3. Troubleshooting

This troubleshooting section applies to starting and running problems caused by faults in the ignition system, including the Hall sender, the ignition control unit, the power stage, the coil, the distributor cap and rotor, and the spark plug wires. Troubleshooting for the diesel glow plug system is covered in 6. Diesel Glow Plug System.

The ignition system's primary function is to provide a properly timed high-voltage spark. The distributor's basic timing adjustment gives the Hall sender and the electronic system its baseline ignition timing. Depending on the system, the Hall sender signal is monitored by the ignition control unit, the knock sensor control unit, or the Digifant or Motronic control unit. The control unit in turn switches the coil primary circuit, causing the coil to discharge high voltage to the spark plugs through the distributor cap and spark plug wires. In this sensitive electronic ignition system, corroded or loose connections may interfere with any part of this function.

A complete failure of the ignition system to produce spark at the spark plugs is self-evident as an ignition system problem. For other problems such as rough idle, misfiring, or poor starting, the cause is not so clear. Start by testing and evaluating the ignition system, but if no ignition problems are discovered, proceed elsewhere. Inadequate engine compression or a malfunctioning fuel system will cause similar problems. See ENGINE for information on checking compression.

Checking the fuel system is especially important in Digifant and CIS-E Motronic systems where fuel and ignition control are integrated into one control unit. For more general help in determining what section may best apply, see FUNDAMENTALS at the front of the manual.

Cars with the CIS-E Motronic, Digifant II (some California models only), or Digifant I engine management system feature on-board diagnosis (OBD) circuitry in the control unit to detect faults in the system during normal operation. When activated, the system displays faults as a number code which corresponds to a particular component or function of the system which should be checked.

Your authorized Volkswagen dealer's service department is equipped with an analyzer which plugs into a special test connection in the car's wiring harness. It can retrieve and interpret the fault codes, and also perform electronic checks of the knock control reference sensor, the Hall sender, and the knock sensors.