B048E

DTC B048D or B048E

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 Descriptors

DTC B048D 01
Auxiliary Heater Temperature Command Circuit Short to Battery

DTC B048D 06
Auxiliary Heater Temperature Command Circuit Low Voltage/Open

DTC B048E 00
Auxiliary Heater System Malfunction

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 [1][2]Electrical Diagrams

Connector End View Reference
Component Connector End Views

Description and Operation
Automatic HVAC Description and Operation 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 set.
2. If DTC is present, refer to Electrical Auxiliary Heater Control Circuit Malfunction.
3. Verify that DTC B048E 00 is not set.
4. 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. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 2 X1 and ground.
3. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
4. Test for less than 0.3 V between the control circuit terminal 7 X2 at the K33 HVAC Control Module harness connector and ground.
5. If greater than the specified range, test the control circuit for a short to voltage.
6. Ignition OFF, test for infinite resistance between the control circuit terminal 7 X2 at the K33 HVAC Control Module harness connector and ground.
7. If less than the specified value, test the control circuit for a short to ground.
8. Test for less than 5 ohm 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.
9. If greater than the specified value, test the control circuit for an open/high resistance.
10. If all circuits test normal, replace the E40 Electrical Auxiliary Heater and verify the DTC does not reset.

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.
3. If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.
4. Verify that a test lamp illuminates between the B+ circuit terminal 1 X2 and ground circuit terminal 1 X3.
5. If the test lamp does not illuminate, test the ground circuit for an open/high resistance.
6. Verify that a test lamp illuminates between the ignition circuit terminal 2 X1 and ground circuit terminal 1 X3.
7. If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
8. Test for less than 0.3 V between the signal circuit terminal 5 X2 at the K33 HVAC Control Module harness connector and ground.
9. If greater than the specified range, test the signal circuit for a short to voltage.
10. Ignition OFF, test for infinite resistance between the signal circuit terminal 5 X2 at the K33 HVAC Control Module harness connector and ground.
11. If less than the specified value, test the signal circuit for a short to ground.
12. Test for less than 5 ohm 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.
13. If greater than the specified value, test the circuit for an open circuit/high resistance.
14. If all circuits test normal, replace the E40 Electrical Auxiliary Heater and verify the DTC does not reset.

Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

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