Note. Data exchange between individual control modules occurs via a bus system. The term "CAN-bus" refers to a system that transports and distributes data. The wire connections between the control modules, via which data is transferred, are referred to as data wires. Data is transferred to the connected control modules serially (one after the other) via these data wires.

Bus system, checking

The DTC table indicated that data exchange via the bus should be checked

Check to be sure the multi-pin connectors of the control modules are securely connected.

Requirements

VAS 5051/5052 tester connected and vehicle On Board Diagnostic (OBD) selected. Refer to «VAG 1551/1552 Scan Tool (ST), VAS 5051 Vehicle Diagnostic Testing and Information System or VAS 5052 Vehicle Diagnostic and Service System, connecting and selecting functions»(ref-276293-S20419373092008010300000) .
Ignition switched on.

Procedure

Scheme 29

Display on VAS 5051/5052

In selection -1-, press "00 - Check DTC Memory - complete system".

Note. The address word 00 initiates the automatic test sequence, i.e. it results in a DTC check on all OBD capable systems in the vehicle via rapid data transfer.

Wait until the next indication appears on display.

When a control module responds with its identification, the display indicates the number of stored errors or indicates "no malfunctions recognized".

If necessary, print out Screen content or On Board Diagnostic (OBD) protocol

Refer to Operating instructions for VAS 5051/5052 tester

If a malfunction involving "... databus" or "... no communication" is indicated

Check whether the correct control module for this vehicle is installed (part number and coding).

If the correct control modules are installed, check the CAN bus system.

Checking a "two-line bus system"

Three or more control modules are communicating across a "two-line bus system".

Analyze the DTCs stored in the memories of the control modules.

Note. This analysis will help you locate the cause of the line malfunction.

Scheme 30

Example 1

From the DTCs stored in the memories, you have determined that control module 1 is not communicating with control modules 2 and 3.

Control module	DTCs stored in DTC memories
1	Missing signal from control module 2 Missing signal from control module 3
2	Missing signal from control module 1
3	Missing signal from control module 1

Switch ignition off.
Disconnect the control modules connected across the bus wires and check the bus wires for an open circuit.

Refer to Wiring Diagrams, Troubleshooting & Component Locations

Replace control module 1 if no malfunctions can be found in the bus wires.

Scheme 31

Example 2

From the DTCs stored in the memories, you have determined that control module 2 is not communicating with control modules 1 and 3.

Control module	DTCs stored in DTC memories
1	Missing signal from control module 2
2	Missing signal from control module 1 Missing signal from control module 3
3	Missing signal from control module 2

Switch ignition off.
Disconnect the control modules connected across the bus wires and check the bus wires for an open circuit.

Refer to Wiring Diagrams, Troubleshooting & Component Locations

Replace control module 2 if no malfunctions can be found in the bus wires.

Example 3

Using the DTCs stored in the memories, you have determined that none of the control modules are sending or receiving signals.

Control module	DTCs stored in DTC memories
1	E.g. powertrain data-BUS malfunctioning
2	E.g. powertrain data-BUS malfunctioning
3	E.g. powertrain data-BUS malfunctioning

Switch ignition off.

Scheme 32

Disconnect the control modules connected across the bus wires and check for short circuits between the bus wires.

Refer to Wiring Diagrams, Troubleshooting & Component Locations

Scheme 33

Check the bus wires for short circuit to B+ or Ground (GND).

If a cause for the malfunction can not be determined, e.g. "powertrain data-BUS malfunctioning", check whether one of the control modules may be responsible for the DTC.

All control modules that use the CAN-bus are still disconnected. Ignition is switched off.

Connect one of the control modules.
Connect VAS 5051/5052 tester. Switch ignition on, and erase the DTC memory of the control module you just connected. End scan tool output using the "End Output" function 06.
Switch ignition off and then on.
Leave ignition on for 10 seconds. Then, read the DTC memory of the control module just connected.

If the DTC "powertrain data-BUS malfunctioning" is displayed, replace the control module just connected.
If the DTC "powertrain data-BUS malfunctioning" is not displayed, connect the next control module and repeat the procedure.

Display on VAS 5051/5052

Select diagnostic function "06 - End Output" in selection -1-.

Display on VAS 5051/5052

Switch off ignition and disconnect diagnostic connector after this indication is displayed.

Initiate On Board Diagnostic (OBD) of immobilizer. Refer to «Anti-theft immobilizer On Board Diagnostic (OBD), initiating»(ref-276293-S01612640412008010300000) .

Display on VAS 5051/5052

Select diagnostic function "08 - read measured value block" in selection -1-.

Scheme 34

Display on VAS 5051/5052

1 - Enter display group Max. input value = 255

Enter desired display group number in button field -2-. Refer to table --> «Read Measuring Value Block (function 08)»(ref-276293-S23411775532008010300000) .

Interpreting displayed information. Refer to Read Measuring Value Block (function 08) .

Scheme 35

Display on VAS 5051/5052

1 - Display group X

2 - Display field 1

Display field 2

Display field 3

Display field 4

Note. If no display follows, a display field is not assigned. To switch to a different display group, proceed as follows

Display group	VAS 5051/5052 tester
Higher	Press s button.
Lower	Press t button.

Press "08 - Erase DTC Memory" to end function <-- -button.

Read Measuring Value Block 20			>	<-- Indicated on display (example only)
AU	Z5	0W	10
				Immobilizer Identification No.1) 7th & 8th character
			Immobilizer Identification No.1) 5th & 6th character
		Immobilizer Identification No.1) 3rd & 4the character
	Immobilizer Identification No.1) 1st & 2nd character

1) Read function where applicable

Read Measuring Value Block 21			>	<-- Indicated on display (example only)
00	00	71
				Vacant
			Immobilizer Identification No.1) 13th & 14th character
		Immobilizer Identification No.1) 11th & 12th character
	Immobilizer Identification No.1) 9th & 10th character
AUZ5Z0W1000071

1) Read function where applicable

Read Measuring Value Block 22			>	<-- Indicated on display
X	X	X	X
				Number of adapted keys up to a max. of 8 keys
			Key condition OK 1 = yes, i.e. a structurally legitimate fixed transponder code could be read (regardless of whether it was authorized or not) 0 = no, i.e. no structurally legitimate fixed transponder code could be read
		Engine Control Module (ECM) responding 1 = yes (regardless of whether ECM is authorized or not) 0 = no, i.e. Engine Control Module (ECM) is in after-run1)
	Start procedure permitted 1 = yes 0 = no, i.e. ignition key is not adapted or incorrectly adapted or the Engine Control Module (ECM) is incorrectly adapted or malfunctioning

1) Depending on the Engine Control Module (ECM), the measuring value block registers position "0 = Engine Control Module not responding" for 10 to 30 seconds after engine and ignition are switched off, i.e. ECM is switched clear and there is no malfunction. Initiate On Board Diagnostic (OBD) again to be sure. Refer to Anti-theft immobilizer On Board Diagnostic (OBD), initiating .

Read Measuring Value Block 23			>	<-- Indicated on display
X	X	X	X
				Anti-theft immobilizer status 4: Customer service new; delivery condition of customer service (instrument cluster = replacement part) 5: Customer service locked; adaptation data programmed in customer service 6: Anti-theft immobilizer adapted, normal functioning condition 7: Key adaptation active; key adaptation via tester
			Fixed code authorized 1 = yes 0 = no, i.e. fixed transponder code of key is not authorized
		Key status (transponder) 1 = Transponder in key is locked, i.e. computational rule in key can no longer be overwritten. Key can no longer be adapted to a different anti-theft immobilizer system. 0 = Transponder in key is not locked, i.e. transponder has not yet been adapted to instrument cluster (new replacement part key).
	Variable code authorized 1 = yes 0 = no, i.e. variable code is not authorized (computational rule for variable code is not yet the same as that in the instrument cluster).

Read Measuring Value Block 24			>	<-- Indicated on display
XX	X		XX
				The transponder recognition locking time indicates how much time must pass before a transponder recognition is possible again. This lock is activated after an unauthorized key is detected 20 times in a row. 0 to 10 min1)
			Vacant
		The Engine Control Module (ECM) locking time indicates how much time must pass before an adaptation can be performed by the Engine Control Module again. If the 7-digit PIN is entered incorrectly three times while adapting channel 50, the control module is locked for 10 minutes 2). 0 to 255 min1)
	The instrument cluster locking time indicates how much time must pass before a login procedure can be performed again. If the 7-digit PIN is entered incorrectly three times during the login procedure (adaptation of vehicle key or used instrument cluster), the control module is locked for 10 minutes 1). 0 to 255 min1)

1) Read function where applicable.

2) This time is doubled after every third consecutive incorrect attempt, up to a maximum of 255 minutes.

	Read Measuring Value Block 25			>	<-- Indicated on display
	X
		CAN-communication to Engine Control Module (ECM)1) 1 = yes 0 = no, i.e. no CAN-communication between control module for anti-theft immobilizer and Engine Control Module (ECM) - Key adaptation not possible

1) Read function where applicable

Using the adaptation function, the following changes can be made and saved.

Perform adaptation of vehicle keys. Refer to «Adaptation of vehicle keys»(ref-276293-S18086613612008010300000)
Adaptation after replacing Engine Control Module (ECM). Refer to «Adaptation after replacing Engine Control Module (ECM)»(ref-276293-S01004715042008010300000) .
Adaptation after replacing instrument cluster. Refer to «Adaptation after replacing instrument cluster»(ref-276293-S00575498862008010300000) .

Data exchange between control modules, checking Audi TT 8N facelift