For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC B048D 01: Auxiliary Heater Temperature Command Circuit Short to Battery
DTC B048D 06: Auxiliary Heater Temperature Command Circuit Short to Ground or Open
DTC B084E 00: Auxiliary Heater System Malfunction

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Electrical Auxiliary Heater Control | B048D 06 | B048D 06 | B048D 01 | --
Electrical Auxiliary Heater Signal | B048E 00 | B048E 00 | B048E 00 | --

### Circuit/System Description

The HVAC control module sends a pulse width modulation (PWM) signal to the electrical auxiliary heater, if the interior temperature is too low and additional heat is requested. The request signal from the HVAC control module, battery positive, ignition and ground circuits enable the electrical auxiliary heater to operate. Through the signal circuit the electrical auxiliary heater sends via a PWM signal the current status to the HVAC control module.

### Conditions for Running the DTC

• | Ignition ON.

• | The HVAC control module is ON.

• | The electrical auxiliary heater is ON.

### Conditions for Setting the DTC

#### B048D 01

The voltage at the HVAC control module output to the electrical auxiliary heater is always high.

#### B048D 06

The voltage at the HVAC control module output to the electrical auxiliary heater is always low or floating.

#### B048E 00

The feedback signal of the electrical auxiliary heater does not correspond with the requested PWM signal.

### Action Taken When the DTC Sets

The electrical auxiliary heater is inoperative.

### Conditions for Clearing the DTC

The feedback signal of the electrical auxiliary heater corresponds with the requested PWM signal.

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Manual HVAC Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Verify that DTC B048D 01 or B048D 06 is not present.

⇒ | If DTC is present, refer to Electrical Auxiliary Heater Control Circuit Malfunction.

2. Verify that DTC B048E 00 is not present.

⇒ | If DTC is present, refer to Electrical Auxiliary Heater Signal Circuit Malfunction.

### Circuit/System Testing

#### Electrical Auxiliary Heater Control Circuit Malfunction.

1. Ignition OFF, disconnect the X2 harness connector at the K33 HVAC Control Module and the X1 harness connector at the E40 Electrical Auxiliary Heater.
2. Test for less than 0.3 V between the control circuit terminal 7 (X2) at the K33 HVAC Control Module harness connector and ground.

⇒ | If greater than the specified range, test the control circuit for a short to voltage.

3. Ignition OFF, test for infinite resistance between the control circuit terminal 7 (X2) at the K33 HVAC Control Module harness connector and ground.

⇒ | If less than the specified range, test the control circuit for a short to ground.

4. Test for less than 5 Ω between the K33 HVAC Control Module control circuit terminal 7 (X2) and control circuit terminal 1 (X1) at the E40 Electrical Auxiliary Heater harness connector.

⇒ | If greater than the specified value, test the control circuit for an open/high resistance.

5. If all circuits test normal, replace the E40 Electrical Auxiliary Heater and verify the DTC does not reset.

⇒ | If the DTC resets, replace the K33 HVAC Control Module.

#### Electrical Auxiliary Heater Signal Circuit Malfunction.

1. Ignition OFF, disconnect the X2 harness connector at the K33 HVAC Control Module and the harness connectors at the E40 Electrical Auxiliary Heater.
2. Ignition ON, verify that a test lamp illuminates between the B+ circuit terminal 1 (X2) at the E40 Electrical Auxiliary Heater harness connector and ground.

⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Verify that a test lamp illuminates between the B+ circuit terminal 1 (X2) and ground circuit terminal 2 (X2).

⇒ | If the test lamp does not illuminate, test the ground circuit for an open/high resistance.

4. Verify that a test lamp illuminates between the ignition circuit terminal 2 (X1) and ground circuit terminal 2 (X2).

⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

5. Test for less than 0.3 V between the signal circuit terminal 5 (X2) at the K33 HVAC Control Module harness connector and ground.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage.

6. Ignition OFF, test for infinite resistance between the signal circuit terminal 5 (X2) at the K33 HVAC Control Module harness connector and ground.

⇒ | If less than the specified range, test the signal circuit for a short to ground.

7. Test for less than 5 Ω between the K33 HVAC Control Module signal circuit terminal 5 (X2) and signal circuit terminal 4 (X1) at the E40 Electrical Auxiliary Heater harness connector.

⇒ | If greater than the specified value, test the circuit for an open/high resistance.

8. If all circuits test normal, replace the E40 Electrical Auxiliary Heater and verify the DTC does not reset.

⇒ | If the DTC resets, replace the K33 HVAC Control Module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Auxiliary Heater Core Replacement

• | Control Module References for HVAC control module replacement, setup, and programming