GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Firebird 🢒 Engine 🢒 Engine Controls - 5.7L 🢒 Powertrain Control Module Controlled Generator Diagnosis

Object Number: 585396 Size: SF
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.

  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

--