Pinpoint Test E: DTC B1255 or DTC B1257
Climate Control System
Pinpoint Tests
Pinpoint Test E: DTC B1255 or DTC 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 - Electronic Automatic Temperature Control (EATC) or HVAC module - Dual Automatic Temperature Control (DATC) through circuit RH104 (BU/BN). A 5-volt reference voltage is supplied to the ambient air temperature sensor from the DATC/EATC module 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 - EATC
- HVAC module - DATC
PINPOINT TEST E: DTC B1255 OR DTC B1257
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E1 CHECK THE SENSOR RESISTANCE
- Ignition OFF.
- Disconnect: Ambient Temperature Sensor C132.
- Carry out the ambient temperature sensor component test. Ambient Temperature Sensor
- Does the ambient temperature sensor test OK?
Yes
GO to E2.
No
INSTALL a new ambient temperature sensor. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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E2 CHECK THE HVAC MODULE OUTPUT VOLTAGE
- Ignition ON.
- Press the AUTO button.
- Measure the voltage between ambient temperature sensor C132-A, circuit VH407 (YE/GN), harness side and C132-B, circuit RH104 (BU/BN), 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 E7.
No
If diagnosing DTC B1255, GO to E3.
If diagnosing DTC B1257, GO to E5.
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E3 CHECK CIRCUIT VH407 (YE/GN) FOR AN OPEN
- Ignition OFF.
- Disconnect: HVAC Module - DATC C2356b or HVAC Module - EATC C228b.
EATC
- NOTE: EATC systems only.
- Measure the resistance between HVAC module - EATC C228b-17, circuit VH407 (YE/GN), harness side and ambient temperature sensor C132-A, circuit VH407 (YE/GN), harness side.
DATC
- NOTE: DATC systems only.
- Measure the resistance between HVAC module - DATC C2356b-17, circuit VH407 (YE/GN), harness side and ambient temperature sensor C132-A, circuit VH407 (YE/GN), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to E4.
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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E4 CHECK CIRCUIT RH104 (BU/BN) FOR AN OPEN
EATC
- NOTE: EATC systems only.
- Measure the resistance between HVAC module - EATC C228b-3, circuit RH104 (BU/BN), harness side and ambient temperature sensor C132-B, circuit RH104 (BU/BN), harness side.
DATC
- NOTE: DATC systems only.
- Measure the resistance between HVAC module - DATC C2356b-3, circuit RH104 (BU/BN), harness side and ambient temperature sensor C132-B, circuit RH104 (BU/BN), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to E7.
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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E5 CHECK CIRCUITS VH407 (YE/GN) AND RH104 (BU/BN) FOR A SHORT TOGETHER
- Ignition OFF.
- Disconnect: HVAC Module - DATC C2356b or HVAC Module - EATC C228b.
- Measure the resistance between ambient temperature sensor C132-A, circuit VH407 (YE/GN), harness side and C132-B, circuit RH104 (BU/BN), harness side.
- Is the resistance greater than 10,000 ohms?
Yes
GO to E6.
No
REPAIR circuits VH407 (YE/GN) 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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E6 CHECK CIRCUIT VH407 (YE/GN) FOR A SHORT TO GROUND
EATC
- NOTE: EATC systems only.
- Measure the resistance between HVAC module - EATC C228b-17, circuit VH407 (YE/GN), harness side and ground.
DATC
- NOTE: DATC systems only.
- Measure the resistance between HVAC module - DATC C2356b-17, circuit VH407 (YE/GN), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to E7.
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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E7 CHECK THE MODULE CONNECTION
- Carry out the HVAC Module Cold Boot Process. HVAC Module Cold Boot Process
- Carry out the HVAC Module - Electronic Automatic Temperature Control (EATC) and HVAC Module - Dual Automatic Temperature Control (DATC) On-Demand Self Test.
- Operate the system.
- Does the concern 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. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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