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Tahoe / Yukon Service Manual

Charging System Test

Diagnostic Instructions Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. Review Strategy Based Diagnosis for an overview of the diagnostic approach. Diagnostic Procedure Instructions provides an overview of each diagnostic category. Diagnostic Fault Information

Circuit Short to Ground Open/High Resistance Short to Voltage Signal Performanc
B+ – P0621 — —
Control – L Terminal P0621 — P0621 —
Signal – F Terminal P0622 P0622 P0622 P0622

Circuit/System Description The K20 Engine Control Module (ECM) uses the G13 Generator turn ON control circuit, or L- terminal circuit, to control the load of the Generator on the engine. A high side driver in the ECM applies a duty cycled voltage to the voltage regulator. The duty cycle controls the voltage regulator to turn the field circuit ON and OFF. The ECM monitors the state of the generator turn ON control circuit. The ECM should detect low voltage on the generator turn on control circuit when the ignition is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the ECM should detect high voltage when the duty cycle voltage is commanded high and a low voltage when the duty cycle voltage is commanded low on the generator turn on control circuit. The ECM uses the generator field duty cycle signal circuit, or F-terminal circuit, to monitor the duty cycle of the Generator. The Generator field duty cycle signal circuit connects to high side of the field windings in the generator. A Pulse Width Modulated (PWM) high side driver in the voltage regulator turns the field windings on and off. The ECM uses the PWM signal input to determine the generator load on the engine. This allows the ECM to adjust the idle speed to compensate for high electrical loads. The ECM monitors the status of the generator field duty cycle signal circuit. When the ignition is ON and the engine is off, the ECM should detect a duty cycle near 0%. When the engine is running, the duty cycle should be between 5–99%. Diagnostic Aids Verify the following component is properly installed: Drive Belt If necessary, perform the following steps: Battery Electrical Drain/Parasitic Load Test To save fuel, the generator does not charge when the following parameter shows the given state: Fuel Economy Mode is Active When an accessory is switched on, the response of the charge current (respectively the battery voltage) is not instantaneous. The generator slowly ramps up the charge current. If the battery is fully charged, the charge current may not increase at all. This behavior can make it difficult to measure the charge current or a change in battery voltage. Voltmeter gauge fluctuation is not an indicator of a charging system malfunction. Depending on the charging system mode and system loading, battery voltage can fluctuate between 12.0 V to 15.8 V. Refer to Description and Operation. A charging system malfunction is indicated by illuminating the charge indicator, and/or a Driver Information Center Message: BATTERY NOT CHARGING SERVICE CHARGING SYSTEM or SERVICE BATTERY CHARGING SYSTEM . The generator will default to a voltage output of 13.8 V if the G13 Generator X1 connector is disconnected. Reference Information Schematic Reference Starting and Charging Schematics Connector End View Reference Master Electrical Component List Description and Operation Charging System Description and Operation Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs Circuit/System Verification

  1. Ignition » On / Vehicle » In Service Mode
  2. Verify the charge indicator is On while the instrument cluster performs the bulb check. Approximately 4 seconds. ⇒ If the indicator is Off during the bulb check. Approximately 4 seconds Replace P16 Instrument Cluster ⇓ If the indicator is On during the bulb check. Approximately 4 seconds
  3. Verify there are no DTCs set related to the following system/component: B18 Battery Current Sensor (If applicable) B110 Battery Sensor Module (If applicable) G13 Generator Energy Management Stop/Start System (KL9) ⇒ If any DTC is set Refer to: Diagnostic Trouble Code (DTC) List - Vehicle ⇓ If no DTC is set
  4. Increase the engine speed slowly to 2500 RPM. All accessories OFF.
  5. Verify the scan tool Battery Voltage parameter is between 12.0 –15.8 V ⇒ If not between 12.0 – 15.8 V Refer to Circuit System Testing ⇓ If between 12.0 – 15.8 V
  6. Turn the following components ON: Headlamps Rear Defogger Blower Motor at maximum speed
  7. Increase the engine speed slowly to 2500 RPM. Verify the scan tool Battery Voltage parameter is between 12.6 - 15.8 V. ⇒ If not between 12.6 – 15.8 V Refer to Circuit System Testing ⇓ If between 12.6 – 15.8 V
  8. Verify the charge indicator on the instrument cluster is Off and the Driver Information Center (DIC) does not display any charging system error message. ⇒ If the indicator is On Refer to Circuit System Testing ⇓ If the indicator is Off
  9. All OK. Circuit/System Testing
  1. Verify a test lamp illuminates between the G13 Generator B+ circuit terminal A X2 or 1 X2 and ground. ⇒ If the test lamp does not illuminate and the circuit fuse is good 1.1. Remove the test lamp and disconnect the B+ cable at the G13 Generator. 1.2. Test for less than 2 Ω in the B+ circuit end to end. ⇒ If 2 Ω or greater, repair the open/high resistance in the circuit. ⇒ If less than 2 Ω, verify the fuse is not open and there is voltage at the fuse. ⇒ If the test lamp does not illuminate and the circuit fuse is open 1.1. Remove the test lamp, disconnect the battery negative cable, and disconnect the G13  Generator B+ cable. 1.2. Test for infinite resistance between the B+ circuit and ground. ⇒ If less than infinite resistance, repair the short to ground on the circuit. ⇒ If infinite resistance, test or replace the G13 Generator. ⇓ If the test lamp illuminates
  2. Disconnect the X1 harness connector at the G13 Generator, engine running.
  3. Test for 13.4 V to 14 V between the engine block and B+ circuit at G13 Generator. ⇒ If not between 13.4 and 14 V, Test or replace the G13 Generator. ⇓ If between 13.4 and 14 V
  4. Verify the scan tool Engine Control Module Generator F–Terminal Signal parameter is less than 5%. ⇒ If 5% or greater 4.1. Ignition OFF, disconnect the X3 harness connector at the K20 Engine Control Module, ignition ON. 4.2. Test for less than 1 V between the G13 Generator signal circuit terminal 2 X1 and ground. ⇒ If 1 V or greater, repair the short to voltage on the circuit. ⇒ If less than 1 V, replace the K20 Engine Control Module. ⇓ If less than 5%
  5. Install a 3 A fused jumper wire between the signal circuit terminal 2 X1 and B+, engine running.
  6. Verify the scan tool Engine Control Module Generator F–Terminal Signal parameter is greater than 95%. ⇒ If 95% or less 6.1. Ignition OFF, remove the jumper wire, disconnect the X3 harness connector at the K20  Engine Control Module. 6.2. Test for infinite resistance between the signal circuit and ground. ⇒ If less than infinite resistance, repair the short to ground on the circuit. ⇓ If infinite resistance 6.3. Test for less than 2 Ω in the signal circuit end to end. ⇒ If 2 Ω or greater, repair the open/high resistance in the circuit ⇒ If less than 2 Ω, replace the K20 Engine Control Module. ⇓ If greater than 95%
  7. Remove jumper wire. X1 disconnected at G13 Generator, engine running.
  8. Test for 1 V or greater between the control circuit terminal 1 X1 and ground. ⇒ If less than 1 V 8.1. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module. 8.2. Test for infinite resistance between the control circuit and ground. ⇒ If less than infinite resistance, repair the short to ground on the circuit. ⇓ If infinite resistance 8.3. Test for less than 2 Ω in the control circuit end to end. ⇒ If greater than 2 Ω, repair the open/high resistance in the circuit. ⇒ If less than 2 Ω, replace the K20 Engine Control Module. ⇓ If 1 V or greater
  9. Ignition OFF, disconnect the harness connectors at the K20 Engine Control Module, Ignition ON
  10. Test for less than 1 V between the G13 Generator control circuit terminal 1 X1 and ground. ⇒ If greater than 1 V Repair the short to voltage on the circuit. ⇓ If 1 V or less
  11. Test or replace the G13 Generator. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair. Control Module References Control Module replacement, programming and setup. Generator Replacement