Knock sensor control limit, testing

If the fault message "Knock sensor - control limit reached" is recorded in the Diagnostic Trouble Code (DTC) memory the following tests must be carried out:

Test sequence

Connect the vehicle diagnostic, testing and information system VAS 5051. Refer to Vehicle diagnostic, testing and information system VAS 5051, connecting and selecting functions , and select the vehicle system "01 - Engine electronics" from the menu. When doing this the engine should be idling.

Fig 1: Diagnostic System VAS 5051: Display

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Display on VAS 5051:

Select the diagnosis function "08 - Read data block" from the menu -1-.

Fig 2: Diagnostic System VAS 5051: Display - Display Group And Key Pad

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Display on VAS 5051:

1 - Enter display group

(figures up to 255)

Using the keypad -2-, enter "020" to select Display group 020 and confirm entry with Q button.

Fig 3: Diagnostic System VAS 5051: Display - Display Fields

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Display on VAS 5051:

Check readouts for knock control in display zones -1- to -4-.

	Display zones
	1	2	3	4
Display group 020: Ignition - Knock control during driving
Display	xx.x ° KW	xx.x ° KW	xx.x ° KW	xx.x ° KW
Indicates	Ignition timing retardation by knock control: cylinder 1	Ignition timing retardation by knock control: cylinder 2	Ignition timing retardation by knock control: cylinder 3	Ignition timing retardation by knock control: cylinder 4
Specification	0 to 12 ° KW	0 to 12 ° KW	0 to 12 ° KW	0 to 12 ° KW
Note	Evaluation. Refer to Evaluating retardation of ignition timing

NOTE: The values indicated in display zones 1 to 4 show the actual amount of ignition retardation effected by the knock control at each cylinder. The retardation of ignition timing is indicated in degrees of crankshaft angle (°CA).

Press the ← button to exit from the function "08 - Read data block".

Evaluating retardation of ignition timing

Appears on display	Possible fault cause	Fault elimination
All cylinders greater than 12 °CA	Knock sensor defective	Check knock sensors. Refer to Knock sensors, testing
	Connector corroded
	Knock sensor incorrectly tightened	Loosen knock sensor and tighten to 20 Nm
	Ancillary components on engine loose	Tighten ancillary components
	Poor fuel quality	Change type of fuel (see owner's manual)
One cylinder differs significantly from the others	Connector corroded	Check knock sensors. Refer to Knock sensors, testing
	Engine damaged	Check compression pressures: Refer to 15 ENGINE - CYLINDER HEAD, VALVETRAIN for 1.8 LITER 4-CYL. 5V TURBO ENGINE MECHANICAL, ENGINE CODE(S): AMU, BEA 15 ENGINE - CYLINDER HEAD, VALVETRAIN for 1.8 LITER 4-CYL. 5V TURBO ENGINE MECHANICAL, ENGINE CODE(S): ATC, AWP 15 ENGINE - CYLINDER HEAD, VALVETRAIN for 3.2 LITER V6 4V ENGINE MECHANICAL, ENGINE CODE(S): BHE ; Removing and installing cylinder head; Checking compression pressure
	Ancillary components on engine loose	Tighten ancillary components