Electrical Systems & Control Modules Flashcards

With the battery disconnected, a technician measures resistance between CAN-High and CAN-Low on the drivetrain CAN bus. What reading indicates both termination resistors are intact?

Answer: About 60 ohms

Two 120-ohm terminating resistors in parallel measure about 60 ohms total.

The same CAN resistance check reads about 120 ohms. What is the most likely cause?

Answer: One termination resistor or its circuit is open

Only one 120-ohm resistor is being measured, so the other branch is open.

On a VW wiring diagram, which terminal designation identifies the switched ignition-on positive circuit?

Answer: Terminal 15

Terminal 15 is switched positive with the ignition on; 30 is constant battery positive, 31 is ground, and 50 is the starter.

Which control module in most modern VW vehicles acts as the gateway between the different data bus systems and the diagnostic connector?

Answer: J533

J533 is the data bus diagnostic interface (gateway) that routes messages between bus systems.

A customer reports a dead battery after the car sits for three days. What is the correct first step for measuring quiescent (parasitic) current?

Answer: Connect the meter or clamp, lock the car, and wait for all modules to enter sleep mode before reading

Modules stay awake for a while after shutdown, so the reading is only valid once the bus has gone to sleep.

A relay in a VW fuse/relay panel has pins 30, 85, 86, and 87. Which pins make up the control (coil) circuit?

Answer: 85 and 86

Pins 85 and 86 feed the coil, while 30 and 87 are the switched load contacts.

Why should a stabilized battery charger or power supply be connected when flashing a control module with ODIS?

Answer: A voltage drop during programming can corrupt the update and leave the module inoperable

Low or unstable voltage during a flash can interrupt the write and 'brick' the module.