05 TJ Charging issue - JeepForum.com
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post #1 of 31 Old 05-22-2020, 09:47 AM Thread Starter
pamante
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05 TJ Charging issue

HELP!

I have on 05 TJ with the 4.0L and an AT. Completely stock. No mods. The battery was replaced in January and the alternator a few days ago. The check gages light came. Changing the alternator didn't help. I watched the guy at Advanced Auto test the new one - fine. Alternator output at idle is 11.6 volts at the alternator with my multi-meter no accessories on. Same reading from my scan tool with the engine at 2000 RPM.

No Codes from the ECU. Is the alternator controlled by the ECU? The ECU was replaced a few years ago. I also noticed the brake fluid level light came on even though the fluid was full. I discounted that as not a big deal. Now I'm wondering if the ECU is dying.

Any help would be appreciated.

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post #2 of 31 Old 05-22-2020, 09:54 AM
jtec
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autozone said 11.6v was OK?

Lets start simple easy, engine off check and record -
voltage at battery,
voltage at alternator.

Start engine repeat.
V at battery.
V at alt.

you did use scanner to check codes?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #3 of 31 Old 05-22-2020, 01:05 PM
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Quote:
I also noticed the brake fluid level light came on even though the fluid was full.
No TJ came with a brake fluid level sensor or low level light. The brake warning light is a hardwired indicator which doesn't have anything to do with the PCM, it should only illuminate if the instrument cluster receives a ground signal from the parking brake switch or the brake master cylinder combination valve.

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post #4 of 31 Old 05-22-2020, 03:39 PM
Vinman
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First thing I would do is confirm the positive battery cable and all the ground wires/cables have a good connection.
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post #5 of 31 Old 05-22-2020, 04:41 PM Thread Starter
pamante
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Thank you for the responses

Battery cable are clean and tight
I checked for codes with a scanner (Innova 6100P)

Engine off
Voltage at battery 12.12v
Voltage at alternator lug 12.11v

Engine at idle - no accessories on
Voltage at batter 11.66v
Voltage at alternator lug 11.66v

Can anyone shed some light on whether or not the ECU controls the alternator?

Thanks
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post #6 of 31 Old 05-22-2020, 04:56 PM Thread Starter
pamante
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Forgot - the testing unit at Advanced Auto only showed pass / fail - not actual voltage.
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post #7 of 31 Old 05-22-2020, 06:03 PM
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Quote:
Originally Posted by pamante View Post
Thank you for the responses

Battery cable are clean and tight
I checked for codes with a scanner (Innova 6100P)

Engine off
Voltage at battery 12.12v
Voltage at alternator lug 12.11v

Engine at idle - no accessories on
Voltage at batter 11.66v
Voltage at alternator lug 11.66v

Can anyone shed some light on whether or not the ECU controls the alternator?

Thanks
The alternator's voltage regulator is contained within the PCM, yes.

Your readings point toward the Jeep running entirely on the battery, the alternator is not charging. You should be getting a fault code or two pertaining to the charging system, though the less than 50% charge battery may be causing the PCM to not store any. Assuming the battery cable connections at both ends of the cables are clean and tight, you should probably take a look at the two field wires and their connections running between the alternator and PCM (the two smaller wires connected to the alternator, not the thick red one).

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post #8 of 31 Old 05-22-2020, 06:14 PM Thread Starter
pamante
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I agree. If I charge the battery I can get a few miles from the house before the "Check Gauge Light" comes on. I checked the wires at the connector on the alternator and they look fine. Not looking forward to tracing them back to the ECU. So does the ECU manage the alternator and tell it when to charge the battery?

Thanks
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post #9 of 31 Old 05-23-2020, 07:57 AM
Strangers
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Pamante, the short answer is yes. but if you have connector and or wiring issues the PCM/ ECU won't know that. so eliminate that first. I've seen people throw an alternator at the problem and still have zero charging.

Me, Banditt, Tippie and ole Heep a long!
RIP Banditt 3/86 - 11/01
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post #10 of 31 Old 05-23-2020, 09:02 AM Thread Starter
pamante
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Thanks for the response

Unfortunately that is exactly what I did. I have checked everything I know how to check. All the grounds, body and chassis have been cleaned and verified. Battery cables look good and are tight. I checked the battery temp sensor resistance. The only thing I haven't checked is the field wires from the alternator to the ECU. I haven't been able to find which connector and pins they are on the ECU.
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post #11 of 31 Old 05-23-2020, 09:24 AM
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do testing BEFORE jumping to condemn PCM.
If the PCM is NOT seeing correct voltage on field driver it should code.
SO are there ANY codes ? ANY?

The key ON there shouold be 12v both wires of field.
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When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #12 of 31 Old 05-23-2020, 09:58 AM Thread Starter
pamante
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Thanks

No error codes stored in the computer memory. Used enhance OEM scan
Key on - engine not running
No voltage in either wire in the field connector at the alternator.
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post #13 of 31 Old 05-23-2020, 10:26 AM
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no voltage at either field wire - only 1 is 12v from the PCM the other (driver) is the ground.

There is some testing needed - unplug the alt and see if the system sets a code - P0622 -
Also check probe the wires upstream from connector or atb the PCM .


Is there a remote starter?

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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post #14 of 31 Old 05-23-2020, 10:46 AM Thread Starter
pamante
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I appreciate your help.

No codes after starting with the field wires disconnected. Which ECU connector and Pins? Is it Pin 10 and 25? I have the wiring diagrams but it isn't obvious which connector
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post #15 of 31 Old 05-23-2020, 10:59 AM
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above shows C2 and C3 the terminals are C2 -10, C2- 25 douuble check dia I don't have glasses on

If you have the manual look at pinouts for PCM C2 and C3

When I see the price of OEM I think aftermarket.
When I see the quality of aftermarket I think OEM.
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