GM Service Manual Online
For 1990-2009 cars only

Step

Action

Value(s)

Yes

No

1

Was the charging system check performed?

--

Go to Step 2

Go to Starting System Check

2

Inspect fuse 18 located in the underhood accessory wiring junction block.

Is the GEN fuse open?

--

Go to Step 3

Go to Step 4

3

  1. Replace fuse 18.
  2. Start the engine.
  3. Turn ON several vehicle accessories, such as headlamps and A/C.
  4. Stop the engine.
  5. Turn OFF all the vehicle electrical accessories.
  6. Inspect fuse 18 again.

Is fuse 18 open again?

--

Go to Step 7

Go to Step 4

4

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the generator connector.
  3. Turn the ignition switch ON.
  4. Connect a scan tool to the Data Link Connector (DLC).
  5. On the scan tool, perform the following:
  6. • Select: Powertrain Control Module (PCM).
    • Select: Special Functions.
    • Select: Engine Output Controls.
    • Select: GEN L Terminal.
    • Command the generator ON.
  7. Using J 39200 , measure the voltage between the generator harness connector terminal B and ground.

Is the measured voltage within the specified range?

5 V

Go to Step 5

Go to Step 8

5

Using J 39200 , measure the voltage between the generator BAT terminal (CKT 2) and ground.

Is the voltage measured within the specified range?

B+ (10-14 V)

Go to Step 6

Go to Step 9

6

  1. Turn the ignition switch to the OFF position.
  2. Reconnect the generator connector.
  3. Verify all the vehicle electrical accessories are OFF.
  4. Start the engine and let it run at idle speed.
  5. Using J 39200 , measure the voltage between the battery positive and negative terminals.

Is the voltage measured within the specified range?

13-16 V

Go to Step 12

Go to Step 7

7

  1. Inspect for short to ground in CKT 2740.
  2. If CKT 2740 is not shorted to ground, then replace the generator. Go to Generator Replacement for the service procedure.
  3. Recheck the system.

Is the repair complete?

--

Go to Charging System Check

--

8

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the PCM connector C2.
  3. Using J 39200 , measure the resistance between the PCM harness connector C2 terminal 61 and the generator harness connector terminal B.

Is the resistance measured within the range specified?

Less than 2 ohms

Go to Step 10

Go to Step 11

9

  1. Inspect for a poor connection or an open in CKT 2.
  2. Inspect for a poor ground between the generator housing and the engine. Repair as needed.
  3. Recheck the system.

Is the repair complete?

--

Go to Charging System Check

--

10

  1. The Powertrain Control Module (PCM) is not enabling CKT 225, thus disabling the generator. Go to Powertrain On Board Diagnostic (OBD) System Check .
  2. Recheck the system.

Is the repair complete?

--

Go to Charging System Check

--

11

  1. Repair an open or a poor connection in CKT 225.
  2. Recheck the system.

Is the repair complete?

--

Go to Charging System Check

--

12

  1. Load test the generator. Go to Generator Not Operating Properly .
  2. If the generator electrical test determines the generator output is within specifications, then the instrument cluster is faulty causing the charge indicator light to stay on. Go to Diagnostic System Check - Instrument Cluster .
  3. Recheck the system.

Is the repair complete?

--

Go to Charging System Check

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