GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The 2nd brake control solenoid is energized and de-energized by the Powertrain Control Module (PCM). The solenoid controls the orifice control valve which engages and disengages the O/D and 2nd brake. The 2nd brake control solenoid is activated when the reverse clutch is applied or released. The combined action of the solenoid is to control shift timing and shift feel.

Conditions for Setting the DTC

    • Solenoid resistance is 30ohms or lower (short circuit) when the solenoid is energized.
    • Solenoid resistance is 100Kohms or higher (open circuit) when the solenoid is not energized.
    • One driving cycle detection logic.

Action Taken When the DTC Sets

A DTC P1790 is stored, but the Malfunction Indicator Lamp (MIL) does not illuminate.

Diagnostic Aids

Inspect for the following conditions:

    • Faulty electrical circuit/open or short to the ground between the solenoid and the PCM
    • A faulty PCM
    • A faulty Solenoid

An intermittent may be caused by the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Inspect the Powertrain Control Module (PCM) harness connectors for the following conditions:

    • Backed out terminal
    • Improper mating
    • Broken locks
    • Improperly formed or damaged terminals
    • Inadequate terminal-to-wire connections

Perform the following steps if DTC P1790 cannot be duplicated:

  1. Read the information in the freeze frame data.
  2. Use the data to determine the vehicle operating conditions when the DTC was set.

If any wiring repairs need to be made, refer to Repair Procedures in Electrical Diagnosis.

DTC Confirmation Procedure

  1. Turn the ignition switch to LOCK.
  2. Connect the Scan Tool to Data Link Connector (DLC).
  3. Turn the ignition switch to ON.
  4. Use a Scan Tool to clear the following items from the PCM memory:
  5. • The DTC
    • The pending DTC
    • The freeze frame data
  6. Start the engine.
  7. Step firmly on the brake pedal.
  8. Shift the manual selector to Drive (D).
  9. Leave the selector in Drive (D) for 10 seconds.
  10. Accelerate the vehicle in Drive (D).
  11. Keep driving for 60 seconds at 50 km/h (30 mph).
  12. Stop the vehicle.
  13. Use a Scan Tool to inspect DTC P1790.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

  2. This step inspects the condition of the solenoid and the internal electrical harness for damage.

  3. This step inspects for an open or short in the 2ND brake control circuit.

Step

Action

Value(s)

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

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

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls in Engine Controls

2

  1. Install a scan tool.
  2. Turn the ignition to ON, leaving the engine OFF.
  3. Perform the scan tool Clear DTC Information function.
  4. Operate the vehicle within the Freeze Frame conditions as observed.

Does the scan tool display any other DTCs in addition to DTC P1790?

--

Go to applicable DTC table

Go to Step 3

3

  1. Disconnect the transaxle connector.
  2. Use the J 39200 in order to measure the resistance between the ground and the transaxle connector terminal 2.

Is the resistance within the specified value?

11-15ohms at 20°C (68°F)

Go to Step 4

Go to Step 5

4

  1. Connect the transaxle connector.
  2. Disconnect the PCM C2 connector.
  3. Use the J 39200 in order to measure the resistance between ground and the PCM C2 connector terminal 12.

Is the resistance within the specified value?

11-15ohms at 20°C (68°F)

Go to Step 6

Go to Step 7

5

  1. Remove the transaxle oil pan.
  2. Inspect the terminals and the internal harness for damage.
  3. If the terminals and the internal harness are not damaged, replace the solenoid.

Is the action complete?

--

Go to Step 8

--

6

Replace the PCM.

Is the repair complete?

--

Go to Step 8

--

7

Repair the short, open or high resistance in the 2ND brake control solenoid circuit.

Is the action complete?

--

Go to Step 8

--

8

  1. Turn the ignition switch to LOCK.
  2. Reconnect the connector(s).
  3. Perform the DTC Confirmation Procedure.

Are any DTCs displayed on the Scan Tool?

--

Go to the applicable DTC table

System OK