CAL Transponder and Immobilizer Systems 3 — Questions and Answers
Question 1: What does 'IMMO OFF' refer to in automotive locksmith practice?
- Disabling the key fob remote functions only
- Bypassing or disabling the immobilizer system via ECU modification (Correct answer)
- Switching the vehicle to valet mode
- Resetting all stored key codes to factory
Correct answer: Bypassing or disabling the immobilizer system via ECU modification
IMMO OFF is a technique where the ECU firmware is modified so the vehicle no longer checks for a valid transponder signal, effectively disabling the immobilizer.
Question 2: Which tool function is specifically needed to program a Megamos Crypto (ID48) transponder?
- Standard OBD-II pin-code read
- Crypto calculation using the chip's challenge-response data (Correct answer)
- Direct EEPROM read of the TCU only
- Factory reset through the diagnostic port
Correct answer: Crypto calculation using the chip's challenge-response data
ID48 transponders require specialized crypto calculation tools that can perform the mutual authentication algorithm used by Megamos Crypto chips.
Question 3: What is the function of a 'key learning' or 'key registration' procedure performed via OBD-II?
- To physically cut the key blade profile
- To add a new transponder's ID to the vehicle's authorized list (Correct answer)
- To update the vehicle's firmware
- To reset the odometer to zero
Correct answer: To add a new transponder's ID to the vehicle's authorized list
OBD-II key learning writes the new transponder's unique ID into the immobilizer control module's approved key list.
Question 4: A technician finds that a vehicle requires a 4-digit PIN code before adding new keys via OBD. Where is this PIN typically sourced?
- Stamped on the original key head
- From the vehicle's VIN-based database or EEPROM extraction (Correct answer)
- From the tire pressure sensor module
- From the vehicle's radio code sticker
Correct answer: From the vehicle's VIN-based database or EEPROM extraction
PIN codes for key programming are typically retrieved from a VIN-linked database service or by reading the immobilizer EEPROM directly.
Question 5: Which Honda transponder system uses a 13.56 MHz frequency and is considered a high-security chip?
- Honda HDH transponder
- Texas TI TPMS chip
- Honda G-chip (46E) (Correct answer)
- EM Marine 4100 chip
Correct answer: Honda G-chip (46E)
Honda's G-chip uses 13.56 MHz high-frequency communication and incorporates crypto authentication, making it more secure than low-frequency 125 kHz chips.
Question 6: What happens during the 'challenge-response' phase of a crypto transponder authentication?
- The ECU sends a random number, and the transponder returns an encrypted answer (Correct answer)
- The key sends its ID and the ECU confirms via a simple match
- The BCM cuts power until the correct fixed code is received
- The transponder resets the ECU to allow startup
Correct answer: The ECU sends a random number, and the transponder returns an encrypted answer
In challenge-response authentication, the ECU generates a random challenge; the transponder uses a shared secret key to compute and return the correct encrypted response.
Question 7: A locksmith is asked to add a key to a Toyota with a 4D transponder. Which method is most commonly used when no working key is available?
- Key cutting by code and standard OBD programming
- Dump the immobilizer ECU EEPROM and use a specialized programmer (Correct answer)
- Call the dealership for a new ECU
- Replace the ignition cylinder and relearn all keys
Correct answer: Dump the immobilizer ECU EEPROM and use a specialized programmer
Without a working key, the most reliable method is to read the immobilizer ECU's EEPROM dump and use a transponder tool to generate or write the correct 4D crypto data.
CAL Transponder and Immobilizer Systems 3
What does 'IMMO OFF' refer to in automotive locksmith practice?