For 1990-2009 cars

### Circuit Description

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

The ECM monitors the state of the generator turn on signal circuit. With the engine running, the ECM should detect a high generator turn on signal circuit.

### DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P2500 Generator L-Terminal Circuit Low Voltage

### Conditions for Running the DTC

• | No generator, crankshaft position (CKP) sensors, or camshaft position (CMP) sensor DTCs are set.

• | The engine is running.

• | The generator has not been commanded OFF by the ECM or scan tool.

### Conditions for Setting the DTC

The ECM detects a low signal voltage on the generator turn on signal circuit for at least 15 seconds.

### Action Taken When the DTC Sets

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

• | The ECM will store the conditions present when the DTC set as Fail Records data only.

• | The ECM will send a class 2 serial data message to the instrument panel cluster (IPC) and driver information center (DIC) to illuminate the charge indicator or display a charging message.

### Conditions for Clearing the MIL/DTC

• | The conditions for setting DTC P2500 are not present.

• | The DTC can be cleared by using the scan tool Clear DTC Information function.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Starting and Charging Schematics Connector End View Reference: Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 |

1. Install a scan tool.
2. Start the engine.
3. With a scan tool, observe the GEN - F Terminal Signal parameter in the ECM data list .

Does the scan tool indicate that the GEN - F Terminal parameter is within the specified range?

5-100%

Go to Testing for Intermittent Conditions and Poor Connections

Go to Step 3

3 |

1. Turn OFF the ignition.
2. Disconnect the generator harness connector.
3. Start the engine.
4. Measure the voltage between the generator turn on signal circuit of the generator harness connector and a good ground.

Is the voltage within the specified range?

4.5-5.5 V

Go to Step 5

Go to Step 4

4 | Test the generator turn on signal circuit for a short to ground or open. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 6
5 | Inspect for poor connections at the harness connector of the generator. Refer to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Charging System Test
6 | Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Connector Repairs . Did you find and correct the condition? | -- | Go to Step 8 | Go to Step 7
7 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 8 | --
8 |

1. Review and record the scan tool Fail Records data.
2. Use the scan tool in order to clear the DTC.
3. Operate the vehicle within the conditions for running DTC P2500.
4. Using the scan tool, observe the specific DTC information for DTC P2500 until the test runs.

Does the scan tool indicate that DTC P2500 failed?

--

Go to Step 2

System OK