B272B
DTC B272B
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.
DTC Descriptor
DTC B272B 03
- Rear Differential Lock Mode Switch Circuit Below Threshold
DTC B272B 07
- Rear Differential Lock Mode Switch Circuit Above Threshold
Diagnostic Fault Information
Circuit/System Description
The mode switch circuit consists of 3 or 4 modes depending on how the vehicle is equipped with the transfer case shift control module only monitoring the rear differential lock portion of the switch. The transfer case shift control module supplies a regulated 5 volts, DC to the switch through the 5-volt regulator circuit. The current travels through the resistor of the currently pressed mode button. The current is then returned to the transfer case shift control module through the switch signal circuit.
The transfer case shift control module constantly monitors this signal voltage to determine the condition of the mode switch circuit.
When each of the modes are selected they will complete a circuit through their own specific resistor while the button is pressed. The transfer case shift control module continuously monitors the switch input to determine if the Differential Lock mode was selected by the driver.
Conditions for Running the DTC
* The ignition is ON.
* The system voltage is 9-18 volts.
Conditions for Setting the DTC
* The system constantly monitors the voltage on switch signal circuit.
* If the system detects a voltage level under 0.44 volt or greater than 0.56 volts for 60 seconds, the DTC is logged.
Action Taken When the DTC Sets
* All differential lock requests will be ignored.
* The SERVICE 4WD indicator will remain illuminated for the remainder of the current ignition cycle.
* Failure Records will be stored.
Conditions for Clearing the DTC
* The transfer case shift control module will clear the current DTC if the condition for setting the DTC is not currently present.
* A history DTC will clear after 40 warm up cycles without a fault present.
* History DTCs can be cleared using a scan tool.
Reference Information
Schematic Reference
Transfer Case Control Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
Description and Operation
Transfer Case Description and Operation (Description and Operation)
Electrical Information Reference
* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information.
Circuit/System Testing
The 5 volt reference circuit and the switch signal will have to be checked for shorts to ground, opens, high resistance, and shorts to voltage by following the below listed steps.
1. Reference the mode switch supply voltage with a scan tool.
• The scan tool should indicate 4.8-5.2 volts. If the scan tool indicates the voltage is within this specification then with a jumper wire short the switch signal circuit pin C1 pin 1 on the switch to the 5 volt reference circuit C1 pin 9 on the switch. If the rear differential lock switch return voltage on the scan tool measures 4.8-5.2 volts then replace the switch.
2. If the rear differential lock switch return does not read 4.8-5.2 volts check the rear differential lock switch signal circuit and the 5 volt reference circuits for a short to ground, short to voltage, open, or high resistance.
• If no shorts or high resistance are found on the switch signal or 5 volt reference circuits then replace the transfer case shift control module.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
* Accessory Switch Replacement (Service and Repair)
* Control Module References (Programming and Relearning) for TCSCM replacement, setup, and programming
Repair Verification
Clear the DTCs and operate the vehicle so that the DTC runs, if the DTC runs and passes then the repair was successful.