GM Service Manual Online
For 1990-2009 cars only

Object Number: 388523  Size: MF
Cell 20: Power, Ground, MIL, and DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

Output Driver Modules (ODMs) are used by the PCM to turn on many of the current-driven devices that are needed to control various engine and Transaxle functions. Each ODM is capable of controlling up to 7 separate outputs by applying ground to the device which the PCM is commanding on. The PCM turns on the bulb, LED, or driver info center indicator by supplying a path to ground through the PCM.

Conditions for Running the DTC

The ignition is on.

Conditions for Setting the DTC

    •  An improper voltage level has been detected on the alternator lamp driver circuit.
    •  Above conditions for at least 20 seconds.

Action Taken When the DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

Conditions for Clearing the MIL/DTC

    • The DTC becomes history when the conditions for setting the DTC are no longer present.
    • The history DTC clears after 40 malfunction free warm-up cycles.
    • The PCM receives a clear code command from the scan tool.

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. Conditions which will illuminate each lamp are as follows:

    •  When the engine speed is greater than 1200 RPM and system voltage falls below 10 volts for longer than 10  seconds.
    •  When the generator control circuit remains low for longer than 10 seconds.
    •  When the engine speed is below 2000 RPM and the generator PWM control circuit duty cycle remains low for longer than 20 seconds.
    •  When the engine speed is above 4000 RPM and the generator PWM control circuit duty cycle remains high for longer than 20 seconds.

For diagnosis of the instrument panel, perform the Instrument Cluster System Check .

Check for the following conditions:

Important: :  Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

    •  Poor terminal connection.
         Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems.
    •  Damaged harness.
         Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems.
    •  Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.

Test Description

The numbers below refer to the step numbers on the Diagnostic Table:

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

  2. Checks for a shorted component or a short to battery positive voltage on the output driver circuit. Either condition would result in a measured current of over 1.5 amps. Also checks for a component that is going open while being operated, resulting in a measured current of 0 amps.

  3. Checks for a faulty instrument cluster.

  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. Refer to Powertrain Control Module Replacement/Programming .

Step

Action

Value(s)

Yes

No

1

Was the Powertrain OBD System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Was the instrument cluster system check performed?

--

Go to Step 3

Go to Instrument Cluster System Check

3

  1. Turn the ignition off.
  2. Disconnect the PCM.
  3. Turn the ignition on.
  4. Using J 39200 DMM, measure voltage between the affected PCM output circuit at the PCM harness connector and ground.

Is the voltage near the specified value?

B+

Go to Step 4

Go to Step 7

4

  1. J 39200 DMM to 10 amp scale, install J 39200 DMM to measure current between the affected PCM output circuit and ground.
  2. Monitor the current reading on the J 39200 DMM for at least 2 minutes.

Does the current reading remain between the specified values?

0.05 amp 1.5 mps

Go to Step 12

Go to Step 5

5

  1. Disconnect the instrument panel cluster (leave the PCM disconnected).
  2. Using J 39200 DMM, measure voltage between the affected PCM output circuit and ground.

Is the voltage at the specified value?

0.0V

Go to Step 15

Go to Step 6

6

Locate and repair short to voltage in affected PCM output circuit.

Is the action complete?

--

Go to Step 3

--

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 short to ground in ignition feed circuit for the instrument panel cluster indicator lamps. Refer to Wiring Repairs .
  2. Replace the fuse.

Is the action complete?

--

Go to Step 3

--

9

  1. Disconnect the instrument panel cluster. Refer to Instrument Cluster Replacement .
  2. Turn the ignition on.
  3. Measure voltage between the ignition feed circuit for the instrument panel cluster indicator lamps and ground.

Is the voltage near the specified value?

B+

Go to Step 10

Go to Step 14

10

  1. Check the affected PCM output circuit for an open or a short to ground.
  2. If a problem is found, repair the affected PCM output circuit. Refer to Wiring Repairs .

Was a problem found?

--

Go to Step 3

Go to Step 11

11

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

Was a problem found?

--

Go to Step 3

Go to Step 15

12

  1. Turn the ignition off.
  2. Reconnect the PCM and disconnect the instrument panel cluster.
  3. Turn the ignition on.
  4. Connect a J 35616-200 test lamp between the affected PCM output 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 J 35616-200 test light flash on and off?

--

Go to Diagnostic Aids

Go to Step 13

13

  1. Check the affected PCM output circuit for a poor connection at the PCM.
  2. If a problem is found, replace faulty terminal. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs .

Was a problem found?

--

Go to Step 3

Go to Step 16

14

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

Is the action complete?

--

Go to Step 3

--

15

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

Is the action complete?

--

Go to Step 3

--

16

Important: :  Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Replace the PCM.

Is the action complete?

--

Go to Step 3

--

17

  1. Review and record scan tool Fail Records data.
  2. Clear DTCs.
  3. Operate vehicle within Fail Records conditions as noted.
  4. Using a scan tool, monitor SPECIFIC DTC info for DTC P1637 until the DTC P1637 test runs.

Does scan tool indicate DTC P1637 failed this ignition?

--

Go to Step 3

System OK