For 1990-2009 cars
Engine Controls Component Views
Oil Level, ETC, Cruise Control and Generator
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and one destination) into the PCM. The PCM applies ignition voltage to the generator L terminal circuit. A small amount of current flows from this circuit through the generator windings to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.

The PCM expects to detect low voltage on the L terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational. When the PCM detects a fault (circuit shorted to ground, or circuit shorted to a voltage), the battery lamp will illuminate.

### Diagnostic Aids

Important:

• | Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

• | For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Wiring Systems.

A generator fault, such as a shorted output diode, malfunctioning regulator, an open or shorted rotor, or an open sense lead may cause a low battery charge condition. Refer to Charging System Check in Engine Electrical.

### Test Description

The numbers below refer to the step numbers on the Diagnostic Table.

1. This step determines if a fault is present.

2. A poor connection at the generator causes no output.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install a scan tool.
2. Start the engine.
3. Monitor the Generator L terminal parameter using a scan tool.

Does the scan tool display the Generator L terminal as Inactive?

--

Go to DTC P1637 Generator L-Terminal Circuit

Go to Step 3

3 | Measure the voltage at the battery using the DMM J 39200 . Is the battery voltage within the specified range? | 13-15V | Go to Diagnostic Aids | Go to Step 4
4 | Probe the Generator battery feed circuit using the Test Lamp J 35616-200 connected to ground. Refer to Probing Electrical Connectors in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 5 | Go to Charging System Check in Engine Electrical
5 |

1. Disconnect the electrical connector from the generator.
2. Start the engine.
3. Measure the voltage to ground at the generator harness connector terminal B using the DMM J 39200 . Refer to Measuring Voltage in Wiring Systems.

Is the voltage the same or more than the specified value ?

10V

Go to Step 10

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector C2 located on the opposite side of the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
3. Test the continuity from the generator circuit at the PCM harness connector to the B terminal of the generator harness connector using the DMM J 39200 . Refer to Testing for Continuity in Wiring Systems.

Does the DMM indicate continuity?

--

Go to Step 8

Go to Step 7

7 | Repair the open/high resistance in the generator circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | System OK | --
8 |

1. Inspect the terminal contact tension at the PCM harness connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a poor connection, repair the connection as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Step 9

9 | Important:: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | System OK | --
10 |

1. Inspect the terminal contact tension at the generator electrical connector. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.
2. If you find a poor connection, repair the connection as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

System OK

Go to Step 11

11 | Replace the generator. Refer to Generator Replacement in Engine Electrical. Is the action complete? | -- | System OK | --