Pinpoint Test N: The HVAC Module Does Not Respond To The Scan Tool
Communications Network
Pinpoint Tests
Pinpoint Test N: The HVAC Module Does Not Respond To The Scan Tool
Refer to Wiring Diagram Set 14, Module Communications Network for schematic and connector information. Diagrams By Number
Refer to Wiring Diagram Set 54, Manual Climate Control System for schematic and connector information. Diagrams By Number
Refer to Wiring Diagram Set 55, Automatic Climate Control System for schematic and connector information. Diagrams By Number
Normal Operation
The HVAC module communicates with the scan tool through the Medium Speed Controller Area Network (MS-CAN). Circuits VDB06 (GY/OG) (MS-CAN +) and VDB07 (VT/OG) (MS-CAN -) provide the network connection to the HVAC module. The HVAC module shares the MS-CAN with the Smart Junction Box (SJB), the ACM, the Driver Seat Module (DSM), the Rear Entertainment Module (RETM), the Satellite Digital Audio Receiver System (SDARS) module, the Liftgate/Trunk Module (LTM) and the Instrument Cluster (IC). Voltage for the HVAC module is provided by circuits CBP37 (WH) and SBP15 (WH/RD). Circuit GD111 (BK/BU) provides ground.
This pinpoint test is intended to diagnose the following:
- Fuse
- Wiring, terminals or connectors
- HVAC module
PINPOINT TEST N: THE HVAC MODULE DOES NOT RESPOND TO THE SCAN TOOL
NOTICE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
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N1 CHECK THE HVAC MODULE VOLTAGE SUPPLY CIRCUITS FOR AN OPEN
- Ignition OFF.
- Disconnect: HVAC - EATC Module C228a or HVAC - EMTC module C2357a.
- Ignition ON.
- Measure the voltage between the HVAC - EATC module C228a-12 or HVAC - EMTC module C2357a-12, circuit CBP37 (WH), harness side and ground; and between the HVAC - EATC module C228a-13 or HVAC - EMTC module C2357a-13, circuit SBP15 (WH/RD), harness side and ground.
- Are the voltages greater than 10 volts?
Yes
GO to N2.
No
VERIFY the SJB fuses 15 (10A) or 37 (10A) are OK. If OK, REPAIR the circuit in question. If not OK, Refer to the Wiring Diagrams to identify the possible causes of the short circuit. CLEAR the DTCs. REPEAT the network test with the scan tool.
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N2 CHECK THE GROUND CIRCUIT FOR AN OPEN
- Ignition OFF.
- Measure the resistance between the HVAC - EATC module C228a-23 or HVAC - EMTC module C2357a-23, circuit GD111 (BK/BU), harness side and ground.
- Is the resistance less than 5 ohms?
Yes
GO to N3.
No
REPAIR the circuit. CLEAR the DTCs. REPEAT the network test with the scan tool.
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N3 CHECK THE MS-CAN CIRCUITS BETWEEN THE HVAC MODULE AND THE DLC FOR AN OPEN
- Measure the resistance between the HVAC - EATC module C228a-25 or HVAC - EMTC module C2357a-25, circuit VDB06 (GY/OG), harness side and the DLC C251-3, circuit VDB06 (GY/OG), harness side.
- Measure the resistance between the HVAC - EATC module C228a-26 or HVAC - EMTC module C2357a-26, circuit VDB07 (VT/OG), harness side and the DLC C251-11, circuit VDB07 (VT/OG), harness side.
- Are the resistances less than 5 ohms?
Yes
GO to N4.
No
REPAIR the circuit in question. CLEAR the DTCs. REPEAT the network test with the scan tool.
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N4 CHECK FOR CORRECT HVAC MODULE OPERATION
- Disconnect all the HVAC module connectors.
- Check for:
- corrosion
- damaged pins
- pushed-out pins
- Connect all the HVAC module connectors and make sure they seat correctly.
- Operate the system and verify the concern is still present.
- Is the concern still present?
Yes
INSTALL a new HVAC module. CLEAR the DTCs. REPEAT the network test with the scan tool.
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 network test with the scan tool.
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