For 1990-2009 cars

### Insufficient Heating of the Rear Seat Area

Inspect for one of the following conditions:

• | Inspect for a faulty auxiliary coolant bypass pump and auxiliary coolant bypass pump switch.

• | A faulty blower motor. Replace a faulty blower motor.

• | A faulty blower circuit. Repair or replace faulty wires or connections.

1. Inspect for the incorrect operation of the controls. Advise the driver to use high blower speed in order to force air into the rear of the passenger compartment.
2. Inspect for an obstruction on the floor. Inspect for the following conditions under the front seat:

• | Bulky objects.

• | Torn insulation.

### Insufficient Heating

1. Inspect the duct work for the following conditions:

• | The proper insulation.

• | Obstructions.

2. Inspect the blower operation.
3. Inspect the following components for the proper installation and the proper operation:

• | The temperature lever.

• | The temperature motor.

### Circuit Description

The auxiliary coolant bypass pump provides additional coolant flow for the heater core. The operating temperature range of the auxiliary coolant bypass pump is between 2°C (36°F) and 8°C (47°F). The auxiliary coolant bypass pump is powered by ignition voltage through the auxiliary coolant bypass pump switch. The ground is provided by the ground circuit.

### Test Description

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

1. The auxiliary coolant bypass pump operates only between 2°C (36°F) and 8°C (47°F).

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference : HVAC Compressor Control Schematics in HVAC Manual. DEFINITION: The auxiliary coolant bypass pump is inoperative.
1 | Did you perform the HVAC Diagnostic System Check? | Go to Step 2 | Go to Diagnostic System Check
2 | Important: For auxiliary coolant bypass pump operation, the ambient air temperature must be between 2°C (36°F) and 8°C (47°F). Turn ON the ignition with the engine OFF. Does the auxiliary coolant bypass pump operate? | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems | Go to Step 3
3 |

1. Disconnect the auxiliary coolant bypass pump.
2. Probe the auxiliary coolant bypass pump control circuit of the auxiliary coolant bypass pump with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 4

Go to Step 5

4 | Probe the auxiliary coolant bypass pump control circuit of the auxiliary coolant bypass pump with a test lamp that is connected to the ground circuit of the auxiliary coolant bypass pump. Does the test lamp illuminate? | Go to Step 6 | Go to Step 7
5 |

1. Disconnect the auxiliary coolant bypass pump switch.
2. Probe the ignition 1 voltage circuit of the auxiliary coolant bypass pump switch with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

Go to Step 10

Go to Step 8

6 |

1. Connect the auxiliary coolant bypass pump.
2. Connect a 10 amp fused jumper between the ignition 1 voltage circuit and the auxiliary coolant bypass pump control circuit of the auxiliary coolant bypass switch.

Does the auxiliary coolant bypass pump operate?

Go to Step 13

Go to Step 9

7 | Repair the ground circuit of the auxiliary coolant bypass pump. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 14 | --
8 | Repair the Ignition 1 voltage circuit of the auxiliary coolant bypass pump switch. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 14 | --
9 | Repair auxiliary coolant bypass pump control circuit of the auxiliary coolant bypass pump. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 14 | --
10 | Inspect for poor connections at the harness connector of the auxiliary coolant bypass pump. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 12
11 | Inspect for poor connections at the harness connector of the auxiliary coolant bypass pump switch. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 14 | Go to Step 13
12 | Replace the auxiliary coolant bypass pump. Refer to Auxiliary Coolant Pump Replacement . Did you complete the replacement? | Go to Step 14 | --
13 | Replace the auxiliary coolant bypass pump switch. Refer to Auxiliary Coolant Bypass Pump Switch Replacement . Did you complete the replacement? | Go to Step 14 | --
14 | Operate the system in order to verify the repair. Did you correct the condition? | System OK | Go to Step 3