, so it is time to replace it. I read where you should replace the tensioner anytime you change the belt, might be a good idea. Thanks.

Mike

I was thinking the spring in the tensioner more likely than the bearing, but anything is possible.

That's a good idea. Seldom ever think about the tensioner. Damn good idea.

John F.

I'll bet a different alternator will cure your problem.

I'll add that I have very little confidence in rebuilt alternators. I have had many bad experiences (defective out of the box, premature failure after a few weeks or months, etc.) with reman alternators. Last two I replaced I bought brand new aftermarket units with upgraded output ampacity. Both have performed flawlessly since installation.

Point being, do not assume it is right just because it was rebuilt and tested. Don't even make that assumption on a new part for that matter.

KDirk

The dang voltage regulator causes a lot of problems. My girlfriend's car has that issue, and it will put out 14v when it runs, so "Tex" at the alternator shop said it was ok. Standard tests don't always catch a flaky voltage regulator.

There may be some truth to this.

I've had an issue with flickering headlights for some time now.

I've pulled the alternator and had it tested at three different places. AA, AZ, and an independent shop. They all say that the alternator checks out good.

What else could it be?

John F.

i agree with Ronnie and Kevin regarding a bad alternator.

long story short, i replaced my alt with a rebuilt from Advance. about 2 or 3 weeks later with the rebuilt, i started having problems with it going into the 11's, then back to the high 13's or low 14's. i verified the CRT voltmeter readings with a separate voltmeter. i took the alt out and took it back to Advance. the first run thru the "machine" showed no problem. i told the "kid" to run in thru again and it started acting up. the alt was replaced at no charge and never had another problem.

John, re the headlight flicker - i'd have to start with a corroded connection/wire/ground or a crimped wire. never had that problem on my Reatta, but did on my '80 Corvette. turned out to be a corroded ground wire connection.

Well, I think I found my problem, it ended up being the alternator pulley, it had a wobble to it. I don't know why I didn't see it before, I guess I got to get a better drop light. Anyway , I installed a new belt, tensioner and alternator. Took it for a test drive , so far so good.

Thanks guys, I could not have solved the problem without you.

Mike