Question about 1997 Isuzu Rodeo

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Alternator drops voltage on accel or when A/C is turned on. Leaning towards PCM if it controls output voltage from the alternator.

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I don't think a 97 is PCM controlled. What I would do is pull the alternator plug. Yours should be two wire(hot and ground). the third single wire plug is for the battery light or meter. Anyway. on the two wire plug check them for power, turn the ignition on and use a volt meter to find the power wire. The other is ground. The voltage should be close the battery voltage. Then I would check the battery grounds. From the battery negative side, there should be one to the engine and one to the body, then one from the engine to the body. These are the main grounds. If they are good, I would cut the ground wire at the alternator (about 4 inches) and run a new ground any where on the engine. This should take care of your voltage lose.

Posted on Apr 04, 2015

Testimonial: "We checked the alt. plug and it had 4 wires. We did however remove the three belts to the crank pulley and found that the outer belt groved ring turned freely from the inner housing. We replaced the harmonic pulley and the problem of the 'squeal' was gone. We did notice however that when the engine throttle was goosed, the voltage still went from 14.44 down to 13.39 (with the A/C on) but recovered bqck to 14.44 and no squeal. I still suspect the ECM plays a role in regulating the voltage from the alternator. Another problem for another day......"


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My battery light came on while i was driving than a few minutes later everything shut off. The battery was replaced in january and alternator was replaced in october.. what could be the problem?

For the alternator to work B+ voltage must be applied to the heavier gage wire on the back of the alternator ,plus the alternator is computer controlled , by the PCM !
Charging System Indicators
BATTERY The IPC illuminates the battery indicator when the following occurs:
The PCM detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the PCM requesting illumination.

The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the body control module (BCM) indicating the system voltage.

The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds.

The ignition is on, with the engine off.
BATTERY NOT CHARGING The IPC illuminates the battery not charging indicator in the driver information center when the following occurs:
The PCM detects that the generator output is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the PCM requesting illumination.

The IPC determines that the system voltage is less than 11 volts or greater than 16 volts. The IPC receives a class 2 message from the body control module (BCM) indicating the system voltage.

Your best is to have a qualified repair shop check it out ! Could have DTC'S - diagnostic trouble codes stored !
DTC P0562
The powertrain control module (PCM) continuously monitors that the system voltage stays within the proper range. If the PCM detects an excessively high system voltage, DTC P0563 will set. A high voltage condition may cause a stalling condition or other drive ability concerns.
DTC P0621
The powertrain control module (PCM) uses the generator turn on signal circuit to control the generator. A high side driver within the PCM allows the PCM to turn the generator ON and OFF. When Generator operation is desired, the PCM sends a 5 volt signal to the voltage regulator via the generator turn on signal circuit. This causes the voltage regulator to begin controlling the generator field circuit. Once the Generator is enabled by the PCM, the voltage regulator controls generator output independently of the PCM. Under certain operating conditions, the PCM can turn Off the generator by turning Off the 5 volt signal on the generator turn on signal circuit. The PCM has fault detection circuitry which monitors the state of the generator turn on signal circuit. If the fault detection circuit senses a voltage other than what is expected, this DTC will set. The voltage regulator also contains fault detection circuitry. If the regulator detects a problem, the regulator will ground the generator turn on signal circuit, pulling the voltage low. This also causes the PCM to set the DTC.
DTC P0622
Checking for codes an voltage drop testing the connections an using a scan tool to check data parameters is the only way to solve your problem . Which means taking to a qualified repair shop !

Jul 26, 2016 | 2002 GMC Envoy

4 Answers

My alternator went out yesterday. I was told that I have a fuse and to check it first but I am unable to locate it in any of my fuse box. Does a 2005 Chevy Impala have an alternator fuse????

The red wire from starter, at the alternator, hot all the time. The orange wire at alternator, hot all the time. Use a test light on those wires, if hot, I don't think it is a fuse? Your owners manual should have the fuse layout.


Nov 01, 2015 | Cars & Trucks

1 Answer

Alternator output 11.9vdc to 12.4vdc. Replaced with new alternator, same output as old. Car will not stay running due to battery running car. Any ideas?

Is there battery voltage at the bigger gage wire on the back of the alternator ? The other wire in the connector is a control feed from the PCM - engine computer , It is marked L ,if you hook a test light to positive battery terminal an touch the other point end to the L terminal an it starts to charge your alternator is not being turned on by the PCM ! Could have open circuit or bad PCM !

Jul 26, 2015 | 1994 Cadillac DeVille

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I have 2003 Saturn Ion and I have bought a new

test the battery voltage while the engine is running, (you'll have to jump it again)
if you know the battery, voltage regulator and alternator are good, you may have to check all the fuse-able links on the car, all the vehicle grounds, and the fuses and relays.
if you put your battery on charge until it is fully charged and let the car sit over night and it is dead, either the battery is internally shorted or the vehicle is drawing far to much current and each circuit tested to find the short.

Oct 01, 2014 | 2003 Saturn ION

1 Answer

I have a 2000 ram 2500 with diesel. The alternator does not have any voltage on the blue wire for postitive excitation. The green wire (negative) will read to battery + so it is okay. I have done a...

The green wire should be your gen field wire not a ground wire. The alternator should be grounded through the alternator. The blue wire should be a feedback to the pcm only when the alternator is charging (engine running). Make sure your main 140amp charging fuse is good. It also has a battery temperature sensor that controls the field to the alternator. Wire 15 on ecm pnk/yellow to wire 4 blk/lt blue (c1 connector). This should be a variable resistor. If you have voltage on the Dk green wire when running but no output, suspect a bad alternator or bad connections going into the alternator. Be cure to test for alternator output on the alternator itself.

Oct 14, 2012 | Dodge Cars & Trucks

3 Answers

2003 windstar alternator over charge I try 5 or 6 alternator diferent companie always the same problem go up to 18.80 v help me please

it should notgo over 14 1/2 volts.

Get free DTC codes scan from Autozone. I think you will get DTC code 1246 - System Voltage Malfuction.

The I (indicator) (BAT light) wire activates alternator field circuit.

The heavy B wire circuit sends current to the battery for charing and to run the car.

The S circuit helps control the amount of charge. I suspect yours is not controlling. This car has the PCM (engine computer) help control the output and turn the BAT light on when under or over charging.

SECTION 414-00: Charging System - General Information 2003 Windstar Workshop Manual
DESCRIPTION AND OPERATION Charging System This vehicle is equipped with a powertrain control module (PCM)-controlled "smart charge" charging system. The PCM-controlled charging system is a system whereby the PCM determines the optimal voltage setpoint for the charging system and communicates this information to the voltage regulator. The PCM-controlled charging system is unique in that it has two uni-directional communication lines between the PCM and the generator/regulator. Both of these communication lines are pulse-width modulated. The GEN COM line communicates the desired setpoint from the PCM to the voltage regulator and the GEN MON line communicates the alternator load condition to the PCM. The third pin on the voltage regulator, the A circuit pin, is a dedicated battery voltage sense line.
  • Charging system malfunction (high or low system voltage)
  • possible causes:
    • A circuit 35 (OG/LB).
    • A circuit fuse link.
    • B+ circuit 36 (YE/WH).
    • B+ circuit fuse links.
    • Generator.
    • PCM
    • GEN-COM circuit 586 (RD/PK).
    • GEN-MON circuit 585 (VT).
    Generator The generator (10300) on this vehicle is monitored and controlled by the powertrain control module (PCM). The PCM monitors the voltage regulator and sends a duty cycle command back to the voltage regulator to regulate the amount of field current supplied to the generator. The generator has an internal voltage regulator. The generator and voltage regulator are installed as an assembly.
    I'll send wiring diagram tomorrow.

    please rate

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    1 Answer

    2000 Ram Van - is the voltage regulator located in the alternator

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    Service engin soon , Anti lock brake, & Trac control lights came on while driving 55 mph


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    1997 Cadillac Catera: When the AC is on and the cooling fan comes on the charging guage drops to almost the red. voltage at battery drops from 14.6 to 13.2 and shows undercharge on a battery testing meter....

    A charge rate of 13.2 is fine...Likely your battery is getting older and is not charging as well as it used to. You should periodically re-charge the battery using an external charger, as the alternators actual function is to maintain the batteries state of charge, not to re-charge it. Opening the doors, playing the radio with the engine off etc, can and will drain your battery. The alternator will only put a surface charge there and will not actually replace this lost power. I'd begin to worry if charge rate dropped below 12.9.but even then you likely would not have any real problems.

    Jul 16, 2009 | 1997 Cadillac Catera

    1 Answer

    Alternator problem?

    check battery voltage with engine off. should be @ 12.5v
    check with engine running at about 1500 rpms. It should be @ 14 volts. If yes, it is ok. I think you are ok.
    Please rate higly if htis helps

    your system is more sophisticated than Sars can handle.

    here's how it works.

    The charging system consists of a generator which generates current to supply the vehicle electrical system and maintain the battery in a charged condition.
    The generator is driven by the accessory drive belt. For additional information, refer to Section 303-05 . When the engine is started, the generator begins to generate alternating current (AC) which is converted to direct current (DC) internally. The DC current is controlled by the voltage regulator (located on the back of the generator), and then supplied to the battery.
    The charging system voltage is controlled by the powertrain control module (PCM). The generator charges the battery and at the same time it supplies all the electrical loads that are required. The battery is more effectively charged with a higher voltage when the battery is cold and a lower voltage when the battery is warm. The PCM is able to adjust the charging voltage according to battery temperature by using a signal from the intake air temperature (IAT) sensor. This means that the voltage setpoint is calculated by the PCM and communicated to the regulator by a communication link.
    The PCM simultaneously controls and monitors the output of the generator. When the current consumption is high or the battery is discharged the system is able to increase the idle speed.
    To minimize the engine drag when starting the engine, the PCM controls the generator. The generator does not produce any output until the engine has started. The PCM then progressively increases the output of the generator.
    The PCM controls the operation of the charging system warning indicator in the instrument cluster. The PCM is therefore responsible for turning the warning indicator off after the engine is started and illuminating it under fault conditions (when the generator is not generating the correct amount of current with the engine running). The warning indicator will also be illuminated by the PCM at key - on engine off and stall conditions.

    May 10, 2009 | 2006 Ford Focus

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