Alternator check

[mike_b]

Hi. I own a 2006 TJ 4.0, and recently the check gauges light came on, intermittently at first, but now it turns on a few seconds after I start the engine. Doing the ignition key thing to get error codes, I see code P0622. The battery gauge shows on the dashboard shows approx, 12V. I checked the voltage of the (relatively new, 2 years) battery directly, it was 12.07 V after driving with the check gauges light on for a few miles. I then checked the voltage with the engine running, and it dropped to 10.7V (on the battery). Next, I tested the F-terminal with running engine. The hot lead on the connector (disconnected from alternator) shows 10.7V. no fluctuations (running on idle). I did take a look at the wires. Although the plastic cover around the wires is a bit brittle and failing, I did not see any indications of chafing on the wires or any brakes that could lead to shorts or disconnections.

I saw somewhere on a youtube video that if you see a light when testing the F-terminal (meaning there is a connection to the PCM), but the alternator is not changing or throwing a P0622 code (which I do see), it is a bad alternator.

Is that true? Is voltage of 10.7V on the hot lead of the F-terminal normal?

 

[Ashim]

Alternator is bad.

 

[OldBuzzard]

The voltage regulator is in the PCM. I believe it sends a PWM (squarewave) signal to the field of the alternator to control output voltage. So a reading of the F terminal with a volt meter might not tell you too much. An oscilloscope would give a lot more information, but of course not everyone has one in their pocket.

The problem certainly could be a bad alternator, but it also might be a bad PCM or a bad battery temperature sensor.
Sorry, but I'm not sure where to start on testing.

 

[mike_b]

Thanks, everybody. I think I will just get a new alternator and see if that fixes the problem. I know that the stock alternators are rated for 90 A. Is it worth to get a more powerful one? I don't have any power-hungry accessories, except for a bass-booster. Any suggestions for a good brand?

 

[KennethS]

Most auto parts stores can test the alternator. Doing that might help isolate the problem.

 

[Cooper Smith]

Hi. I own a 2006 TJ 4.0, and recently the check gauges light came on, intermittently at first, but now it turns on a few seconds after I start the engine. Doing the ignition key thing to get error codes, I see code P0622. The battery gauge shows on the dashboard shows approx, 12V. I checked the voltage of the (relatively new, 2 years) battery directly, it was 12.07 V after driving with the check gauges light on for a few miles. I then checked the voltage with the engine running, and it dropped to 10.7V (on the battery). Next, I tested the F-terminal with running engine. The hot lead on the connector (disconnected from alternator) shows 10.7V. no fluctuations (running on idle). I did take a look at the wires. Although the plastic cover around the wires is a bit brittle and failing, I did not see any indications of chafing on the wires or any brakes that could lead to shorts or disconnections.

I saw somewhere on a youtube video that if you see a light when testing the F-terminal (meaning there is a connection to the PCM), but the alternator is not changing or throwing a P0622 code (which I do see), it is a bad alternator.

Is that true? Is voltage of 10.7V on the hot lead of the F-terminal normal?

Get the alternator tested before replacing it. They're expensive enough to warrant pulling it off and taking it in to verify.

 

[Badgerbiter]

I don’t want to hijack the thread, but is it a bad thing in the collective wisdom of this forum to replace the stock alternator with a larger rated alternator? I am kind of jonesing for more amperage for winching and such!

 

[CharlesHS]

This problem could be as simple as the ECU is not receiving a signal of system voltage which tells the ECU internal voltage regulator to charge the battery and supply power to the electrical circuits.
I would disconnect the four 32 pin harness connectors, verify the pins and clips are not oxidized (clean if necessary) or melted and firmly reattach the harness connector into the ECU receptacles.
Test to see if the alternator starts charging again.

 

[KennethS]

I don’t want to hijack the thread, but is it a bad thing in the collective wisdom of this forum to replace the stock alternator with a larger rated alternator? I am kind of jonesing for more amperage for winching and such!

Larger just gives more capability. If your vehicle needs 40 Amps and you originally had have a 60 Amp alternator, then replace it with a 100 Amp alternator, the vehicle still draws 40 Amps. The 100 Amp alternator just gives the ability to supply more, if the vehicle needs it.

So to answer your question, no it’s not a bad thing, it’s just more expensive.

 

[JKP]

Thanks, everybody. I think I will just get a new alternator and see if that fixes the problem. I know that the stock alternators are rated for 90 A. Is it worth to get a more powerful one? I don't have any power-hungry accessories, except for a bass-booster. Any suggestions for a good brand?

Stock is 117A, and most any auto parts store can test the alt.

 

[macleanflood]

Go with Denso if you can.

-Mac

 

[mike_b]

Thanks everybody. I decided to get a new alternator with the same amperage as the old one. Got it yesterday and replaced the old one. Half an hour later, my voltmeter shows 14+ Volts, and the error message has disappeared.

I also noticed a few drops of red liquid right under the steering wheel fluid container. After a bit of spelunking under the car, I noticed that the hose clamp for the low-pressure return line was quite loose. Tightening the clamp stopped the dripping, and as a bonus also stopped the annoying whistling I had when the engine was running just above idle, and where I could not find an issue in the vacuum system. Would have never suspected that.

So, all around a good day. Several problems solved.