Pinpoint Test D: DTC B1255 Or B1257
Climate Control System
Pinpoint Tests
Pinpoint Test D: DTC B1255 or B1257
Refer to Wiring Diagram Set 55, Automatic 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 - Dual Automatic Temperature Control (DATC) through circuit RH111 (GY/BU). A 5-volt reference voltage is supplied to the ambient air temperature sensor from the HVAC module - DATC through circuit VH407 (YE/GN).
- 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 - DATC
PINPOINT TEST D: DTC B1255 OR B1257
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D1 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 D2.
No
INSTALL a new ambient temperature sensor. CLEAR the DTCs. REPEAT the self test. TEST the system for normal operation.
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D2 CHECK THE SENSOR OUTPUT VOLTAGE
- Ignition ON.
- Press the AUTO button.
- 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 D7.
No
If diagnosing DTC B1255, GO to D3.
If diagnosing DTC B1257, GO to D5.
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D3 CHECK CIRCUIT VH407 (YE/GN) FOR AN OPEN
- Ignition OFF.
- Disconnect: HVAC Module - DATC C228a.
- Measure the resistance between HVAC module - DATC C228a-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 D4.
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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D4 CHECK CIRCUIT RH111 (GY/BU) FOR AN OPEN
- Measure the resistance between HVAC module - DATC C228a-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 D7.
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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D5 CHECK CIRCUIT VH407 (YE/GN) FOR A SHORT TO CIRCUIT RH111 (GY/BU)
- Ignition OFF.
- Disconnect: HVAC Module - DATC C228a.
- 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 D6.
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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D6 CHECK CIRCUIT VH407 (YE/GN) FOR A SHORT TO GROUND
- Measure the resistance between HVAC module - DATC C228a-2, circuit VH407 (YE/GN), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to D7.
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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D7 CHECK THE MODULE CONNECTION
- Carry out the HVAC Module Cold Boot Process. HVAC Module Cold Boot Process
- Carry out the HVAC Module - Dual Automatic Temperature Control (DATC) On-Demand Self Test. Alternate Diagnostic Methods - HVAC Module - Dual Automatic Temperature Control (DATC) Only
- Operate the system.
- Does the concern return?
Yes
INSTALL a new HVAC module - DATC. 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. CLEAR the DTCs. REPEAT the self test. TEST the system for normal operation.
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