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Randall C
Randall C, ASE Master Technician
Category: Dodge
Satisfied Customers: 12827
Experience:  ASE Master Tech, 32 years Diag/Electrical Specialist
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92 dodge dakota: v6..The alternator..check engine light..fault codes

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I have a 92 dodge dakota, v6. The alternator is not charging the battery, the check engine light is on. I check for fault codes and it showed fault 41- charging system excess or lack of field current. I checked the terminals on the alternator, the heavy cable reads 12 volts, and one of the two smaller wires reads 12 volts, the other smaller wire has 0 volts.

Tracer :

Hello, is it charging at all or no charge?

JACUSTOMER-jmnl7vnp- :

It is not charging at all.

Tracer :

Ok, alt tested ok, new battery etc and code 41? what many people do not know is that Dodge is a bit unique in that the alternator usually does not fail but the vehicle computer does. The charging system/regulator is 100% controlled by the engine computer,. the fact you have the light and code 41 leads me to bad charging circuit within computer. this was/is very common. we have replaced many computers over the years on these engines. here is the formal description via the shop manual.Coming next

Tracer :

Voltage regulation is necessary on all vehicles that have a charging system with an alternator. All voltage regulators limit the voltage the vehicle's charging system produces. The need for this regulation is most critical on vehicles with electronic devices, such as an engine controller, body controller, or ETR radio. Inconsistent voltage levels or excessively high or low voltage levels have a negative effect on the performance and durability of electronic components.

There are two basic functions of a voltage regulator:

  1. To maintain a constant system voltage regardless of the vehicle's electrical load requirements or its engine speed.
  2. To regulate system voltage to keep the battery at an optimum state of charge.

The engine controller contains the voltage regulator function. The engine controller uses the battery voltage sense, the battery temperature sensor, and its own program to determine the charging system's voltage goal. The voltage goal is adjusted by the controller based on changes in the voltage sense and temperature values.

The basic voltage regulating function is to keep the charging system voltage between 12.9 and 15.0 volts. The voltage regulator accomplishes this by controlling the current flow through the rotor. Since the rotor is electromagnetic, controlling the current through the rotor effectively limits the strength of the magnetic field and the output of the alternator.


JACUSTOMER-jmnl7vnp- :

Any suggestions for a source of aftermarket ECUs?

JACUSTOMER-jmnl7vnp- :

Would an after market ECU be Ok? I am sure the dealer's cost would be more than the vehicle is worth.

Tracer :

let me check and see what the ECU runs . Back shortly

Tracer :

is your truck auto or manual trans? also, is it in california?

JACUSTOMER-jmnl7vnp- :

it is manual and not in california

Tracer :

Autozone has good price between $155 and $197. the $155 is with auto trans and trade in your computer. $197 is with manual trans and trade in your computer

Tracer :

manual is the higher price unit but $200 at autozone not bad. A good alternator can run that much and new not reman

Tracer :

Dealer I think is in the $500 range but... theirs is new NOT reman

Tracer :

Reman is just fine

Tracer :

Unfortunatley, the ECU can not be repaired just for no charging, has to be replaced as whole unit

JACUSTOMER-jmnl7vnp- :

Thanks for your help.

Tracer :

You are welcome. Sorry its not the best news but.. with this system, it can be a bit costly. 99% of the time is the computer

Randall C and 4 other Dodge Specialists are ready to help you
Customer: replied 6 years ago.
A strange thing happened. I reconnected the wires to the alternator and it is now charging. This has happened before, when I took the alternator off to have it tested and then reinstalled it, it worked fine for a few weeks and then quit working. I noticed that the two smaller wires (I assume they send power to the field windings) go through a small plastic box that is attached to the alternator. A heavy gauge wire also passes through the box and then attaches to the alternator case. Any idea what the little box does?
I suspect you are kind of resetting the ECU when you unhook and rehook. The black box you see really does nothing but contains all the connections in one spot. I put diagram below. You will see that the Green wire from that black juction does go to computer. You will NOT see voltage on that wire as its computer/regulator sense only. I cant rule out bad connection but I have not ever run into one of the juction blocks you describe being bad

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Customer: replied 6 years ago.
Thanks for the additional information. I will replace the ECU.
Sorry for delay. Sometimes we have banged hard on the ECU while watching a volt meater hooked to battery to see if the charging kicks back in while hitting hard on ECU. A shop can hook up scanner and read some ECU data to confirm bad if you want further test before replace. Good luck with it. Thanks again
Customer: replied 6 years ago.
I will give that a try. Thnaks.

Can we tackle another unrelated problem with this vehicle, or do I need to start a separate session?

depends, rules are for one question but shoot, I will see what i can do/ LMk thanks
Customer: replied 6 years ago.
The vents for the AC system stop blowing air when the engine is under a load (it seems like sometimes the air comes out the lower vents). They work fine at idle. I checked engine vacuum and at idle it is 17 in Hg, steady. We live in Phoenix and its a pain without AC.

I don't mind paying for another session if that is the rule.
It sa vacuum problem. Either leak or bad check valve from canister to inside vehicle. let me check some things and get back with you but will be a little bit as i am just starting dinner. Give me a bit and I will see what i can do to help direct you as to what to check. back shortly.
Customer: replied 6 years ago.
No Hurry. I forgot to charge the battery, ran an errand, came out from the store and it wouldn't start. So it is sitting across town while the battery is getting charged.

On your truck, you should have a small plastic item called a vacuum check valve located near the brake booster. If the check valve does not work, then the vents will shift around under load. You need to find the vacuum line near booster, look for inkline check valve. It is in the same vacuum line going through firewall from engine bay to inside of vehicle. you should only be able to blow through it one way. see what you can find. LMk thanks


The heater/AC system changes to the defrost mode during a low vacuum condition such as during trailer towing, hill climbing, and acceleration.


1. Connect a test vacuum supply to the vacuum line going to the heater/AC controls.
A. On AB vehicles, locate the vacuum connection in the engine compartment tucked into the wiring harness clip above the middle of the radiator. Disconnect the black rubber source hose going from the engine to the black plastic heater/AC system hose. Connect the test vacuum source to the plastic hose.
B. On all other vehicles, remove the vacuum check valve from the vacuum supply line near the brake booster and connect the vacuum source to the hose going through the dash panel.
2. Pull between 10 and 20 inches of vacuum (Hg.) with the test vacuum source.
3. With the test vacuum source shut off, the vacuum reading should remain constant for one minute.
4. If the vacuum reading dropped within one minute, there is a leak in the system. Locate and repair the leak as outlined in the appropriate service manual before proceeding to the repair procedure.
5. If the vacuum reading remains constant for one minute, proceed to the repair procedure.


1 Valve With Reservoir, Vacuum Check (all Vehicles) (NNN) NNN-NNNN2 Connectors, In-Line (AB Vehicles) (NNN) NNN-NNNNAs Required 3/16" Vacuum Hose - serviced in bulk (AB Vehicles) (NNN) NNN-NNNN


This bulletin involves inspection of the heater/AC vacuum system and installation of a revised vacuum check valve.


1. Locate where the black rubber vacuum source hose connects to the black plastic heater/AC hose. Cut the rubber source hose 2 inches from the connection and install the new vacuum check valve (PN(NNN) NNN-NNNN. If the rubber source hose is small (1/8 inch), use two in-line connectors (PN(NNN) NNN-NNNN and two 2 inch pieces of 3116 inch hose (PN(NNN) NNN-NNNN to adapt the new vacuum check valve to the smaller hose.
2. Trim the vacuum hose so that the new length is the same as the old.
3. Install the vacuum hose back into the wiring clips taking care to locate the check valve where it will not rattle and is not exposed to excessive heat.


1 Install the new vacuum check valve assembly (PN(NNN) NNN-NNNN, in the vacuum lines at the same location as the original check valve. Discard the original check valve.
Reimbursable within the provisions of the warranty. TIME ALLOWANCE:
Labor Operation No. 24-50-47-90...............................0.2 Hrs. FAILURE CODE:
X9 - Vacuum Leak
Notice in diagrams, look for the vacuum source from engine. You will see check valve noted. I think yours gets vacuum from vacuum source off brake booster

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Randall C and 4 other Dodge Specialists are ready to help you
Customer: replied 6 years ago.
thanks for you help