Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic strategy. |
DTC Descriptor
DTC B1020: Auxiliary Electronic Control Unit (ECU) PerformanceDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
A/C Request Switch | -- | -- | -- | B1020 |
Mode Switch (Potentiometer) | -- | -- | -- | B1020 |
Rear Defogger Switch Signal | -- | -- | -- | B1020 |
Recirculation Switch | -- | -- | -- | B1020 |
Circuit Description
The DTC B1020 code monitors the performance (stuck button or faulty mode air delivery potentiometer) switches located directly on the HVAC control head. They are the following:
| • | A/C Request |
| • | Rear Defogger |
| • | Recirculation |
| • | Mode Air Delivery Selector |
The DTC B1020 is communicated from the HVAC control module to the engine control module (ECM) (hybrid) or body control module (BCM) (non- hybrid) over the pulse width modulated signal (PWM) on the A/C request circuit for the A/C request button. The DTC B1020 is communicated from the HVAC control module to the ECM over the pulse width modulated signal (PWM) on the rear defogger switch signal circuit for the rear defogger button. The Recirculation switch on the HVAC control module communicates directly through the recirc control A and Control B circuits to the recirculation actuator to offer fresh air or recirculation of passenger compartment air. The Mode potentiometer button selector on the HVAC control head communicates directly with the Mode Actuator floor, panel, or defrost actuators. The PWM duty cycle falls within 75-85 percent range which indicates a stuck button or faulty mode potentiometer switch on the HVAC control head.
The ECM will monitor the request circuit for the following:
| • | A short to ground |
| • | A short to voltage |
| • | An open circuit |
| • | A stuck request button on the HVAC control head |
Conditions for Running the DTC
| • | The ignition voltage is between 9-18 volts. |
| • | The engine speed is more than 80 RPM. |
| • | The HVAC control module driver transitions from ON to OFF or from OFF to ON. |
Conditions for Setting the DTC
The ECM detects a faulty mode air delivery potentiometer switch or stuck A/C request, rear defogger, or recirculation switch (button) on the HVAC control head. The following shows the invalid duty cycle range.
75-85 percent
Action Taken When the DTC Sets
| • | The ECM will not illuminate the malfunction indicator lamp (MIL). |
| • | The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data. |
Conditions for Clearing the DTC
| • | A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Diagnostic Aids
| Important: Be sure to verify that the ECM engine grounds are secure and clean. |
| • | If DTC B1020 cannot be duplicated, reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition. |
| • | If the condition is not present, refer to Testing for Intermittent Conditions and Poor Connections . |
Reference Information
Schematic Reference
Connector End View
Description and Operation
Electrical Information Reference
Scan Tool Reference
Circuit System Verification
Mode Select Switch Button
Place the blower switch in the MAX speed position. Place the mode switch in each mode position. The air flow should flow sufficiently from each mode position selected. If the air does not flow correctly from the vents go to mode select mode switch diagnostics.
A/C Request Switch Button
Ignition ON, observe the ECM (hybrid) or BCM on (non-hybrid) scan tool A/C Request parameter while pressing the A/C request switch of the HVAC control head. The scan tool reading should change between Yes and No A/C request value. If the scan tool A/C Request parameter is not correct go to the A/C request switch diagnostics.
Rear Defogger Switch Button
Ignition ON, observe the BCM scan tool data display request parameter while pressing the rear defog switch of the HVAC control head. The scan tool reading should change between Off and On request value. If the Rear Defogger Switch scan tool parameter is not correct go to the rear defogger switch diagnostics.
Recirculation Switch Button
Ignition ON, place the blower motor switch at the MAX speed position. Place the mode switch in the Vent position. Place the recirc switch in the ON (recirc) position. Observe the recirc door. Place the recirc switch in the OFF position (fresh air). The recirc door should move from recirc to the outside air position. If the recirc door does not move go to recirculation switch diagnostics.
Circuit System Testing
Mode Select Switch
- Place the blower switch in the MAX speed position.
- Place the mode switch in each mode position.
| ⇒ | The air flow should flow sufficiently from each mode position selected. If the air does not flow correctly from the vents. |
| ⇒ | If the test lamp remains always ON or always OFF during either of the commands, test both control circuits for a short to voltage, short to ground, or an open/high resistance. If the circuits test normal, replace the HVAC control module. |
A/C Request Switch
- Ignition OFF, disconnect the HVAC harness connector at the A/C switch.
- Test for less than 1.0 ohm of resistance between the HVAC control module ground circuit terminal C1 pin 12 and ground.
- Ignition ON, verify the scan tool ECM A/C request parameter is No or open.
- Install a 3A fused jumper wire between the signal circuit terminal C1 pin 8 and the ground circuit terminal C1 pin 12. Verify the scan tool ECM A/C request switch parameter is YES or closed.
| ⇒ | If greater than the specified range, test the ground circuit for an open/high resistance. |
| ⇒ | If not the specified value, test the A/C request signal circuit terminal HVAC control module terminal C1 pin 8 for a short to ground. If the circuit tests normal, replace the HVAC control module. |
| ⇒ | If not the specified value, test the A/C request signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module. |
Rear Defogger Switch
Ignition ON, verify the scan tool BCM Rear Defog parameter. While pressing the rear defog switch from on to off. If the specified value does not change with the command, refer to DTC B0285 or B0286 .
A/C Recirculation Switch
- Ignition OFF, disconnect the recirculation actuator at the actuator.
- Ignition ON, connect a test lamp between the recirc door control A Connector C1 terminal 3 and recirc door control B connector C1 terminal 2.
- Place the recirculation actuator in the OFF and ON position. The test lamp should turn ON and OFF with each command.
| ⇒ | If the test lamp remains always ON or always OFF during either of the commands, test both control circuits for a short to voltage, short to ground, or an open/high resistance. If the circuits test normal, replace the HVAC control module. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for HVAC replacement, setup, and programming
