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Discussion Starter #1
I've yet to hear anyone else mention it, but my car has a rather unnerving electrical habbit. With no rhyme or reason I'm noticing a signifigant speed drop in the hvac fan during stops and on occasional shifts. Tonight on the way home from work noticed that the lights are dimming at the same time. (it would be very nice to have a volt guage in the car) Has anyone else experienced this or do I have a special car?
 

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I haven't had that problem. Your right you do need a volt gage on the car. Set one up because it sound like your not getting full charge at idle.
 

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darkitec said:
I've yet to hear anyone else mention it, but my car has a rather unnerving electrical habbit. With no rhyme or reason I'm noticing a signifigant speed drop in the hvac fan during stops and on occasional shifts. Tonight on the way home from work noticed that the lights are dimming at the same time. (it would be very nice to have a volt guage in the car) Has anyone else experienced this or do I have a special car?
Sounds like perhaps you blew a diode pack - or at least one. This allows the alternator to still charge the system, but the dead diode no longer keeps the alternating current the alternator produces going in the right direction (DC flow). Since the output of the alternator is lower at an idle, it appears that things aren't charging. Think of it as pointing a hose into a small creek and pushing some of the water back upstream. the bigger the creek, the more correct flow you get and the hose becomes insignificant. Slow down the flow of the creek and the hose becomes a more major player.
In any event, you have a charging system that is not playing nice. Better have your friendly neighborhood dealer see to it. ;)
 

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Discussion Starter #4
I guess I should clarify. The Drop is breif, 1/4 second or so. (I had an old car that would die suddenly without warning) It has that sort of feeling to it.
 

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darkitec said:
I guess I should clarify. The Drop is breif, 1/4 second or so. (I had an old car that would die suddenly without warning) It has that sort of feeling to it.
I wouldn't worry about that too much. I had an 96 ImpalaSS that did the identical thing, and several of my other cars have done similar things. It may be the difference between older vehicles and newer ones in that the newer ones try to keep a constant voltage output regardless of the engine speed. Older cars were happy with something close to the ideal voltage. Constant voltage is easier to deal with when using computers. When the engine speed comes down from where it it would be capable of producing much more than what is needed (or desired), the circuit that controls the output has to adjust for the reduced flow and this momentary dip is that re-adjustment. Think of it as the forces needed to hold back a 100 amp capability suddenly only need to hold back and maintain only about 35 to 40 amps. The input to the fields has to be adjusted to maintain the base voltage. You're hearing that adjustment. No biggy.
If it stays down, that's a problem, but I wouldn't worry about what yours is doing. Motor on and keep smiling! :)
 

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Yes, it has a car seat
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My '95 Saturn would dim the lights and brighten them up when you hit the gas. It was much more noticible when the battery started going dead though.
Dan
 

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Do you notice a momentary engine power drop when the fan speed slows down? Some cars exhibit this more than others when the A/C compressor kicks in. It will kick in when you are using the defrost setting, whether you select the A/C button or not. When it kicks in, one of the engine cooling fans starts also, I think. This initial heavier current load will dim the lights a bit sometimes.

Just a chance this might be what you're noticing. Hope it's that simple and you don't have a worse problem.
 

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Knight Errant
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Electrical

Mine has no such problem, A/C on or not. It is a 140 amp alternator and should be able to handle the load. I suspect some BCM module involvement as has been said for some of the other electrical 'spooks' the car seems to have, either the harness rubbing against something back there or a grounding issue as has been said of the A4's elsewhere on this Forum by many members. That is where I'd start looking anyway.
 

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Discussion Starter #9
Woah there's a new one. Sitting at the stop light this morning and the spedo. snaked it's way up to 200 mph. Stayed there untill I started moving. Movement of all guages a bit jerky, repeated a couple more times. Finally broke down and did a hard reboot. Ie turn off ignition and restart car. Curious to see if it's going to happen again on the drive home.
 

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darkitec said:
I've yet to hear anyone else mention it, but my car has a rather unnerving electrical habbit. With no rhyme or reason I'm noticing a signifigant speed drop in the hvac fan during stops and on occasional shifts. Tonight on the way home from work noticed that the lights are dimming at the same time. (it would be very nice to have a volt guage in the car) Has anyone else experienced this or do I have a special car?
This may help you
DTC P0562
Circuit Description
The powertrain control module (PCM) continuously monitors the system voltage. The system voltage information is taken from the ignition feed circuit to the PCM. Voltages below 8.0 volts or above 17.1 volts cause improper system operation and/or component damage. The PCM operates in a default mode if a PCM voltage DTC sets. If the system voltage is low, the PCM raises the idle speed to increase the generator output. The PCM disables most outputs to protect the hardware if the system voltage is high. Tech 2 will not display data if system voltage is outside this range. Use a DMM to monitor the system voltage to check to see if the fault is currently present. DTC P0562 is a type 'C' DTC.

Conditions for Running the DTC
The engine is running longer than ten seconds
Engine speed is above 1,500 RPM.
Vehicle speed is above 8 km/h (5 mph).
Conditions for Setting the DTC
The PCM detects a system voltage below 8.5 volts for 10 seconds.

Action Taken When the DTC Sets
The PCM stores the DTC information into memory when the diagnostic runs and fails.
The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.
The PCM will not illuminate the malfunction indicator lamp (MIL).
The multi function display (MFD) in the Instrument cluster will display a message at key-on and key-off.
The transmission will default to third gear.
The PCM will inhibit torque converter clutch (TCC) operation.
Conditions for Clearing the DTC
The DTC clears when the diagnostic runs and passes.
The history DTC will clear after 40 consecutive warm-up cycles have occurred without a malfunction.
The DTC can be cleared by using a scan tool.
Diagnostic Aids
An extremely low voltage (below 7.5 volts) may cause the loss of serial data. An open ignition feed circuit causes a No Start and the MIL will not illuminate. A low system voltage may cause other DTCs to set.
Using the Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Failure Records data can aid in determining the distance travelled since the DTC reported a pass and/or fail. Operate the vehicle within the same Failure Records conditions (RPM, load, vehicle speed, temperature, etc.) that you observed. This will isolate when the DTC failed.
For an intermittent, refer to Testing for Intermittent and Poor Connections in Body and Accessories-Wiring Systems.
Step
Action
Value(s)
Yes
No

Schematic Reference: Engine Controls Schematics in Engine Controls - 5.7L

Connector End View Reference: Engine Controls Connector End Views in Engine Controls - 5.7L

1
Did you perform the Engine Electrical Diagnostic System Check?
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Go to Step 2
Go to Diagnostic System Check - Engine Electrical

2
Turn ON the ignition, with the engine OFF.
With a scan tool, observe the Ignition 1 Signal parameter in the PCM data list .
Does the scan tool indicate that the Ignition 1 Signal parameter is greater than the specified value?
8.0 V
Go to Step 7
Go to Step 3

3
Measure the voltage at the battery and compare it with the Ignition 1 Signal parameter in the PCM data list.

Are the battery voltage and PCM Ignition 1 readings different by more than the value specified?
0.5 V
Go to Step 4
Go to Charging System Test

4
Test the battery positive voltage circuit of the PCM for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
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Go to Step 8
Go to Step 5

5
Test the battery ground circuit of the PCM for a high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
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Go to Step 8
Go to Step 6

6
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?
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Go to Step 8
Go to Step 7

7

Important
The replacement PCM must be programmed.


Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement in Engine Controls - 5.7L.

Did you complete the replacement?
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Go to Step 8
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8
Review and record the scan tool Fail Records data.
Use the scan tool in order to clear the DTC.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Using the scan tool, observe the Specific DTC Information for DTC P0562 until the test runs.
Does the scan tool indicate that DTC P0562 failed this ignition?
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Go to Step 3
System OK



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Charging System Description and Operation
Generator
The GTO is fitted with a Mitsubishi 140-amp generator. This generator is mounted on the lower , left --hand side of the engine. It has an internally mounted regulator; a single lower mounting lug and no external cooling fans.

The generator is 3 phase, incorporating a rotor with 6 pole pairs and 2 internal cooling fans; one on the drive end and one on the slip-ring end. The rotor is supported by ball bearing races in both the drive and slip-ring end housings. The stator surrounds the rotor and has a 3-phase star connected output winding on a ring shaped lamination pack.

The output of the stator winding is rectified by 8 diodes within the slip-rind end housing, Excitation current is supplied to the rotor field coil via the voltage regulator, the brushes and slip-rings. The electronic voltage regulator requires no adjustment in service.

The generator has 4 external connections:

B+ lead to the battery positive terminal
L lead to the generator warning lamp (max. 2 watts)
S lead for battery voltage sensing
ground connection (via the installation bolts)
Circuit Description
With the ignition switched on , current is supplied via the warning lamp to the L terminal of the regulator. This allows current to flow (within the regulator) from the generator B+ to the brushes and rotor winding.

The current in the rotor winding creates magnetic fields between adjacent rotor poles. As the rotor spins, the stator winding cut through this field at right angles and induce voltage. As the speed increases, this induced voltage increases. Current then flows through the three-phase diode bridge in the rectifier to convert the AC voltage to DC. This is supplied to the B+ output ant hen to the battery.

The regulator S terminal monitors the system voltage. When this voltage reaches approximately 14.2 volts, the regulator breaks the circuit through the rotor winding, causing the generator output voltage to drop. When the regulator S terminal senses a voltage below a preset value, the regulator completes the circuit and voltage to the battery again increases. This cycle repeats very rapidly.

If the warning lamp fails, the generator self excites by using current from the phase connection until the voltage builds up to the regulating level

Current does not flow through the rotor winding when the engine is cranking.

Standby Mode
With the ignition on and the engine at rest, the regulator defaults to active standby mode. This limits the current through the rotor by switching ON and OFF at 50 percent duty cycle with a frequency of approximately 4 kHz. This is audible at times.

Backup mode
The regulator compares voltage at the B+ terminal with voltage sensed at the S terminal. The regulator defaults to backup mode if the difference exceeds a preset value. Backup mode limits the output voltage to a safe level approximately 1-3 volts above the normal setting.

Warning Lamp Conditions
The regulator illuminate the warning lamp when it detects a fault condition in the generator or the external circuits. The warning lamp remains illuminated until all faults are repaired.

Fault conditions include:

Open circuit in the regulator battery sensing wire S terminal
Open circuit or excessive voltage drop in the B+ cable
Open circuit in the generator phase connection
Overcharge of the battery
Short circuit in the regulator output stage
Open circuit in the rotor winding
Poor contact in a wiring harness connector
Poor contact between the rectifier and the regulator
High resistance in the fusible link assembly
Poor contact between the battery terminals and cables
 
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