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 Descriptors

DTC B3933 13: Evaporator Air Temperature Voltage High Sensor
DTC B3933 14: Evaporator Air Temperature Voltage Low Sensor

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Evaporator Sensor Signal | B3933 13 | B3933 14 | B3933 14 | --
Evaporator Low Reference Signal | -- | 1 | -- | --
1. A/C compressor will not engage

### Circuit/System Description

The HVAC control module supplies the evaporator temperature sensor with a low reference circuit and 5-volt signal circuit. The HVAC control module determines the voltage drop across the sensor, which is proportional to temperature. When the refrigerant temperature is low the sensor resistance and voltage signal are high. When the refrigerant temperature is high the sensor resistance and voltage signal are low. The sensor works in conjunction with a switch to meter the flow of refrigerant therefore preventing the freezing of moisture that condenses on the evaporator. An evaporator with little refrigerant will starve causing insufficient cooling. An evaporator flooded with refrigerant will also cause poor cooling when there is too much liquid refrigerant that cannot vaporize quickly.

### Conditions for Running the DTC

The ignition is turned ON.

### Conditions for Setting the DTC

The HVAC control module detects the evaporator temperature sensor signal circuit is less than 0.443 volt or greater than 4.55 volts.

### Action Taken when the DTC Sets

The air conditioning (A/C) compressor will be disabled.

### Conditions for Clearing the DTC

• | The DTC will become history if the HVAC control module no longer detects a failure.

• | The history DTC will clear after 50 fault-free ignition cycles.

• | The DTC can be cleared with a scan tool.

### Reference Information

#### Schematic Reference

HVAC Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

• | Air Temperature Description and Operation

• | Air Delivery 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 Testing

1. Ignition OFF, disconnect the evaporator temperature sensor harness connector at the evaporator temperature sensor.
2. Ignition OFF, test for less than 1 ohm between the low reference circuit terminal B and ground of the evaporator temperature sensor.

⇒ | If greater than the specified range, test the low reference circuit terminal for an open/high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, verify the evaporator air temperature sensor parameter is greater than 4.55 volts.

⇒ | If less than the specified range, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the HVAC control module.

4. Install a 3A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B of the sensor. Verify the evaporator air temperature sensor voltage parameter is less than 0.433 volt.

⇒ | If greater than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

5. If all circuits test normal, test or replace the evaporator temperature sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Air Conditioning (A/C) Refrigerant Low Temperature Sensor Replacement

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