P063A-GENERATOR VOLTAGE SENSE CIRCUIT
For a complete wiring diagram, refer to the Wiring Information.
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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.
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When Monitored:
The engine running. The engine speed greater than 1157 RPM.
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Set Condition:
The Powertrain Control Module (PCM) recognizes the alternator output voltage is less than the Battery feed circuit voltage. One trip failure. The Generator light will illuminate. The fault will be checked again on the next key cycle.
Possible Causes |
|---|
| EXCESSIVE RESISTANCE IN THE (A804) GENERATOR SENSE CIRCUIT |
| (A804) GENERATOR SENSE CIRCUIT SHORTED TO GROUND |
| GENERATOR |
| POWERTRAIN CONTROL MODULE (PCM) |
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
| 1. | Start the engine and allow it to reach normal operating temperature. |
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.
WARNING:
| 2. | With the scan tool, select View DTCs. |
Is the DTC Active at this time
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
2. CHECK THE (A804) GEN SENSE CIRCUIT FOR A SHORT TO VOLTAGE
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| 1. | Turn the ignition off. |
| 2. | Disconnect the Generator harness connector. |
| 3. | Disconnect the Powertrain Control Module (PCM) C2 harness connector. |
| 4. | Turn the ignition on. |
| 5. | Measure the voltage on the (A804) Gen Sense circuit at the Generator harness connector. |
Is there any voltage present?
Yes
- Repair the (A804) Gen Sense circuit for a short to voltage.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
No
-
Go To 3
3. CHECK THE (A804) GEN SENSE CIRCUIT FOR A SHORT TO GROUND
 |
| 1. | Turn the ignition off. |
| 2. | Measure the resistance between ground and the (A804) Gen Sense circuit at the Generator harness connector. |
Is the resistance above 10k Ohms?
Yes
- Go To 4
No
- Repair the (A804) Gen Sense circuit for a short to ground.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
4. CHECK THE (A804) GEN SENSE CIRCUIT FOR AN OPEN/HIGH RESISTANCE
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 GPEC Diagnostic Adaptor to perform
the diagnosis.
CAUTION:
| 1. | Connect the Adapter, GPEC Diagnostic 10436 . |
| 2. | Measure the resistance of the (A804) Gen Sense circuit between the Generator harness connector and the GPEC Adaptor. |
Is the resistance below 5.0 Ohms?
Yes
- Go To 5
No
- Repair the (A804) Gen Sense circuit for an open or high resistance.
-
Perform the POWERTRAIN
VERIFICATION TEST. (Refer to
28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM)
- Standard
Procedure).
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.
WARNING:
| 1. | Connect the Generator harness connector. |
| 2. | Connect the GPEC Adapter to the Powertrain Control Module (PCM) C2 connector. |
| 3. | Turn the ignition on. |
| 4. | Measure the voltage of the (K20) Gen Field Control circuit at the GPEC Adapter. |
| 5. | Start the engine. |
| 6. | With the scan tool, perform the Generator Full Field test. |
| 7. | Monitor the voltage of the (K20) Gen Field Control circuit with the Generator Full Field test actuated. |
| NOTE: | The voltage should increase more than 1 Volt. |
Does the voltage increase by at least 1 Volt with the Generator Full Field Test on?
Yes
- Go To 6
No
- Replace the Generator in accordance with the Service Information. (Refer to 08 - Electrical/8F - Engine Systems/Charging/GENERATOR - Removal) .
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
6. 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. |
| 4. | Perform any Technical Service Bulletins that may apply. |
Were any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).
No
- Replace and program the Powertrain Control Module (PCM) in accordance with the Service Information. (Refer to 08 - Electrical/8E - Electronic Control Modules/MODULE, Powertrain Control - Removal) .
- Perform the POWERTRAIN VERIFICATION TEST. (Refer to 28 - DTC-Based Diagnostics/MODULE, Powertrain Control (PCM) - Standard Procedure).