Intermittent transmission slips

Good morning.

First, are there any codes? Current or history?

16.1 tells me you have a bad alternator. The regulator is no good. The voltage should be 14 to 14.5 volts only. Anything beyond that is no good for any of the modules.

As far as the wire, it does look like a ground but since you have no other issues, it may be nothing. you could run it to the body and see what happens but I doubt it will make any difference.

Roy

https://www.2carpros.com/articles/how-to-check-a-car-alternator

Roy,

Since this is a new alternator, is it possible that the ECM is telling the alternator to put out that much power?

Also, the wrapping around the wire and the length suggests that it goes into a wire bundle of some sort. Any idea which one?

The regulator is inside the alternator itself. The ECM just turns it on and off.

That is a bad alternator.

Is there any harness around there at all? I cannot see from the picture.

Roy

Attached a screen shot of my code scan.

None of them are related to the transmission.

I cannot see the Body Control codes, too small.

Can you post the Body Control codes?

Roy

B2625, P0455, C0899. I do not think there is anything wrong with the transmission. Since the problem stopped when I replaced the transmission 2,500 or so miles ago, the problem must be electrical or with a computer.

Okay, if the transmission is slipping then there is an issue.

The C2625 does not show as a valid code. Can you verify?

Roy

C0899

C0899
Descriptor
Probable Causes
Electronic Brake Control Module (EBCM)
Rear Differential Clutch Control Module (CCM)

p0455

P0455
Descriptor
Probable Causes
Fuel Filler Cap
Fuel Tank Pressure (FTP) Sensor

It is B2645. Does not this collection of codes - especially given the high voltage output, suggest an electrical issue?

No, it suggests you have issues with these systems.

B2645 is a possible BCM failure. That may be related to the issue you have since it controls all body functions.

Roy

B2645

B2645
Descriptor
Probable Causes
Ambient Light Sensor
Body Control Module (BCM)

Can that light be caused by a faulty alternator or a bad ECM? I am asking because I was getting BCM codes before replacing the alternator. I did not get them after replacing it for almost 3,000 miles. Now they are back.

The only way the alternator could cause it is if it is putting out AC voltage.

Put your voltmeter on the battery with the engine running and check for AC voltage at the alternator.

Roy

I will check. Is it possible for the ECM to command the alternator to output too much voltage? I am just trying to figure out why my new alternator is no longer working properly.

Yes, it is. You would need a scan tool that can read the PCM and see if it is commanding on the alternator.

Either way, the voltage regulator is inside the alternator and that is no good since the voltage is way high.

Roy

Attached is a live readout of power output. As you can see, the range is 13.595 volts to 16.1 volts on a five mile drive around the neighborhood. Lights, radio and A/C were on. This reading is in sync with my meter readings at the alternator itself. AC output was present, but very low. It fluctuated between 1/4 and 1/2 a volt.

Does this mean that a new alternator with less than 3,000 miles on it has a bad regulator or could it be that the ECM is commanding that much output? Until the voltage output issue is diagnosed, I think every other code is suspect.

Given this new data, what do you think?

You need a new alternator. There should be 0 AC volts. You have a bad alternator.

Roy

Thanks Roy!

You are welcome.

Always glad to help.

Roy

Replaced the alternator. The thing makes noise. Sounds like bearings. Cheap Chinese-made junk. Looks like I will have to replace it again. "DuraLast" is a misnomer. :(

I am still concerned about that wire that hangs off the negative terminal of the battery. It must go somewhere and it is not long enough to attach to anything except the wiring bundle directly behind it. I flushed all of the codes out of the computer. Let's see what else shows up over the next day or so.

Yes, I would try another brand alternator. Have them upgrade you to a better alternator.

Roy

This is the never ending story of a car "ghost" that refuses to go away.

Bought the car in November 2017. A couple of weeks after I got it, the car start intermittently slipping gears. No real pattern of when. It just happened. One time it went into limp mode.

Fast forward to the summer of 2018. I get a charging system error and the car shows all signs of a bad alternator.

I install a new alternator - magic. The problem stops for a considerable number of miles - probably 3,000 and then it starts up again. Test the alternator and it is throwing out over 16 volts, so bad voltage regulator, right? Replaced the alternator again. Now all heck is really breaking loose. I am getting the following codes:

P1719
P0700
P0403
P0405
B2645
B3155
C0561
P1779

In addition to the transmission slips, it seems like the engine is revving too high. When I am at a light, it feels like my foot is lightly on the gas pedal. If I shift into neutral, RPM's briefly increase by 600 RPM's and then they go back to normal. When I shift into reverse, I can feel it wanting to bolt backwards and the car rumbles a bit.

I suspect that this is all electrical and related to one or two specific things. I am just stumped as to which ones.

I am getting about 15.5vdc on my Fluke at the battery. I am also attaching snapshots of the report and the live computer feed.

Help!

Good morning.

The first thing I would do is to check the voltage at the battery again. This time check for any AC voltage on your meter. If you have any AC voltage, the alternator is no good. The modules do not like AC voltage and do not know what to do with it when they see it and will set many codes and the system will act very strange.

The PCM does turn the field control on and off on the alternator and that needs to be checked as well. See if your scan tool can see the command on the alternator.

Roy

Does that include even trace amounts of AC power? I get, at most, .030v of AC at the battery. I have read that trace amounts are okay. Maybe that is wrong. I do not know. Could that loose wire account for these issues? I do not have problems replacing parts. I just do not want to keep taking shots in the dark.

As always, grateful for your advice.

Any AC volts is no good. Whoever said a little is okay is wrong.

Loose connection would stop it from charging, not allow it to overcharge.

Roy

Update: I went to check the car tonight and the battery is dead. Not enough power to even open the door. Did not have any lights on, so I am not sure what could have caused the drain. Should I manually charge up the battery and then test to see if the battery is still good? I know it was hit with over-voltage for some time, as well as some trace AC volts.

I am no longer messing around with the cheap AutoZone alternators. I just ordered a new AC Delco. Hopefully it will arrive this week. I also ordered a new belt and tension-er. That should take the alternator out of the equation.

Good move.

Yes, charge the battery and test it to see if it holds a charge.

Roy

https://www.2carpros.com/articles/car-battery-load-test

https://www.2carpros.com/articles/how-to-charge-your-car-battery

Do I have to do all that, or can I simply use my battery load tester? Is the test you linked me to more accurate?

Use your load tester.

Roy

Okay, new good alternator is in. Battery is okay.

Still get slips on transmission, although its constant now.
Engine idles roughly.
Car "rumbles" when I put it in reverse
Car applying too much power to forward gears - when I take it out of gear and put it in park, the rpm's "surge" briefly to about 2100 before returning to normal.

I cleared the codes to get a fresh set of readings. The last batch of codes that I posted here were present before I cleared them.

Does this mix of symptoms sound more like a bad EGR valve or a bad ECM?

Do you have any codes?

Do you have a scan tool to see what the command is for the idle air control or the EGR valve?

Roy

Took it to the shop this morning. My assistant spoke to the guy later in the day and he said that, in his opinion, the transmission was shot. I have not spoken to the mechanic personally (I will do that tomorrow), but that does not sound right to me - especially as a replacement alternator caused all transmission symptoms to cease for 3,000 miles. When that alternator's voltage regulator caused the voltage to spike to over 16 volts, I assumed that the ECU may have taken a hit and that caused the variety of symptoms I am having now.

What should I ask my mechanic tomorrow if I believe that their diagnosis of a bad transmission may be wrong?

Ask the tech how he determined that the transmission was shot. In order to make that statement, he needs to back it up with test results. Otherwise, he is just guessing on your dime. very expensive guess.

Ask for results of his diagnostic. Also, tell him if you approve the repair and it does not fix the car, you will not pay him for the job.

Roy

Thanks Roy,

Just so I am armed with information, what a the typical tests that would diagnose a bad transmission? Is the any way, if we accept my theory of a computer issue, to prove that it is the computer and not the transmission?

He needs to do a pressure test on the transmission. There are several ports to test main line and clutch application pressures.

As far as the TCM, he needs an advanced scan tool to monitor the readings. If the reading are not there or no communication, it may or may not be the TCM.

Roy