Knock Sensor System Fault Diagnosis

KNOCK SENSOR SYSTEM FAULT DIAGNOSIS (ENGINE CODES HT, RD, PL, 9A)

CIS-E (Engine Codes HT, RD, PL)
The knock sensor control unit on cars with CIS-E fuel injection (engine code HT, RD, and PL) has a fault memory which records and communicates certain system faults. This information is displayed by connecting an LED test light to the test connection of the wiring harness near the ignition coil. The test connection is a single wire, either blue or blue/brown, leading to pin 4 of the knock sensor control unit.

To read the fault memory, connect an LED test light between the test connection and the battery positive (+) terminal, as shown in Fig. 4-7. When the ignition is turned ON, the LED should light, indicating that the control unit is responding. If it doesn't, check the connections and check for continuity of the wire from the test connector to terminal 4 of the knock sensor control unit connector. If there is continuity, the knock sensor control unit may be faulty.

Fig. 4-7:

Fig. 4-7. LED lest light connected to knock sensor control unit test connection (1), and test connection connected by jumper wire (2) to ground. LED test light shown is Volkswagen special tool no. US 1115.

Start the engine and briefly raise the engine speed to at least 3000 rpm. If the LED test light goes out, there is no fault formation stored, and the system is operating correctly. If it does not go OUT, or if it goes OUT and comes back ON, there is a fault in the system. Leave the engine idling and the LED test light connected, and connect a jumper wire from the test connector to ground, as shown in Fig. 4-7 above. Hold the connection for at least three seconds. The test light should flash in coded intervals. If the light does not flash, the control unit is faulty and should be replaced.

NOTE: Do not turn OFF the ignition during this procedure. Doing so will permanently erase the fault memory.

Two flashes per interval indicates a fault in either the circuit wiring, the knock sensor, or the knock sensor control unit. See Checking and Replacing Knock Sensor to continue troubleshooting.

Three flashes per interval indicates a problem with the vacuum connection to the knock sensor control unit. Check the vacuum hose for breaks and replace it if necessary. If there are no breaks, the control unit is faulty and should be replaced.

CIS-E Motronic (Engine Code 9A)
Cars with the CIS-E Motronic engine management system feature built-in electronic fault diagnosis which detects faults in the ignition system during normal operation. When activated, the control unit displays faults as a number code which corresponds to a particular component or function of the system which should be checked.

The service department should be equipped with an adequate analyzer which plugs into a special test connection in the car's wiring harness and 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.

This electronic check of the system is recommended by Volkswagen as the first step in any CIS-E Motronic troubleshooting. It is most certainly recommended for any car that is still protected by Volkswagen's extensive warranty coverage.