For 1990-2009 cars

### Circuit Description

The PCM uses the generator turn on signal circuit to control the load of the generator on the engine. A high side driver in the PCM applies a voltage to the voltage regulator. This signals the voltage regulator to turn the field circuit ON and OFF. When the PCM turns ON the high side driver, the voltage regulator turns ON the field circuit. When the PCM turns OFF the high side driver, the voltage regulator turns OFF the field circuit.

The PCM monitors the state of the generator turn on signal circuit. The PCM should detect a low generator turn on signal circuit voltage when the key is ON and the engine is OFF, or when the charging system malfunctions. With the engine running, the PCM should detect a high generator turn on signal circuit. The PCM performs key ON and RUN tests to determine the status of the generator turn on signal circuit. During the key ON test, if the PCM detects a high generator turn on signal circuit voltage, DTC P01637 will set. DTC P1637 will also set if, during the RUN test, the PCM detects a low generator turn on signal circuit. When the DTC sets, the PCM will turn on the charge indicator in the IPC.

### Conditions for Running the DTC

• | The ignition is ON.

• | The engine speed is more than 1000 RPM.

### Conditions for Setting the DTC

• | The PCM detects the GEN L-Terminal active with the ignition ON.

• | The PCM detects the GEN L-Terminal inactive with the engine operating.

• | The above conditions are present for 6 seconds.

### Action Taken When the DTC Sets

• | The PCM will record the operating conditions presents when the DTC set as Failure Records data only.

• | The instrument panel cluster (IPC) displays a message.

• | The malfunction indicator lamp (MIL) will not illuminate.

### Conditions for Clearing the DTC

• | The Conditions for Setting the DTC are no longer present.

• | A history DTC will clear after 40 malfunction free ignition cycles.

• | The Powertrain Control Module (PCM) receives the clear code command from the scan tool.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Electrical Connector End Views
1 | Did you perform the Engine Electrical Diagnostic System Check? | -- | Go to Step 2 | Go to Diagnostic System Check - Engine Electrical
2 |

1. Install a scan tool.
2. Idle 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 Step 3

Go to Step 4

3 | Probe the generator battery feed circuit using the test lamp connected to ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems. Does the test lamp illuminate? | -- | Go to Step 4 | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems
4 | Inspect the terminal contact tension at the generator electrical connector. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? |  | Go to Step 11 | Go to Step 5
5 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector C2. Refer to Powertrain Control Module Replacement in Engine Controls-8.1L.
3. Test for a high resistance or open in 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 6

Go to Step 8

6 | Test or a high resistance or open in the generator circuit from terminal B at the generator harness connector to battery ground using the DMM. Refer to Testing for Continuity in Wiring Systems . Does the DMM indicate continuity? | -- | Go to Step 7 | Go to Step 9
7 | Inspect the terminal contact tension at the PCM harness connector. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems . Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9
8 | Repair the open or high resistance in the generator circuit. Refer to Wiring Repairs in Wiring Systems . Is the repair complete? | -- | Go to Step 13 | --
9 | Repair the short to ground in the generator circuit. Refer to Wiring Repairs in Wiring Systems. Is the repair complete? | -- | Go to Step 13 |
10 | Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls-8.1L. Is the action complete? | -- | Go to Step 13 | --
11 |

1. Remove 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. Refer to Measuring Voltage in Wiring Systems.

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

10 V

Go to Step 13

Go to Step 12

12 | Replace the generator. Refer to Generator Replacement . Is the action complete? | -- | Go to Step 13 | --
13 |

1. Select the diagnostic trouble code (DTC) option and the Clear DTC Information option using the scan tool.
2. Operate the vehicle within the Conditions for Running this DTC as specified in the supporting text, if applicable.

Does the DTC reset?

--

System OK

Go to Step 2