For 1990-2009 cars

### 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 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 Setting the DTC

• | If a short circuit to battery is detected on a low side driver, the controller automatically protects the low side driver by disabling all low side outputs.

• | A short to battery has been detected on CKT 920.

### Action Taken When the DTC Sets

• | Stores a DTC 31 in the heater and A/C control memory.

• | The fault detection process is repeated 3 times at a fixed interval of 70 ms to allow for debouncing.

• | The heater and A/C control disables the output internally.

### 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 the DTC is a history or an intermittent. Try performing the tests shown while moving wiring harnesses and connectors, this can often cause the malfunction to appear.

• | When moving related harnesses and harness connectors, visually/physically inspect wiring and connectors for the following:

- | Dirt or corrosion on the terminals. The terminals must be clean and free of any foreign material which could impede proper terminal contact.

- | Damaged connector body, exposing the terminals to moisture and dirt, as well as not maintaining proper terminal orientation with the component or mating connector.

- | Wire insulation which is rubbed through, causing an intermittent short as the bare area touches other wiring or parts of the vehicle.

• | Check the power and ground circuits before replacing the heater and A/C control.

### Test Description

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

1. This step determines if CKT 920 is shorted to battery.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Was the Air Delivery System Check performed? | -- | Go to Step 2 | Go to HVAC Air Delivery System Check
2 |

1. Remove the heater and A/C control.
2. Disconnect connector C2.
3. Using a DMM, measure and record the voltage at terminal 21 of connector C2.
4. Turn ON the ignition.
5. Measure and record the voltage at the same terminal.

Are both voltage measurements within the specified value?

Less than 0.1 V

Go to Step 3

Go to Step 4

3 | The problem may be intermittent at this time. Repeat step 2 but monitor the DMM while moving related harnesses and harness connectors. Was a problem found and repaired? | -- | Go to Step 5 | Go to Step 7
4 | Locate and repair short to B+ in CKT 920. Is the repair complete? | -- | Go to Step 5 | --
5 |

1. Reassemble connectors removed.
2. Install the scan tool and clear codes.
3. Recheck for DTC 31.

Is a current DTC 31 set?

--

Go to Step 6

Go to HVAC Air Delivery System Check

6 | Replace and program the heater and A/C control. Refer to Control Assembly Replacement . Is the replacement and programming complete? | -- | Go to HVAC Air Delivery System Check | --
7 |

1. Disconnect the recirculation solenoid valve connector.
2. Measure the resistance of the solenoid.

Does the resistance reading indicate shorted solenoid windings?

(NOTE: normal resistance of the solenoid is 36.4 ohms.)

--

Go to Step 8

Go to Step 5

8 | Replace the recirculation solenoid valve. Is the replacement complete? | -- | Go to Step 5 | --