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Battery Light and P0625 code

52K views 14 replies 5 participants last post by  usaf.sully 
#1 ·
Went to start the truck last Saturday after it sat for a week. Truck cranked right up with no signs of a weak battery. Pulled out of driveway and battery light came on. Drove only about 2 miles with AC running on high. Parked, turned off truck. About a hour later went to start her back up and dead. Completely dead. Not even a clicking when turning key. So I jumped it and took it for a nice ride with AC, lights radio, etc all off.


Battery light still on, but appears to be charging, because since that episode it never died on me again.


What I have done since:
1. Check codes - It is indeed the P0625. I cleared the code and it came right back upon next start up. Have done this a few times.
2. Tested the batteries with a multimeter:
engine off = 11.45 volts
engine on and revving slightly with all electronics off ~ 12.50 - 13.50
3. Plugged in Gearbox Z Electron tuner to get some readings. While driving on highway it will read as high as 14.3 V with electronics off. With AC and lights on it will drop to about 12.3V.


I appear to be charging quite well. I have not had dead batteries since that one episode, but the battery light and code stay on.


I have read other posts and it appears this means a bad or dying alternator. But if that was the case wouldn't I not be charging at all?
 
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#2 ·
P0625 indicates the Field/sense circuit is low. The diagnostics for this code can get involved. The most common issue I find with 2008-2010 trucks is the alternator harness chafes on the air conditioning line or another harness in that area. I would access the wiring for the alternator and inspect it very carefully before going nuts or throwing an alternator at it. The red wire at the regulator connector should be equal to battery voltage. A fault like this commonly begins as an intermittent concern and can actually cause an overcharge condition but you seem to have low readings. Start by looking at that harness...
 
#15 ·
I have a 2017 F350 6.7L. I have a battery indicator on my dash that shows up after a minute or 2. No check engine light. Pulled the codes and it's showing P0625 (Generator Field/F Terminal Circuit Low). No other codes. Battery voltage is HIGH.... Between 14.7-15 volts.

Replace the 3 wires (between PCM plug and generator)?

Thanks for any suggestions!
 
#3 ·
Thanks doc. I'll inspect all surrounding wires. But when you said the red wire at the regulator connector can you be more specific? There are 2 places where wires connect to the Alternator. If I am looking at it from the passenger wheel hub, there is a connection at the top and on the left. Is the red wire you refer to the one on the left? And does it require removal to check to see if voltage is same as battery?
 
#4 ·
Do you have single or dual alternators?

There is one LARGE red wire by itself which is the main battery lead. The small red wire is in the 3-wire connector at the alternator.
 
#5 ·
Single. I cleaned up all connections to the battery terminals. Inspected all wires. All look good. But still no resolution.
 
#6 ·
Any Resolution?

Getting the same battery light and code. Battery voltages not running D/S 12.2 P/S 12.1. Field wire at alternator 12.2. While Running I get 14.4 at the battery and it is constant no matter what load or rpm. So I pulled the alternator (Original OEM) and had it tested seven times at three different locations, All passed. Tested batteries, P/S was bad and the D/S was borderline. SO I have two new OEM batteries.

So I decided to look at the starting sequence. The battery light does not come on immediately. So voltage at battery not running 12.5 Turn key to on. Glowplugs on voltage at 12.0. Turn to start voltage drops to 11.8 and engine starts just fine. After 30 seconds battery light comes on and voltage is only 13.0. Then at one minute and ten seconds the voltage jumps to 14.4. This happens at every start...

SO I have looked at a number of websites... "bad alternator if the voltage is greater then 13.8 at an idle with no load.", "got to get a OEM alternator or battery light will not go off", "worn wires around the A/C lines", So without spend Significant Dollars(SD) what would be causing the delay in the voltage increase at the startup?
 
#7 ·
So without spend Significant Dollars(SD) what would be causing the delay in the voltage increase at the startup?
Glow plug operation. Depending on the conditions when the truck is started, the glow plugs usually are on longer than the glow plug light on the instrument cluster is on. Did you test the voltage at the small red wire on the 3-wire connector?
 
#9 ·
So I came up with a wiring diagram that matches the wires I have at the alternator. Since the small red wire at the connector is seeing the same voltage as the big red wire at the back of the alternator, the fusable link is good. So I am assuming that my alternator is charging the batteries just fine, but the sensing lines to the PCM are faulty. What should the voltage reading be at the Violet and Blue/Orange wires at the 3 wire connection?
 

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#10 ·
So here is the results:
(Status)(Violet Volts)(Blue/Orange Volts)
Key Off Engine Off 0V 12.2V
Key On Engine Off 0V 0V
Key On Engine On 0V 4.0V

Turned off everything and measured for grounds.
Pulled the 3 wire connector. No Grounds on all six connections, Alternator side or Connector side.

This leads me to the Alternator may test good and put out a charge, but the Violet wire is not sending anything to the GENMON in the PCM so the battery light is coming on. ie: the voltage regulator of the alternator is bad.

Next Question: Aftermarket Alternators: Looking at O'Reilly's Auto: Ultima Reman or Ford OEM New?
 

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#12 ·
Did some internet searching this morning and came up with this.... I think it is a good explanation of the GENCOM and GENMON.

Ford Application: Alternator GenCom and GenMon Signals | Remy Auto Parts

GenMon is the alternator load information provided to the PCM by the regulator. The voltage source for the signal originates at the PCM, and the regulator modulates the signal to ground with a variable duty cycle signal. The signal is approximately 128 Hz, but varies based on specific regulator. The duty cycle command varies from 5 - 95%. The higher the duty cycle, the higher the load. GenMon should have a signal anytime the alternator is operating. •With the key in the off position, disconnect the 3-pin regulator connector, turn the key to the on position, and measure voltage on the GenMon pin of the wiring harness connector, (Figure 2). The voltage should be near battery voltage. If voltage is low check the GenMon circuit for short to ground or high resistance short. If the harness checks ok, the PCM is likely failed.
•Turn the key off and reconnect the regulator connector. Carefully backprobe the GenMon terminal (Figures 1 & 2). Start the vehicle and monitor the duty cycle and/or voltage. There is no fixed value—it is dependent upon battery SOC and vehicle loads. Once the vehicle has stabilized, add loads. The duty cycle and/or voltage should rise. Turning off loads should result in a decrease. ◦If the duty cycle and/or voltage do not rise and fall with corresponding changes in loads, inspect the alternator connector, verify alternator power and ground circuits, and replace the alternator.
 
#13 ·
SO I feel like I am talking to myself, but at least everything is written down in one place.

So as determined the alternator was not sending out a GENMON signal back to the PCM. Therefore the battery light was on. So I purchased the Ultima Reman Alternator from O'Reilly's Auto and installed it.


As before the voltage at battery not running 12.3 Turn key to on. Glowplugs on voltage at 11.9. Turn to start voltage drops to 11.6 and engine starts just fine. After 30 seconds the battery voltage is only 13.0, BUT NO BATTERY LIGHT. Then at one minute and ten seconds the voltage jumps to 14.5.

As for the standard stuff, Yes I removed the passenger side wheel well cover. That was the easiest way. As for the belt tensioner, I have a 3/8 drive Craftsmen ratchet that has a flat handle and was only about 6" long. I drilled a hole in the handle. Reaching in from the side or bottom I placed the ratchet on the tensioner. Then I hooked a ratchet strap to the handle and to the frame/axle.( what ever was inline with it.) That kept the belt loose and I was able to easily remove the belt from the alternator.
 
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