GM Service Manual Online
For 1990-2009 cars only

Object Number: 406560  Size: SF
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The PCM controlled lamps are powered through the instrument panel battery positive voltage or ignition positive voltage circuit. The PCM turns ON the bulb, the LED, or the driver info center indicator by supplying a path to ground through the PCM.

Diagnostic Aids

A PCM controlled lamp ON at all times most likely indicates that a condition is present which requires the attention of the vehicle operator.

Low Oil Level Lamp - will illuminate for about a minute after the ignition has been turned ON when the PCM tests for low oil level and the engine oil level switch indicates that a low oil level condition exists. The PCM determines whether or not to test for low oil level based on the difference between the engine coolant temperature at the last shutdown and engine coolant temperature at startup. This is to ensure that the oil has drained back into the sump before testing. When the ignition is first turned ON, the PCM commands the Low Oil Level lamp ON for a brief period of time to test the bulb.

Check for the following conditions:

    • Poor connection at PCM.
        Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • Damaged harness.
        Inspect the wiring harness for damage. If the harness appears to be OK, disconnect the PCM and turn the ignition ON . Observe a voltmeter connected to the affected PCM output circuit while moving connectors and wiring harnesses related to the PCM output circuit. A change in voltage will indicate the location of the fault.
    • Engine oil level switch circuit. Refer to DTC P1653 Low Engine Oil Level Lamp Control Circuit .

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Chart.

  1. Normally, ignition feed voltage should be present on the output control circuit with the PCM disconnected and the ignition turned ON.

  2. Checks for a shorted component or a short to B+ on the output control circuit. Either condition would result in a measured current of over 500 milliamps. Also checks for a component that is going open while being operated, resulting in a measured current of 0 milliamps.

  3. Checks for a short to voltage on the lamp control circuit.

  4. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.

PCM Controlled Lamps

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Was the Instrument Cluster System check in Electrical Diagnosis performed?

--

Go to Step 3

Go to Instrument Cluster System Check .

3

  1. Turn OFF the ignition.
  2. Disconnect the PCM.
  3. Turn ON the ignition.
  4. Using a J 39200 Digital Multimeter, measure voltage between the affected lamp control circuit at the PCM harness connector and ground.

Is voltage near the specified value?

B+

Go to Step 4

Go to Step 7

4

  1. Connect the digital multimeter to measure current between the affected lamp control circuit and ground.
  2. Monitor the current reading on the digital multimeter for at least 2 minutes.

Does the current reading remain between the specified values?

0.05 -0.5 Amp

(50-500 mA)

Go to Step 12

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the instrument panel cluster (leave the PCM disconnected).
  3. Turn ON the ignition.
  4. Measure voltage between the affected lamp control circuit and ground.

Is voltage at the specified value?

0V

Go to Step 15

Go to Step 6

6

Locate and repair the short to voltage in the affected PCM output circuit. Refer to Wiring Repairs .

Is action complete?

--

Go to Step 17

--

7

Check the ignition feed fuse for the instrument panel cluster indicator lamps.

Is the fuse blown?

--

Go to Step 8

Go to Step 9

8

  1. Locate and repair the short to ground in the ignition feed circuit for the instrument panel cluster indicator lamps. Refer to

    Cell 10: IGN 1 Fuse, Ignition Switch


    Object Number: 342244  Size: FS
    Power and Grounding Component Views
    Cell 10: IGN 3 Fuse, Ignition Switch (Buick)
    Cell 10: Battery
    Cell 10: Engine Compartment Junction Block
    Cell 10: Engine Compartment Junction Block
    Cell 10: Battery
    ,

    Cell 81: IP Fuse Block


    Object Number: 341914  Size: FS
    Instrument Panel, Gages, and Console Component Views
    Cell 81: Fuel Tank Unit
    Power Distribution Schematics
    Power Distribution Schematics
    Power Distribution Schematics
    Power Distribution Schematics
    Ground Distribution Schematics
    Ground Distribution Schematics
    Data Link Connector Schematics
    Handling ESD Sensitive Parts Notice
    , or Wiring Repairs .
  2. Replace the fuse.

Is action complete?

--

Go to Step 17

--

9

  1. Disconnect the instrument panel cluster.
  2. Turn ON the ignition.
  3. Measure voltage between the ignition feed circuit for the instrument panel cluster indicator lamps and ground.

Is voltage near the specified value?

B+

Go to Step 10

Go to Step 14

10

  1. Check the affected lamp control circuit for an open or a short to ground.
  2. If a problem is found repair as necessary. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 17

Go to Step 11

11

  1. Check the affected lamp control circuit and the ignition feed circuit for a poor connection at the instrument panel cluster or at the PCM.
  2. If a problem is found, replace the loose terminal(s). Refer to Intermittents and Poor Connections Diagnosis and Repairing Connector Terminals .

Was a problem found?

--

Go to Step 17

Go to Step 15

12

  1. Turn OFF the ignition.
  2. Reconnect the PCM and disconnect the instrument panel cluster.
  3. Turn ON the ignition.
  4. Connect a test lamp between the affected lamp control circuit and the ignition feed circuit at the instrument panel cluster harness connector.
  5. Using the scan tool outputs test function, cycle the affected lamp ON and OFF.

Does the test lamp flash ON and OFF?

--

Go to Diagnostic Aids

Go to Step 13

13

  1. Check the affected lamp control circuit for a poor connection at the PCM.
  2. If a problem is found, replace the loose terminal. Refer to Intermittents and Poor Connections Diagnosis and Repairing Connector Terminals .

Was a problem found?

--

Go to Step 17

Go to Step 16

14

Locate and repair open in the ignition feed circuit to the instrument panel cluster indicator lamps. Refer to Wiring Repairs .

Is action complete?

--

Go to Step 17

--

15

Replace the instrument panel cluster. Refer to Instrument Cluster Replacement .

Is action complete?

--

Go to Step 17

--

16

Important: The replacement PCM must be programmed.

Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is action complete?

--

Go to Step 17

--

17

Operate the affected lamp using the scan tool output tests function.

Does the affected lamp operate properly?

--

System OK

Go to Step 3