P2503
P2503-CHARGING SYSTEM OUTPUT LOW
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 RPM is high enough to assure sufficient Generator current output to satisfy the electrical loads.
- Set Condition:
The battery sensed voltage is less than the target charging voltage, during engine operation, for a calibrated amount of time. One Trip Fault. Generator light will illuminate. If the vehicle is equipped with the stop/start feature, the system will be disabled when this DTC is active.
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Pre-Diagnostic Troubleshooting Procedure.
Diagnostic Test
1. ACTIVE DTC
NOTE: Inspect the vehicle for aftermarket accessories that may exceed the Generator System output.
NOTE: The battery must be fully charged.
NOTE: The Generator belt tension and condition must be checked before continuing.
1. Ignition on, engine not running.
2. With a scan tool, select View DTCs.
3. Read and record the related Freeze Frame data.
4. With a scan tool, erase DTCs.
5. Start the engine.
6. Allow the idle to stabilize.
7. Ignition on, engine not running.
8. Using the scan tool, read the active DTCs.
Is the DTC Active at this time?
Yes
- Go To 2
No
- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.
2. CHECK THE (A804) GENERATOR SENSE CIRCUIT OUTPUT
1. Will
2. Start the engine.
3. Measure the voltage at the Generator B+ Output Terminal.
4. Back probe and measure the voltage of the (A804) Generator Sense circuit at the Generator Field harness connector.
NOTE: The voltage reading at the (A804) Generator Sense circuit should be within 0.25 volts of the voltage reading at the Generator B+ Output Terminal.
Are the voltage readings within 0.25 volts?
Yes
- Go To 3
No
- Verify that there is good pin to terminal contact in the Generator connector. If OK, replace the Generator. Service and Repair.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
3. CHECK THE (A804) GENERATOR SENSE CIRCUIT FOR HIGH RESISTANCE
1. Turn the ignition off.
2. Using a voltmeter, probe the (A804) Generator Sense circuit at the Generator Field harness connector with one lead.
3. Back probe the (A804) Generator Sense circuit at the PCM C2 harness connector with the other lead.
4. Start the engine.
5. Measure the voltage drop on the (A804) Generator Sense circuit.
Is the voltage above 0.25 volts?
Yes
- Repair the excessive resistance in the (A804) Generator Sense circuit between the Generator and PCM.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Go To 4
4. 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 the Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.
Were there any problems found?
Yes
- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.
No
- Replace and program the Powertrain Control Module (PCM). Powertrain Control Module - Removal.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.