GM Service Manual Online
For 1990-2009 cars only

Battery is Undercharged or Overcharged

Step

Action

Value(s)

Yes

No

1

Was the Charging System Check performed?

--

Go to Step 2

Go to Charging System Check

2

  1. Turn OFF all accessories. Connect the generator 4-way connector (if disconnected).
  2. Start the engine and run at 2500 RPM.
  3. Check the voltage across the battery terminals.

Is the voltage within the specified range?

13-16 V

Go to Step 3

Go to Step 5

3

Stop the engine. Perform the battery (parasitic) load test.

Is the parasitic load below the specified value?

22 ma

Go to Charging System Check

Go to Step 4

4

Determine the source of the excessive parasitic drain and repair as necessary.

Is the repair complete?

--

Go to Charging System Check

--

5

Was the voltage across the battery terminals with the engine running at 2500 RPM too low?

--

Go to Step 6

Go to Step 9

6

  1. Disconnect the generator 4-way connector. Turn the ignition switch to the RUN position.
  2. Use a digital multimeter (DMM) to measure the CKT 225 voltage in cavity B of the generator connector.

Is the voltage above the specified value?

12 V

Go to Step 7

Go to Step 10

7

Check CKT 225 between the generator and the VCM for an Intermittent shorted/grounded condition or a poor connection.

Is CKT 225 OK?

--

Go to Step 14

Go to Step 8

8

Repair CKT 225 as necessary. Refer to Wiring Repairs in Wiring Systems.

Is CKT 225 repair complete?

--

Go to Step 15

--

9

Check the Generator 4-way connector for a mis-wired condition in cavity D. This cavity should not be in this vehicle.

Has the mis-wired condition been repaired?

--

Go to Step 15

--

10

  1. Disconnect or backprobe the CKT 225 connector at the VCM
  2. Turn the ignition switch to the RUN position.
  3. Use a DMM to check the voltage output of the VCM to CKT 225.

Is the voltage above the specified value?

12 V

Go to Step 11

Go to Step 12

11

Repair CKT 225 for a shorted, grounded, or open condition. Refer to Wiring Repairs in Wiring Systems.

Is the CKT 225 repair complete?

--

Go to Step 15

--

12

Replace the VCM. Is the repair complete?

--

Go to Step 15

--

13

Replace the generator.

Is the repair complete?

--

Go to Step 15

--

14

  1. Disconnect the negative battery cable.
  2. Disconnect and clean all connections between the positive battery terminal and the generator output terminal. Check all cables for an intermittent open condition.
  3. Disconnect and clean all connections in the ground circuit between the negative battery terminal and the generator housing. Check all cables for an intermittent open condition.
  4. Connect the negative battery cable.

Is the repair complete?

--

Go to Step 15

--

15

  1. Turn OFF all accessories. Connect the generator 4-way connector (if disconnected).
  2. Start the engine and run at 2500 RPM.
  3. Check the voltage across the battery terminals.

Is the voltage within the specified range?

13--16 V

Go to Charging System Check

Go to Step 5