HVAC MTC
B102F-REAR BLEND REQUEST INPUT CIRCUIT HIGH
For a complete wiring diagram, refer to the Wiring Information Electrical Diagrams.
Theory of Operation
The Rear A/C Heater Module works in conjunction with the Front A/C Heater Module to control the output of the rear blend door. The rear control for the blend door is a potentiometer (sometimes referred to as a Pot) that is a variable resistor that changes when turned in either direction. The potentiometer is a three terminal resistor with a sliding contact that forms an adjustable voltage divider. The Front A/C Heater Module monitors the voltage from the Rear A/C Heater Control and if the voltage drops below or rises above a predetermined range a DTC will set.
- When Monitored:
With the ignition on.
- Set Condition:
If the rear blend control potentiometer is out of range towards the high voltage threshold. This DTC has a maturing time of five seconds and a de-maturing time of 10 seconds. If the DTCs status changes from active to stored it will stay in memory for 100 ignition cycles.
Always perform the HVAC Pre-Diagnostic Troubleshooting procedure before proceeding. Initial Inspection and Diagnostic Overview.
1. CHECK IF THE DTC IS ACTIVE
1. Ignition on, engine not running.
2. With the scan tool, read HVAC DTCs.
Is this DTC active?
Yes
- Go To 3
No
- Go To 2
2. ATTEMPT TO RESET THE DTC
1. Ignition on, engine not running.
2. Erase HVAC DTCs, turn the ignition off for 30 seconds and back on.
3. Using the rear controls, slowly turn the blend control knob completely in both directions.
Does this DTC reset?
Yes
- Go To 3
No
- Go To 10
3. CHECK THE REAR A/C HEATER MODULE
1. Turn the ignition off to the lock position.
2. Disconnect the Rear A/C Heater Module harness connector.
3. While slowly turning the blend control knob completely in both directions, measure the resistance of the Rear A/C Heater Module Potentiometer between the (C22) Rear Blend Sense circuit and the (C931) Rear Blend Sense Return circuit in the Rear A/C Heater Module.
NOTE: Normal resistive value of the Rear A/C Heater Module Potentiometer is 2.2k to 10k Ohms ±20%.
Is the resistive value change fluid or consistent and within limits?
Yes
- Go To 4
No
- Replace the Rear A/C Heater Module.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
4. CHECK THE (C22) REAR BLEND SENSE CIRCUIT FOR A SHORT TO VOLTAGE
1. Turn the ignition off to the lock position.
2. Disconnect the Front A/C Heater Module C1 harness connector.
3. Disconnect the Rear A/C Heater Module harness connector.
4. Ignition on, engine not running.
5. Measure the voltage of the (C22) Rear Blend Sense circuit.
Is there any voltage present?
Yes
- Repair the (C22) Rear Blend Sense circuit for a short to voltage.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
No
- Go To 5
5. CHECK THE (C800) REAR BLEND SENSE SUPPLY CIRCUIT FOR A SHORT TO VOLTAGE
1. Measure the voltage of the (C800) Rear Blend Sense Supply circuit.
Is there and voltage present?
Yes
- Repair the (C800) Rear Blend Sense Supply circuit for a short to voltage.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
No
- Go To 6
6. CHECK THE (C931) REAR BLEND SENSE RETURN CIRCUIT FOR A SHORT TO VOLTAGE
1. Measure the voltage of the (C931) Rear Blend Sense Return circuit.
Is there any voltage present?
Yes
- Repair the (C931) Rear Blend Sense Return circuit for a short to voltage.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
No
- Go To 7
7. CHECK THE (C22) REAR BLEND SENSE CIRCUIT FOR AN OPEN
1. Turn the ignition off to the lock position.
2. Measure the resistance of the (C22) Rear Blend Sense circuit between the Front A/C Heater Module C1 harness connector and the Rear A/C Heater Module harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 8
No
- Repair the (C22) Rear Blend Sense circuit for an open.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
8. CHECK THE (C800) REAR BLEND SENSE SUPPLY CIRCUIT FOR AN OPEN
1. Measure the resistance of the (C800) Rear Blend Sense Supply circuit between the Front A/C Heater Module C1 harness connector and the Rear A/C Heater Module harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Go To 9
No
- Repair the (C800) Rear Blend Sense Supply circuit for an open.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
9. CHECK THE (C931) REAR BLEND SENSE RETURN CIRCUIT FOR AN OPEN
1. Measure the resistance of the (C931) Rear Blend Sense Return circuit between the Front A/C Heater Module C1 harness connector and the Rear A/C Heater Module harness connector.
Is the resistance below 5.0 Ohms?
Yes
- Replace the Front A/C Heater Module.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
No
- Repair the (C931) Rear Blend Sense Return circuit for an open.
- Perform the HVAC VERIFICATION TEST. HVAC Verification Test.
10. 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 schematics as a guide, inspect the wiring and connectors specific to this circuit.
4. Check for an intermittent condition by inspecting the related wiring harness for chafed, pierced, pinched, or partially broken wires.
5. Check the connectors for broken, bent, pushed out, spread, corroded, or contaminated terminals.
6. 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.