High Voltage Culprits? - JeepForum.com
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post #1 of 30 Old 09-28-2019, 06:13 PM Thread Starter
FireMedic82
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My idling voltage is 15-15.1 and I'm trying to determine how to go about confirming my PCM as the culprit before I go throwing parts at it and altering my wiring. So far, I've done a drop voltage test on my starter ground and alternator ground, checked for wiring shorts, and finally stopped by a parts store to have my battery and alternator checked. All of that came back showing no issues.

It was mentioned to me that I could have a bad diode in my alternator, but I'm not sure where to go with that suggestion, aside from pulling it apart to test diodes.

Can anyone tell me how I can confirm my PCM as being the problem?

On a side note, it hasn't thrown a code, and I haven't noticed any mechanical problems as a result. I also saw it mentioned in the FSM that 16 volts is basically the point where voltage should be a concern, but others are reporting with voltages ranging from 13.5 to 14.5.


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post #2 of 30 Old 09-28-2019, 06:34 PM
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Are you just going off of the cluster voltmeter or is the reading corroborated with a test meter at the alternator output or across the battery terminals while the engine is running?
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post #3 of 30 Old 09-28-2019, 07:11 PM Thread Starter
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All done with a test meter. Straight off the battery posts I'm seeing 15-15.1 with all non essentials turned off.

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post #4 of 30 Old 09-28-2019, 08:02 PM
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You might try getting the battery load tested. If the battery is faulty the voltage regulator may be trying to charge the battery with full voltage output in a valiant but futile attempt to bring it up to full charge.

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post #5 of 30 Old 09-28-2019, 08:43 PM Thread Starter
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Originally Posted by JFM626 View Post
You might try getting the battery load tested. If the battery is faulty the voltage regulator may be trying to charge the battery with full voltage output in a valiant but futile attempt to bring it up to full charge.
I tested it with the multimeter and the voltage was above 10. It's been a couple of weeks since, so I can't recall the exact voltage. Definitely between 10 and 11 volts.
The guy at the autoparts store did one there too. He said everything checked out good.

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post #6 of 30 Old 09-28-2019, 08:50 PM Thread Starter
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It seems like I recall reading in one of these forums that the field wire itself could be a cause for overcharging. The path is pretty short though, isn't it? I haven't pulled wiring from the factory looming, but I wouldn't suspect a short. Maybe at the connector? Not really sure what to test for at the connector, aside from continuity and a visual inspection. If I look into that, is there anything I'm missing?

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post #7 of 30 Old 09-28-2019, 09:37 PM
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Electronic voltage regulator function from the FSM:
"The amount of DC current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series with the generators second rotor field terminal and its ground. Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature (refer to Battery Temperature Sensor for more information). It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 100 times per second (100Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output."

Battery temperature sensor info:
"The BTS is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures. The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases and the detection voltage at the PCM increases."

The fact no codes are being thrown makes me think the PCM believes the charging system is working as it should. If the cluster voltage reading and test meter readings are the same, I would suspect either the fused battery (B+) voltage to the PCM which the EVR is using as a baseline is low (corrosion, poor connection, etc), or the BTS voltage is reading abnormally high so the PCM thinks the temp is colder than what it is in reality.

A shorted generator field wire would normally result in a voltage output that steadily increases to a very high level as engine speed increases, not to mention a P0622 or similar fault being thrown.

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post #8 of 30 Old 09-28-2019, 09:47 PM
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I can't offer any insight into why it's overcharging, but you can run an external voltage regulator rather than replacing the PCM, if it comes down to that. There was a recent post that Standard Motor Products VR125T Voltage Regulator and S572 Pigtail/Socket cured an undercharge issue on an '05 TJ.
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post #9 of 30 Old 09-28-2019, 11:23 PM Thread Starter
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Quote:
Originally Posted by mukluk View Post
Electronic voltage regulator function from the FSM:
"The amount of DC current produced by the generator is controlled by EVR circuitry contained within the PCM. This circuitry is connected in series with the generators second rotor field terminal and its ground. Voltage is regulated by cycling the ground path to control the strength of the rotor magnetic field. The EVR circuitry monitors system line voltage (B+) and battery temperature (refer to Battery Temperature Sensor for more information). It then determines a target charging voltage. If sensed battery voltage is 0.5 volts or lower than the target voltage, the PCM grounds the field winding until sensed battery voltage is 0.5 volts above target voltage. A circuit in the PCM cycles the ground side of the generator field up to 100 times per second (100Hz), but has the capability to ground the field control wire 100% of the time (full field) to achieve the target voltage. If the charging rate cannot be monitored (limp-in), a duty cycle of 25% is used by the PCM in order to have some generator output."

Battery temperature sensor info:
"The BTS is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures. The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases and the detection voltage at the PCM increases."

The fact no codes are being thrown makes me think the PCM believes the charging system is working as it should. If the cluster voltage reading and test meter readings are the same, I would suspect either the fused battery (B+) voltage to the PCM which the EVR is using as a baseline is low (corrosion, poor connection, etc), or the BTS voltage is reading abnormally high so the PCM thinks the temp is colder than what it is in reality.

A shorted generator field wire would normally result in a voltage output that steadily increases to a very high level as engine speed increases, not to mention a P0622 or similar fault being thrown.
That's awesome, mukluk. Thanks for digging into all of that info. My vague recollection of hearing about the field wire makes sense now. Your suspicion with the input voltage makes sense. So, that I need to check. The BTS part of it is a bit confusing. It seems with it being as hot as it has been this summer, that it would be warm enough to keep it from misbehaving. Most especially after the motor has been running for a while. Either way, that's worth looking into while I'm in there. I suspect the motor was removed prior to me buying it, so now I'm wondering how the PCM would react to the BTS not being connected.

Maybe I can get in there and check these tomorrow. When I do, I'll let you know how it turns out.

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post #10 of 30 Old 09-28-2019, 11:26 PM Thread Starter
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Quote:
Originally Posted by AjRagno View Post
I can't offer any insight into why it's overcharging, but you can run an external voltage regulator rather than replacing the PCM, if it comes down to that. There was a recent post that Standard Motor Products VR125T Voltage Regulator and S572 Pigtail/Socket cured an undercharge issue on an '05 TJ.
Thanks, AJ. Yeah, I've got an external setup just in case. Not wanting to bypass or alter wiring just yet.

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post #11 of 30 Old 09-29-2019, 07:26 AM
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After reading mukluk's post I have to ASK
Did OP use a scanner to check codes? I did not read about OP checking.
What does the PCM see as voltage from battery? A skewed reading her would have it overcharging.

PS - I have NOT seen a solution to a constant CEL with external regulator. ANYONE know of a fix for CEL with bypass?

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post #12 of 30 Old 09-29-2019, 09:01 AM
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Quote:
Originally Posted by FireMedic82 View Post
I tested it with the multimeter and the voltage was above 10. It's been a couple of weeks since, so I can't recall the exact voltage. Definitely between 10 and 11 volts.
The guy at the autoparts store did one there too. He said everything checked out good.

Wait, you're saying that the battery voltage with the battery disconnected from eveything is between 10 and 11 volts?


If so, your auto parts guy is an idiot(or possibly reading the surface charge generated on your drive to the store). Fully charged voltage of the battery alone should be around 12.6v.


Methinks JFM626 may be right about the computer trying to keep a dead battery alive.
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post #13 of 30 Old 09-29-2019, 09:18 AM
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I agree with above - if eng off and battery voltage is that low. BATTERY time.

AGAIN reading long posts shows My reading comprehension SUCKS.

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post #14 of 30 Old 09-29-2019, 01:26 PM
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Quote:
Originally Posted by jtec View Post

PS - I have NOT seen a solution to a constant CEL with external regulator. ANYONE know of a fix for CEL with bypass?

This company has a Field Replacement Module (FRM) option but some have reported using their regulator kit & not getting the CEL without the FRM. I can probably find & link something on that if needed.

http://alternatorparts.com/external-...nator-kit.html
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post #15 of 30 Old 09-29-2019, 02:05 PM Thread Starter
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Originally Posted by jtec View Post
After reading mukluk's post I have to ASK
Did OP use a scanner to check codes? I did not read about OP checking.
What does the PCM see as voltage from battery? A skewed reading her would have it overcharging.

PS - I have NOT seen a solution to a constant CEL with external regulator. ANYONE know of a fix for CEL with bypass?
I haven't used a scanner. I've always used the Jeep's built in method. That's one that I haven't checked. After hearing from mukluk last night, I plan to check that.
After I thought about it a little more, I'm not sure exactly how to check that. Maybe I'm overthinking or missing something, but if the PCM regulates by cycling the ground, how do I test to see what voltage it's seeing? Or is it the ground wire only that the PCM is cycling through and the voltage can be tested by checking the field wire?

As for the CEL, the kit that Rubi4MyMrs mentioned is the only one I've heard of also. I did read somewhere from that company that the module has turned the CEL off in most cases, but not all.

Throw the photoshoppers a bone and post your executed mods, we would like to see the after pics. Copy and paste the url. https://www.jeepforum.com/forum/f59/executed-photoshop-mods-1417032/
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