B3935
DTC B3935
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 B3935 57
- Transponder Authentication Error
Circuit/System Description
When an ignition key is inserted into the ignition lock cylinder and the ignition is switched ON, the transponder embedded in the head of the key is energized by the exciter coils surrounding the ignition lock cylinder. The energized transponder transmits a signal that contains its unique value, which is received by the theft deterrent module (TDM). The TDM then compares this value to a value stored in memory. This stored value is the learned key code. If the value is correct, the TDM will send the fuel continue password via the serial data circuit to the engine control module (ECM). If the learned key code does not match or a transponder value is not received, the TDM will send the start disable password to the ECM.
Conditions for Running the DTC
* Ignition is in the Accessory or Run position.
* A valid transponder value has been read.
Conditions for Setting the DTC
The TDM is unable to communicate or learn the key.
Action Taken When the DTC Sets
* Vehicle starting will be disabled.
* The security indicator will be illuminated.
Conditions for Clearing the DTC
* A current DTC will be cleared when a valid transponder value has been read and authenticated.
* A history DTC will be cleared after 100 malfunction-free ignition cycles.
Diagnostic Aids
In some instances, RF devices attached to a keychain or otherwise in close proximity of the ignition cylinder may cause interference in the immobilizer system and lead to a no-start condition. Some common RF devices that may be attached to a keychain are Speedpass gas station payment device, swipe devices used to gain access locked gates or 24-hour gyms, or other "smart" keys.
These RF devices interfere with the communication between the transponder located in the key and the TDM. The immobilizer systems operates at a frequency of 125 kHz. RF devices that operate in the 120 to 135 kHz range, or a multiplier of these frequencies, are most likely to cause interference. If interference occurs, DTC B3055, B3060, or B3935 may be set.
If interference is suspected, removed the suspect device from the keychain and attempt to start the vehicle. If vehicle starting occurs with the device removed, instruct the customer to remove the device from the keychain to prevent further occurrences. It may also be necessary to inspect all of the customers keychains if the concern is intermittent and doesn't occur with every key.
Reference Information
Schematic Reference
Immobilizer Schematics (Immobilizer Schematics)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Immobilizer Description and Operation (Immobilizer)
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
Scan Tool Reference
Control Module References (Programming and Relearning) for scan tool information
Circuit/System Verification
Important: Interference from an RF device located on the keychain may cause this DTC to set. Remove any RF devices from the keychain before proceeding with the diagnostic.
Replace the suspected inoperative or malfunctioning key. DTC B3935 should not reset and the vehicle should start.
If the replacement key results in the resetting of DTC B3935, replace the TDM.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Important: Because of how vehicle key information and theft deterrent passwords are stored within the TDM, the Set Up a New Theft Deterrent Module procedure must be performed prior to the removal and replacement of the TDM if the vehicle keys are being reused. Performing the setup procedure first allows the scan tool to extract the key information and passwords from the old TDM prior to its removal. Failure to perform this step will result in the failure to learn the existing vehicle keys and new vehicle keys will be required when replacing the TDM.
If the existing vehicle keys are not being reused, the TDM is to be replaced prior to performing of the setup procedure.
* Replacing Keys (Testing and Inspection)
* Control Module References (Programming and Relearning) for TDM replacement, setup, and programming