DTC 4-3-3 - Rear Knock Sensor Signal
WARNING: This page is about a different car, the 1996 Volvo 850. However, it is still accessible from the selected car via links, so may be relevant.
See DTC 1-4-3 - FRONT KNOCK SENSOR SIGNAL & DTC 4-3-3 - REAR KNOCK SENSOR SIGNAL circuit test.