Service Information

Captiva

DTC B3935

Diagnostic Instructions

•	Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

•	Review Strategy Based Diagnosis for an overview of the diagnostic approach.

•	Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC B3935 57: Transponder Authentication Error

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 energised by the exciter coils surrounding the ignition lock cylinder. The energised 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 pre-release password via the serial data circuit to the engine control module (ECM). If the transponder value does not match the learned key code 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 transponder value is valid and matches the value stored in the TDM memory.

•	The transponder calculation to the challenge from the TDM does not match the TDM calculation.

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 or when a scan tool is used to clear DTCs.

Diagnostic Aids

In some instances, RF devices attached to a key chain or otherwise in close proximity of the ignition cylinder may cause interference in the immobiliser system and lead to a no-start condition. Some common RF devices that may be attached to a key chain are Speedpass petrol station payment device, swipe devices used to gain access to 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 immobiliser 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 key chain and attempt to start the vehicle. If vehicle starting occurs with the device removed, instruct the customer to remove the device from the key chain to prevent further occurrences. It may also be necessary to inspect all of the customers key chains if the concern is intermittent and doesn't occur with every key.

Reference Information

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

Important: Interference from an RF device located on the key chain may cause this DTC to set. Remove any RF devices from the key chain 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 after completing the diagnostic procedure.

•	Replacing Keys

•	Control Module References for theft deterrent module replacement, setup, and programming