Knock Sensor: Testing and Inspection
Knock Sensors, Checking
NOTE:
- For the Knock Sensors to function properly, it is important for tightening torque to be exactly 20 Nm.
- Use only gold-plated terminals when servicing terminals in harness connector of knock sensors.
Special tools and equipment
- VAG1551 scan tool (or VAG1552 mobile scan tool) with VAG1551/3B cable
- VAG1598/31 test box
- VAG1526 Multimeter (Fluke 83 or equivalent) or VAG1715 multimeter
- VAG1594 connector test kit
- Wiring diagram
Test requirement
- On Board Diagnostic (OBD) must have recognized a malfunction at one or both of the Knock Sensors (KS).
- Coolant temperature must be at least 85 °C, See display group 28, display field 3
Checking function
- Connect VAG1551 scan tool (VAG1552). Start engine and select the Engine Control Module (ECM) using address word Disconnecting scan tool and selecting ECM) Refer to " Scan Tool Testing/Scan Tool Connecting and Initial Checks " Testing and Inspection
Indicated on display:
Rapid data transfer HELP
Select function XX
- Press buttons -0- and -8- to select "Read measuring value block" function 08. Press -Q- button to confirm input.
Indicated on display:
Read measuring value block
Enter display group number XXX
- Press buttons -0-, -2- and -8- to select "Display group number 28". Press -Q- button to confirm input.
Indicated on display: (1 to 4 = display fields)
Read measuring value block 28 ->
1 2 3 4
NOTE: The test of the knock sensors must be performed during a road test since the knock sensor diagnostic is not active until above an engine speed of 2000 RPM and an engine load of more than 40%.
- Perform a road test and (have a 2nd person) observe the specified value for knock control on the display (display field 4).
Observe the safety precautions that apply to road tests
Display Group 28:
If specified value is obtained:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
Continuation:
If specified values are not obtained:
- Press -> button.
- Press buttons -0- and -6- to select "End Output" function 06. Press -Q- button to confirm input.
- Switch ignition off.
Knock Sensor (KS) 1 -G61-:
- Disconnect the 3-pin harness connector for knock sensor 1 (at cylinder block, on exhaust side) Knock Sensor (KS) 2 -G66-:
- Disconnect the 3-pin harness connector for knock sensor 2 (at cylinder block, on intake side)
- Measure resistance between terminals 1 + 2, 1 + 3, and 2 + 3 at connector for Knock Sensor (KS) 1 -G61-. Specification: Infinity Ohms
- Now measure resistance between terminals 1 + 2 at connector for Knock Sensor (KS) 2 -G66-, Specification: Infinity Ohms
If specified value is not obtained:
- Replace knock sensor (s) (-G61- and -G66-).
- Check DTC memory, repair any malfunctions and then erase DTC memory.
If specified value is obtained:
Checking wiring
- Connect VAG1598/31 test box to control module wiring harness. Engine Control Module (ECM) is not connected.
- Check wires between test box and 3-pin connector for open circuits according to wiring diagram.
G61:
Terminal 1 + socket 106
Terminal 2 + socket 99
Terminal 3 socket 108
Wire resistance: max: 1.5 Ohms
- Also check wires for short circuit to each other.
Specification: Infinity Ohms
- Now check wires between test box and 2-pin connector for open circuits according to wiring diagram.
G66:
Terminal 1 + socket 107
Terminal 2 + socket 99
Wire resistance: max: 1.5 Ohms
- Also check wires for short circuit to each other. Specification: Infinity Ohms
If no malfunctions are found in wires:
- Loosen the Knock Sensor (KS) and then retighten it to 20 Nm.
- Perform another road test and (have a 2nd person) observe the specified values for knock control on the display.
The following operating conditions must be obtained during road test:
- Coolant temperature must rise to above 85 °C.
- Once this temperature is reached, the following conditions
Idle
Partial throttle
Wide Open Throttle (WOT)\
Deceleration mode must be reached several times each.
- Engine speed must be increased to above 3500 RPM during Wide Open Throttle (WOT).
- Check control module's DTC memory again.
If complaint persists:
- Replace knock sensor (s) (-G61- and -G66-).
- Check DTC memory, repair any malfunctions and then erase DTC memory.
- Read readiness code. If DTC memory was erased or the Engine Control Module (ECM) was disconnected from the continuous B+ supply, the readiness code must be re-generated. Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Reading Readiness Code. Testing and Inspection Refer to Monitors, Trip and/or Drive Cycle (Readiness Codes)/Generating Readiness Code. Testing and Inspection