Knock recognition control limit, checking

If a DTC relating to "knock recognition control limit reached" is made, perform the following checks:

Work sequence

Connect vehicle diagnostic, testing and information system VAS 5051. Refer to VAS 5051 vehicle diagnostic, testing and information system, connecting and selecting functions and select vehicle system "01 -Engine electronics" in selection. Engine must be run at idle.

Fig 1: Diagnostic System VAS 5051: Display

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Display on VAS 5051:

Under -1- select diagnostic function "08 - Read measured value block".

Fig 2: Diagnostic System VAS 5051: Display

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Display on VAS 5051:

1 - Enter display group

Enter "020" for "display group number 020" in zone -2- and confirm entry by pressing -Q- button.

Fig 3: Diagnostic System VAS 5051: Display

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Display on VAS 5051:

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

	Display zones
	1	2	3	4
Display group 020: Ignition knock recognition control while driving
Display	xx.x ° KW	xx.x ° KW	xx.x ° KW	xx.x ° KW
Display	Ignition timing retardation by knock recognition control, cylinder 1	Ignition timing retardation by knock recognition control, cylinder 2	Ignition timing retardation by knock recognition control, cylinder 3	Ignition timing retardation by knock recognition control, cylinder 4
Specified value	0...12 ° crankshaft	0...12 ° crankshaft	0...12 ° crankshaft	0...12 ° crankshaft
	Evaluation. Refer to Evaluation ignition angle retardation

NOTE: The numbers displayed in display zones 1 to 4 represent the actual ignition timing retardation due to the knock control of the individual cylinders. The ignition angle retardation is carried out late in ° KW (crankshaft degree).

Exit function "08 - Read measured value block" by pressing ← button.

Evaluation ignition angle retardation

Indicated on display	Possible cause	Corrective Action
All cylinders greater than 12 ° KW	Knock sensor malfunction	Check knock sensor. Refer to Knock sensors, checking
	Connector corroded	Check knock sensor. Refer to Knock sensors, checking
	Knock sensor incorrectly tightened	Loosen knock sensor and retighten to 20 Nm.
	Loose components on engine	Secure components
	Poor fuel quality	Changing fuel grade (see operating instructions)
One cylinder deviates significantly from the others	Connector corroded	Check knock sensor. Refer to Knock sensors, checking
	Engine malfunction	Check compression: Refer to 15 - ENGINE - CYLINDER HEAD, VALVETRAIN , Compression pressure, checking
	Loose components on engine	Secure components