HVAC, MTC

B1027-12-REAR CONTROL HEAD BLOWER REQUEST INPUT - CIRCUIT SHORT TO BATTERY





For a complete wiring diagram refer to the Wiring Information .

Theory of Operation

The Rear A/C Heater Control works in conjunction with the A/C Heater Control to control the rear blower motor, rear temperature control and rear mode control. The Rear A/C Heater Control is constantly monitored by the A/C Heater Control for proper operation. If the monitored signal circuits are out of a calibrated range at DTC will set. For further information Description and Operation.

- When Monitored:
With the ignition on.

- Set Condition:
If the A/C Heater Control detects a short to voltage or open on the Rear Blower Signal circuit. If a valid voltage is detected the DTC will change from active to stored and stay in the controllers memory for 100 consecutive ignition cycles.





Always perform the HVAC Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.

NOTE: This DTC must be active for the results of this test to be valid. Do not perform this test if this DTC is stored. Refer to HVAC System Test (ATC) for stored DTC test procedures. Stored Lost Communication DTCs

1. VERIFY THE DTC IS ACTIVE
1. Ignition on, engine not running.
2. With the scan tool, erase HVAC DTCs.
3. Turn the ignition off, wait 10 seconds, and turn the ignition on.

NOTE: Make sure the Rear Control Lockout on the A/C Heater Control is not turned on.

4. With the scan tool, read HVAC DTCs after 60 seconds.

Does the scan tool display this DTC as active?

Yes

- Go To 2

No

- Go To 7

2. CHECK FOR OTHER REAR REQUEST CIRCUIT HIGH DTCS
1. With the scan tool, read HVAC DTCs.

Are there any Rear Blend or Mode circuit DTCs also present and Active?

Yes

- Go To 4

No

- Go To 3

3. CHECK THE (C11) REAR BLOWER SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE




1. Turn the ignition off to the lock position.
2. Disconnect the A/C Heater Control C2 harness connector.
3. Disconnect the Rear A/C Heater Control harness connector.
4. Ignition on, engine not running.
5. Measure the voltage of the (C11) Rear Blower Signal circuit.

Is there any voltage present?

Yes

- Repair the (C11) Rear Blower Signal circuit for a short to voltage.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Go To 6

4. CHECK THE (C955) SIGNAL GROUND CIRCUIT FOR A SHORT TO VOLTAGE




1. Turn the ignition off to the lock position.
2. Disconnect the A/C Heater Control C2 harness connector.
3. Disconnect the Rear A/C Heater Control harness connector.
4. Ignition on, engine not running.
5. Measure the voltage of the (C955) Signal Ground circuit.

Is there any voltage present?

Yes

- Repair the (C955) Signal Ground circuit for a short to voltage.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Go To 5

5. CHECK THE (C955) SIGNAL GROUND CIRCUIT FOR AN OPEN




1. Turn the ignition off to the lock position.
2. Measure the resistance of the (C955) Signal Ground circuit between the A/C Heater Control C2 harness connector and the Rear A/C Heater Control harness connector.

Is the resistance below 1.0 Ohm?

Yes

- Go To 6

No

- Repair the (C955) Signal Ground circuit for an open.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

6. CHECK THE HVAC CONTROL MODULES
1. Ignition on, engine not running.
2. With the scan tool, erase HVAC DTCs.
3. Turn the ignition off to the lock position.
4. Reconnect the A/C Heater Control C2 harness connector. NOTE: The Rear A/C Heater Control harness connector should still be disconnected.

5. Ignition on, engine not running.
6. With the scan tool, read HVAC DTCs.

Does the scan tool display this DTC?

Yes

- Replace and program the A/C Heater Control. A/C And Heater Control - Removal.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Replace the Rear A/C Heater Control. A/C And Heater Control - Removal.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

7. CHECK THE WIRING AND CONNECTORS
1. The conditions necessary to set the DTC are not present at this time.
2. With the scan tool, check the Environmental Data to help identify the conditions in which the DTC was set.
3. Using the wiring diagrams as a guide, check all related splices and connectors for signs of water intrusion, corrosion, pushed out or bent terminals, and correct pin tension.
4. Wiggle the wiring and connectors while checking for shorted and open circuits.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.

No

- Test complete.