Knock Sensor System Diagnosis (Engines HT, RD, PL)

Fig. 2 Reading Fault Codes From Knock Sensor:

The knock sensor control unit 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 in the wiring harness near the ignition coil. The test connection has a single wire (either blue, or blue/brown) that leads to pin #4 of the knock sensor control unit.
To read the fault memory:
1. Connect an LED test light (US 1115 or equivalent) between the test connection and the positive (+) battery terminal.
2. When the ignition is turned ON, the test light should light, showing that the control unit is responding.
3. If the test light does not light, recheck the test connections, and the test connector wiring to the control unit.
4. Start the engine and briefly bring the engine speed above 3000 rpm.
a. If the test light goes out, the system is functioning normally and no faults were found.
b. If the light does not go out, or goes out and comes back on, there is a fault in the system.
Do not turn the ignition OFF. This will erase the fault memory.
5. With the engine idling and the test light still connected, connect a jumper wire from the test connector to ground for at least 3 seconds.
6. The test light should begin to flash in coded intervals.

Two flashes per interval:
Ignition system wiring
Faulty knock sensor
Faulty knock sensor control unit

Three flashes per interval:
Vacuum connection to the knock sensor control unit is leaking or blocked.
If vacuum supply is OK, control unit is faulty.

7. If the light does not flash, the control unit is faulty and should be replaced.