Powertrain Control Module (PCM) - NGC
P0562-BATTERY VOLTAGE LOW
Special Tools:
For a complete wiring diagram, refer to the Wiring Information.
Theory of operation
The Powertrain Control module (PCM) 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 PCM uses the PWM signal input to determine the generator load on the engine. This allows the PCM to adjust the idle speed to compensate for high electrical loads. The PCM monitors the status of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5-95 percent.
- When Monitored:
The engine running. The engine speed greater than 1000 RPM.
- Set Condition:
Battery voltage is below 6 Volts. Two Trip Fault.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
1. ACTIVE DTC
NOTE: Make sure the Battery is in good condition. Test the Battery before continuing.
NOTE: Inspect the vehicle for after market accessories that may exceed the Generator System output.
NOTE: Make sure the generator drive belt is in good operating condition.
NOTE: Inspect the fuses in the TIPM. If an open fuse is found, use the wire diagram/schematic as a guide, inspect the wiring and connectors for damage.
1. Start the engine.
2. Allow the engine to reach normal operating temperature.
3. With the scan tool, select View DTCs.
NOTE: It may be necessary to drive the vehicle to meet the conditions to set this DTC, try to repeat the conditions in which the fault originally set by reviewing the Freeze Frame data.
Is the DTC Active or Pending at this time?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test
2. (A11) B+ CIRCUIT HIGH RESISTANCE
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
NOTE: Make sure all wires are clear of the engine's moving parts.
1. Perform a voltage drop test between the (A11) B+ Terminal at the Generator and the Battery + Post.
2. Start the engine.
Is the voltage above 0.4 of a Volt?
Yes
- Repair the excessive resistance in the (A11) B+ circuit between the Generator and Battery.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 3
3. GENERATOR CASE GROUND HIGH RESISTANCE
WARNING: When the engine is operating, do not stand in direct line with the fan. Do not put your hands near the pulleys, belts or fan. Do not wear loose clothing. Failure to follow these instructions may result in possible serious or fatal injury.
1. Ignition on, engine not running.
2. Start the engine.
3. Allow the engine to reach normal operating temperature.
4. Perform a voltage drop test between the Generator case and Battery ground post.
Is the voltage above 0.1 of a Volt?
Yes
- Repair excessive resistance in the Generator Ground between the Generator Case and Battery ground side.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 4
4. GENERATOR OPERATION
1. Turn the ignition off.
2. Disconnect the Generator Field harness connector.
3. Using a 12-volt test light connected to ground, probe the (K20) Generator Field Control circuit in the Generator Field harness connector.
NOTE: Make sure the test light is probing the circuit before actuating the Test or a DTC may set and not allow the actuation.
4. With the scan tool, actuate the Generator Field Driver.
NOTE: The test light should be illuminated and bright proportional to the maximum duty cycle allowed by the scan tool. For example, if the scan tool allows 100% actuation, the brightness should be as bright as a direct connection to the battery. If the scan tool allows a maximum 25% actuation, the brightness should be 25% as bright as a direct connection to the battery.
Does the test light illuminate accordingly during the actuation?
Yes
- Verify that there is good pin to terminal contact in the Generator and Powertrain Control Module connectors. Replace the Generator if no issues were found with the connectors. Generator - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 5
5. (K20) GENERATOR FIELD CONTROL CIRCUIT OPEN
1. Turn the ignition off.
2. Disconnect the C2 PCM harness connector.
CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install the PCM Pinout Box (8815A) to perform diagnosis.
3. Measure the resistance of the (K20) Gen Field Control circuit from the Generator harness connector to the appropriate terminal of the PCM Pinout Box.
Is the resistance below 5.0 Ohms?
Yes
- Go To 6
No
- Repair the open in the (K20) Gen Field Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
6. (K20) GENERATOR FIELD CONTROL CIRCUIT SHORTED TO GROUND
1. Measure the resistance between ground and the (K20) Gen Field Control circuit in the Generator Field harness connector.
Is the resistance below 100 Ohms?
Yes
- Repair the short to ground in the (K20) Gen Field Control circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 7
7. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Generator and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the Generator and Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.
Were there any issues?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Replace and program the Powertrain Control Module. PCM/ECM/TCM Reprogramming
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.