GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 2001 🢒 Catera 🢒 HVAC 🢒 HVAC Systems - Automatic 🢒 DTC 030

Circuit Description

When the water cut-off vacuum solenoid valve is activated it allows vacuum to be applied to the hot water control valve. The control valve prevents heated coolant from entering the heater core when the vacuum is applied.

In the air conditioning mode or when cooler air is requested, the heater and A/C control grounds the coil of the water cut-off vacuum solenoid valve. When the ignition switch is in the ON position, battery voltage is supplied from the heater and A/C control to the solenoid. With voltage supplied and ground provided the solenoid energizes, and allows vacuum to flow to the hot water control valve.

Conditions for Running the DTC

The ignition is turned ON.

Conditions for Setting the DTC
    • Every 200 ms the heater and A/C control continuously monitors CKT 920 for an open or short to ground.
    • CKT 920 stays at or near zero volts.

Action Taken When the DTC Sets
    • Stores a DTC 30 in the heater and A/C control memory.
    • The heater and A/C control does not disable the output.

Conditions for Clearing the DTC
    • The conditions for the fault are no longer present.
    • Using a scan tool.
    • A history DTC will clear after 20 consecutive ignition cycles if the condition for the fault is no longer present.

Diagnostic Aids
    • If condition not present, refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
    • Test the power and ground circuits before replacing the heater and A/C control.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. Listen for an audible click when the water cut-off vacuum solenoid operates. Command both the ON and OFF states. Repeat the commands as necessary.

    2.

  2. Tests for voltage at the coil side of the water cut-off vacuum solenoid. The heater and A/C control supplies power to the coil side of the water cut-off vacuum solenoid.

    3.

  3. Verifies that the heater and A/C control is providing ground to the water cut-off vacuum solenoid.

    4.

  4. Tests if ground is constantly being applied to the water cut-off vacuum solenoid.

Step

Action

Yes

No

Schematic Reference: HVAC Schematics

1

Did you perform the HVAC Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - HVAC Systems - Automatic

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, command the Heating Cutoff Valve Test ON and OFF.

Does the water cut-off vacuum solenoid turn ON and OFF with each command?

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Disconnect the water cut-off vacuum solenoid.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe circuit 939 of the water cut-off vacuum solenoid with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 10

4

  1. Connect a test lamp between circuit 920 of the water cut-off vacuum solenoid and circuit 939 of the water cut-off vacuum solenoid.
  2. With a scan tool, command the Heating Cutoff Valve Test ON and OFF .

Does the test lamp turn ON and OFF with each command?

Go to Step 8

Go to Step 5

5

Does the test lamp remain illuminated with each command?

Go to Step 7

Go to Step 6

6

Test circuit 920 of the water cut-off vacuum solenoid for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

7

Test circuit 920 of the water cut-off vacuum solenoid for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 9

8

Inspect for poor connections at the water cut-off vacuum solenoid. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 11

9

Inspect for poor connections at the harness connector of the heater and A/C control. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 13

Go to Step 12

10

Repair circuit 939 of the water cut-off vacuum solenoid. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 13

--

11

Replace the water cut-off vacuum solenoid. Refer to Vacuum Electrical Solenoid Replacement - Hot Water Bypass Control .

Did you complete the replacement?

Go to Step 13

--

12

Important: Perform the recalibration procedure for the heater and A/C control .

Replace the heater and A/C control. Refer to HVAC Control Module Replacement .

Did you complete the replacement?

Go to Step 13

--

13
  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK