TSB C: EXPERTEC TSB (56-81-02)

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Publication date: 1995-03-30 Reference number: 56-81-02 EXPERTEC TSB EXPERTEC TSB TECHNICAL SERVICE BULLETIN Reference Number(s): 56-81-02, Date of Issue:  03/30/95 SMU - SECTION 8A - 30 - START AND CHARGE Model(s): 1994 Chevrolet and GMC Truck M/L Models Date: 03/30/1995 Bulletin Number Chevrolet 56-81-02 DESCRIPTION Subject: Section 8A-30 - Start and Charge This bulletin updates pages 8A-30-1, 8A-30-5, 8A-30-6, and 8A-30-7 in Section 8A-30 of the 1994 M/L Driveability, Emissions and Electrical Diagnosis Manual. START AND CHARGE, STARTER, CIRCUIT OPERATION When the Ignition Switch is moved to the START position, battery voltage is supplied to the Starter Solenoid through the PPL (6) wire. Both solenoid windings are energized. The circuit through the Pull-In Winding is completed to ground through the Starter Motor. The windings work together magnetically to pull in and hold in the Plunger. The Plunger moves the Shift Lever. This action causes the Drive Assembly to rotate as it engages the Flywheel ring gear on the engine. At the same time, the Plunger also closes the solenoid switch contacts in the Starter Solenoid. Full battery voltage is then applied directly to the Starter Motor and it cranks the Engine. As soon as the Solenoid Switchcontacts close, voltage is no longer applied to the Pull-In Winding, since battery voltage is applied to both ends of the windings. The Hold-In Winding remains energized and its magnetic field is strong enough to hold the Plunger, Shift Lever, and Drive Assembly Solenoid Switch contacts in place to continue cranking the engine. When the Ignition Switch is released from the START position, battery voltage is removed from the PPL(6) wire and the junction of the two windings. Voltage is applied through the motor contacts to both windings to ground at the end of the Hold-In Winding. However, the voltage supplied to the Pull-In Winding is now opposing the voltage supplied when the winding was first energized. The magnetic fields of the Pull-In and Hold-In Windings now oppose one another. This action of the windings, with the help of the Return Spring, causes the Starter Drive Assembly to disengage and the Solenoid Switch contacts to open simultaneously. As soon as the contacts open, the starter circuit is turned off. CHARGING The Generator provides voltage to operate the vehicle's electrical system and to charge its Battery. A magnetic field is created when current flows through the Rotor. This field rotates as the Rotor is driven by the engine, creating an AC voltage in the stator windings. The AC voltage is converted to DC by the rectifier bridge and is supplied to the electrical system at the Battery terminal. The Generator's Regulator uses digital techniques to supply the Rotor current and thereby control the output voltage. The Rotor current is proportional to the width of the electrical pulses supplied by the Regulator. When the Ignition Switch is placed in RUN, narrow width pulses are supplied to the Rotor, creating a weak magnetic field. When the Engine is started, the Regulator senses Generator rotation by detecting AC voltage at the Stator through an internal wire. Once the Engine is running, the Regulator varies the field current by controlling the pulse width. This regulates the Generator output voltage for proper battery charging and electrical system operation. A signal to the 'I' or 'L' terminal must be present to turn the generator on. The 'I' circuit can be connected directly to battery voltage, whereas the 'L' circuit must have a resistance of 35 to 560 ohms. When a fault is detected, under charge, over charge, or the generator is not turning, the lamp driver circuit in the regulator grounds the 'L' terminal providing a ground path for the lamp indicator. With little or no resistance in the circuit, the IC's current capacity is exceeded, and the regulator can be damaged. Typical lamp resistance is 13.5 ohms cold, 140 ohms when lit. A resistor is placed parallel to the lamp to provide turn-on should the lamp not properly function. CAUTION: NEVER APPLY 12 VOLTS TO THE GENERATOR 'L' CIRCUIT! TROUBLESHOOTING HINTS: Visually inspect the hydrometer (built into Battery). Green eye - Battery is charged. Dark eye - Charge and load test Battery, refer to Section 6. If Battery passes load test, refer to System Diagnosis, Section 8A-30. Clear or light yellow eye - Battery electrolyte is low. Replace Battery. Check for proper installation of aftermarket electronic equipment which may affect the integrity of other systems. CAUTION: The following tests are designed for engines and batteries at normal operating temperatures and assumes that there are no engine symptoms which would cause a no-start symptom. The Battery must be in a charged state before doing diagnosis. To use the tests under other conditions could result in misdiagnosis. STARTER Check that Starter Solenoid terminals "S" and "B" and Battery connections are clean and tight. Check that G100 and G102 are clean and tight. Check for a broken (or partially broken) wire inside of the insulation which could cause system failure but prove "GOOD" in a continuity/voltage check. Use Test Light J 34142 whenever possible. Test lights require more current than a high impedance DVM and arc more useful for detecting abnormally high resistive circuits. Some test lights have high impedances and will not be as useful in detecting resistive circuits. CHARGING SYSTEM Check Gages Fuse for open. Check that the Generator connector and Generator "BAT" terminal are both clean and tight. Check that the Battery connections are clean and tight. Check Generator belt. Check that Fusible Link is undamaged. If Fusible Link is open, check for a short to Ground Circuit 2 and Generator. BULLETIN ILLUSTRATION LIST Fig 1: GRAPHIC Courtesy of GENERAL MOTORS CORP. Fig 2: GRAPHIC Courtesy of GENERAL MOTORS CORP. Fig 3: GRAPHIC Courtesy of GENERAL MOTORS CORP.