P2503
P2503-CHARGING SYSTEM OUTPUT LOW
For a complete wiring diagram refer to: Electrical Diagrams
When Monitored
The engine running. The engine speed greater than 1157 RPM.
Set Condition
The battery sensed voltage is 1 volt below the charging goal for 13.47 seconds. The PCM senses the battery voltage turns off the field driver and senses the battery voltage again. If the voltages are the same, the code is set. One Trip Fault. Three good trips to turn off the MIL.
Possible Causes
- EXCESSIVE RESISTANCE IN THE BATTERY POSITIVE CIRCUIT
- EXCESSIVE RESISTANCE IN THE CASE GROUND
- (K20) GEN FIELD CONTROL CIRCUIT SHORTED TO VOLTAGE
- (K20) GEN FIELD CONTROL CIRCUIT OPEN
- (K20) GEN FIELD CONTROL CIRCUIT SHORTED TO GROUND
- (Z904) GEN GROUND CIRCUIT OPEN GENERATOR
- PCM
Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding.
Diagnostic Test
1. ACTIVE DTC
NOTE: Inspect the vehicle for aftermarket accessories that may exceed the Generator System output.
Ignition on, engine not running.
NOTE: The battery must be fully charged.
NOTE: The Generator belt tension and condition must be checked before continuing. With a scan tool, read DTCs.
With a scan tool, erase DTCs.
Start the engine.
Allow the idle to stabilize.
With the scan tool, read DTCs.
Is the DTC active at this time?
Yes >> Go To 2
No >> Refer to the INTERMITTENT CONDITION Diagnostic Procedure.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
2. FUSED 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 can result in personal injury or death.
Ignition on, engine not running.
NOTE: Make sure all wires are clear of the engine's moving parts.
Measure the voltage between the Generator B+ Output Terminal and the Battery+ Post.
Start the engine.
Is the voltage above 0.4 of a volt?
Yes >> Repair the excessive resistance in the battery positive circuit between the Generator and Battery.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
No >> Go To 3
3. EXCESSIVE RESISTANCE IN THE CASE GROUND
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 can result in personal injury or death.
Start the engine.
Warm the engine to operating temperature.
NOTE: Make sure all wires are clear of the engine's moving parts.
Measure the voltage between the Generator Case and Battery ground post.
Is the voltage above 0.1 of a volt?
Yes >> Repair the excessive resistance in the Generator Case Ground.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
No >> Go To 4
4. GENERATOR OPERATION
Turn the ignition off.
Disconnect the Generator Field harness connector.
Using a 12-volt test light, jump across the Generator Field harness connector.
Ignition on, engine not running. With a scan tool, actuate the Generator Field Driver.
Does the test light illuminate brightly and flash on and off?
Yes >> Replace the Generator.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
No >> Go To 5
5. (K20) GEN FIELD CONTROL CIRCUIT SHORTED TO BATTERY VOLTAGE
Turn the ignition off.
Disconnect the PCM harness connectors.
Ignition on, engine not running.
Measure the voltage on the (K20) Gen Field Control circuit in the Generator Field harness connector.
Is the voltage above 1.0 volt?
Yes >> Repair the short to battery voltage in the (K20) Gen Field Control circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
No >> Go To 6
6. (K20) FIELD CONTROL CIRCUIT OPEN
Turn the ignition off.
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 Miller Special Tool #8815 to perform diagnosis.
Measure the resistance of the (K20) Gen Field Control circuit from the Generator Field harness connector to the appropriate terminal of special tool #8815.
Is the resistance below 5.0 ohms?
Yes >> Go To 7
No >> Repair the open in the (K20) Gen Field Control circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
7. (K20) GEN FIELD CONTROL CIRCUIT SHORTED TO GROUND
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 POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
No >> Go To 8
8. (Z904) GROUND CIRCUIT OPEN
Using a 12-volt test light connected to battery voltage, probe the (Z904) Ground circuit in the Generator Field harness connector.
Does the test light illuminate brightly?
Yes >> Go To 9
No >> Repair the open in the (Z904) Generator Ground circuit.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
9. PCM
NOTE: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.
Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes >> Repair as necessary
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3
No >> Replace and program the Powertrain Control Module per Service Information.
Perform POWERTRAIN VERIFICATION TEST. Powertrain Verification Test - Ver 3