Pinpoint Test D: DTC B1251 Or B1253
Climate Control System
Pinpoint Tests
Pinpoint Test D: DTC B1251 or B1253
Refer to Wiring Diagram Set 55, Automatic Climate Control System for schematic and connector information. Diagrams By Number
Normal Operation
Under normal operation, the in-vehicle air temperature sensor receives a ground from the HVAC module. The sensor varies its resistance with the temperature. As the temperature rises, the resistance falls. As the temperature falls the resistance rises. The HVAC module measures this resistance to determine the temperature at the sensor.
- DTC B1251 (Air Temperature Internal Sensor Circuit Open) - The module senses no voltage drop on the sensor reference voltage circuit, indicating an open circuit.
- DTC B1253 (Air Temperature Internal Sensor Circuit Short to Ground) - The module senses excessive voltage drop on the sensor reference voltage circuit, indicating a short directly to ground.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- In-vehicle air temperature sensor
- HVAC module - Dual Automatic Temperature Control (DATC)
PINPOINT TEST D: DTC B1251 OR B1253
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D1 CHECK THE SENSOR RESISTANCE
- Ignition OFF.
- Disconnect: In-Vehicle Temperature Sensor C233.
- Measure the resistance between the in-vehicle temperature sensor terminals.
- Is the resistance within the specified values for these temperature ranges: 10-20°C (50-68°F), 37,000-58,000 ohms; 20-30°C (68-86°F), 24,000-37,000 ohms; 30-40°C (86-104°F), 16,000-24,000 ohms?
Yes
GO to D2.
No
GO to D7.
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D2 CHECK THE HVAC MODULE SENSOR OUTPUT VOLTAGE
- Ignition ON.
- Press the AUTOMATIC button.
- Measure the voltage between in-vehicle temperature sensor C233-1, circuit VH414 (GN/BU), harness side and C233-2, circuit RH104 (BU/BN), harness side.
- Is the voltage between 4.7 and 5.1 volts?
Yes
INSTALL a new in-vehicle temperature sensor. TEST the vehicle for normal operation. If code returns, INSTALL a new HVAC module - DATC. TEST the system for normal operation.
No
For DTC B1251, GO to D3.
For DTC B1253, GO to D5.
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D3 CHECK CIRCUIT VH414 (GN/BU) FOR AN OPEN
- Ignition OFF.
- Disconnect: HVAC Module - DATC C228A.
- Measure the resistance between HVAC module - DATC C228A-7, circuit VH414 (GN/BU), harness side and in-vehicle temperature sensor C233-1, circuit VH414 (GN/BU), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to D4.
No
REPAIR circuit VH414 (GN/BU) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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D4 CHECK CIRCUIT RH104 (BU/BN) FOR AN OPEN
- Measure the resistance between HVAC module - DATC C228A-6, circuit RH104 (BU/BN), harness side and in-vehicle temperature sensor C233-2, circuit RH104 (BU/BN), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to D7.
No
REPAIR circuit RH104 (BU/BN) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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D5 CHECK CIRCUITS VH414 (GN/BU) AND RH104 (BU/BN) FOR A SHORT TOGETHER
- Ignition OFF.
- Disconnect: HVAC Module - DATC C228A.
- Disconnect: HVAC Module - DATC C228B.
- Measure the resistance between in-vehicle temperature sensor C233-1, circuit VH414 (GN/BU), harness side and C233-2, circuit RH104 (BU/BN), harness side.
- Is the resistance greater than 10,000 ohms?
Yes
GO to D6.
No
REPAIR circuits VH414 (GN/BU) and RH104 (BU/BN) for a short together. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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D6 CHECK CIRCUIT VH414 (GN/BU) FOR A SHORT TO GROUND
- Measure the resistance between ground and HVAC module - DATC C228A-7, circuit VH414 (GN/BU), harness side.
- Is the resistance greater than 10,000 ohms?
Yes
GO to D7.
No
REPAIR circuit VH414 (GN/BU) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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D7 CHECK THE HVAC MODULE CONNECTION
- Disconnect and inspect the HVAC module connectors for:
- corrosion.
- pushed-out terminals.
- damaged terminals.
- Connect and correctly seat all the HVAC module connectors.
- Clear the DTCs.
- Operate the system.
- Enter the following diagnostic mode on the scan tool: Self-Test - HVAC Module.
- Do the DTCs return?
Yes
INSTALL a new HVAC module. TEST the system for normal operation.
No
The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
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