Pinpoint Test E: DTC B1255 Or DTC B1257
Climate Control System
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 A/C ambient temperature sensor receives a ground from the HVAC module through circuit 3059 (YE/LG). A 5-volt reference voltage is supplied to the A/C ambient temperature sensor from the HVAC module through circuit 3061 (LB/OG).
- DTC B1255 Ambient Temperature Sensor Open Circuit - The module senses no voltage drop on the sensor reference voltage circuit, indicating an open circuit.
- DTC B1257 Ambient Temperature 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
- A/C ambient temperature sensor
- HVAC module
PINPOINT TEST E: DTC B1255 OR DTC B1257
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E1 CHECK THE AMBIENT TEMPERATURE SENSOR RESISTANCE
- Ignition OFF.
- Disconnect: Ambient Temperature Sensor C132.
- Measure the resistance between the ambient 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 E2.
No
INSTALL a new ambient air 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 AUTOMATIC button.
- Measure the voltage between ambient temperature sensor C132-1, circuit 3061 (LB/OG), harness side and C132-2, circuit 3059 (YE/LG), 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. TEST the system for normal operation. If the code returns, INSTALL a new HVAC module. TEST the system for normal operation.
No
If diagnosing DTC B1255, GO to E3.
If diagnosing DTC B1257, GO to E5.
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E3 CHECK CIRCUIT 3061 (LB/OG) FOR AN OPEN
- Ignition OFF.
- Disconnect: HVAC Module C228a.
- Measure the resistance between HVAC module C228a-7, circuit 3061 (LB/OG), harness side and ambient temperature sensor C132-1, circuit 3061 (LB/OG), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to E4.
No
REPAIR circuit 3061 (LB/OG) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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E4 CHECK CIRCUIT 3059 (YE/LG) FOR AN OPEN
- Measure the resistance between HVAC module C228a-4, circuit 3059 (YE/LG), harness side and ambient temperature sensor C132-2, circuit 3059 (YE/LG), harness side.
- Is the resistance less than 5 ohms?
Yes
GO to E7.
No
REPAIR circuit 3059 (YE/LG) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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E5 CHECK CIRCUITS 3061 (LG/OG) AND 3059 (YE/LG) FOR A SHORT TOGETHER
- Ignition OFF.
- Disconnect: HVAC Module C228a.
- Measure the resistance between ambient temperature sensor C132-1, circuit 3061 (LB/OG), harness side and C132-2, circuit 3059 (YE/LG), harness side.
- Is the resistance greater than 10,000 ohms?
Yes
GO to E6.
No
REPAIR circuit 3061 (LG/OG) for a short to circuit 3059 (YE/LG). CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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E6 CHECK CIRCUIT 3061 (LG/OG) FOR A SHORT TO GROUND
- Measure the resistance between HVAC module C228a-7, circuit 3061 (LG/OG), harness side and ground.
- Is the resistance greater than 10,000 ohms?
Yes
GO to E7.
No
REPAIR circuit 3061 (LG/OG) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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E7 CHECK MODULE CONNECTION
- Carry out the HVAC Module Cold Boot Process. HVAC Module Cold Boot Process
- Carry out the HVAC Module On-Demand Self Test. HVAC Module 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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