Pinpoint Test O: DTC B1255 or B1257
Climate Control System
Pinpoint Tests
Pinpoint Test O: DTC B1255 or B1257
Refer to Wiring Diagram Set 54, Manual Climate Control System for schematic and connector information. Diagrams By Number
Normal Operation
Under normal operation, the ambient 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 B1255 (Air Temperature External Sensor Circuit Open) - The module senses no voltage drop on the sensor reference voltage circuit, indicating an open circuit.
- DTC B1257 (Air Temperature External 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
- Ambient air temperature sensor
- HVAC module
PINPOINT TEST O: DTC B1255 OR B1257
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O1 CHECK THE SENSOR RESISTANCE
- Ignition OFF.
- Disconnect: Ambient Temperature Sensor C132.
- Measure the resistance between the ambient temperature sensor C132 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 O2.
No
INSTALL a new ambient temperature sensor. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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O2 CHECK THE SENSOR OUTPUT VOLTAGE
- Ignition ON.
- Measure the voltage between ambient temperature sensor C132-1, circuit VH407 (YE/GN), harness side and C132-2, circuit RH111 (GY/BU), harness side.
- Is the voltage between 4.7 and 5.1 volts?
Yes
INSTALL a new ambient temperature sensor. CLEAR the DTCs. REPEAT the self-test. If code returns, GO to O8.
No
If diagnosing DTC B1255, GO to O3.
If diagnosing DTC B1257, GO to O6.
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O3 CHECK CIRCUIT VH407 (YE/GN) FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: HVAC Module C2357A.
- Ignition ON.
- Measure the voltage between HVAC module C2357A-2, circuit VH407 (YE/GN), harness side and ground.
- Is any voltage present?
Yes
REPAIR circuit VH407 (YE/GN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
No
GO to O4.
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O4 CHECK CIRCUIT VH407 (YE/GN) FOR AN OPEN
- Ignition OFF.
- Measure the resistance between HVAC module C2357A-2, circuit VH407 (YE/GN), harness side and ambient temperature sensor C132-1, circuit VH407 (YE/GN), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to O5.
No
REPAIR circuit VH407 (YE/GN) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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O5 CHECK CIRCUIT RH111 (GY/BU) FOR AN OPEN
- Measure the resistance between HVAC module C2357A-10, circuit RH111 (GY/BU), harness side and ambient temperature sensor C132-2, circuit RH111 (GY/BU), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to O8.
No
REPAIR circuit RH111 (GY/BU) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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O6 CHECK CIRCUIT VH407 (YE/GN) FOR A SHORT TO CIRCUIT RH111 (GY/BU)
- Ignition OFF.
- Disconnect: HVAC Module C2357A.
- Measure the resistance between ambient temperature sensor C132-1, circuit VH407 (YE/GN), harness side and C132-2, circuit RH111 (GY/BU), harness side.
- Is the resistance greater than 10,000 ohms?
Yes
GO to O7.
No
REPAIR circuit VH407 (YE/GN) for a short to circuit RH111 (GY/BU). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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O7 CHECK CIRCUIT VH407 (YE/GN) FOR A SHORT TO GROUND
- Measure the resistance between HVAC module C2357A-2, circuit VH407 (YE/GN), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to O8.
No
REPAIR circuit VH407 (YE/GN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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O8 CHECK THE HVAC MODULE CONNECTION
- Disconnect and inspect the 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. REFER to Climate Control Heating Ventilation Air Conditioning (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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