Description

Communication on the CAN bus fails due to CAN ´bus off´ conditions.

A CAN ´bus off´ condition occurs if the error counter of a CAN controller exceeds 255.

The CAN controller is disconnected from the CAN bus using an internal logic function and does no longer participate in the bus activities. The control unit that belongs to the CAN controller can no longer receive or send CAN messages.

Effects on the driving operation

Driving is not possible or restricted.

Transmission shifts sporadically to neutral.

Lighting of the gear range selector becomes dark.

Possible causes

Short-circuit between CAN-H and CAN-L or short-circuit of one or both lines to ground or to supply voltage.

Another CAN bus node sends with an incorrect bit rate (250kbit/s are expected).

Other bus node is defective.

Defect CAN transceiver in the gear range selector controller

Defect CAN transceiver in E330.

Connection of the CAN gear selector switch

The jumpers on the transmission control unit (D13 to D17) and on the CAN gear range selector (6 to 7) activate the integrated CAN terminating resistors since the transmission control unit and the CAN gear range selector are usually the only CAN bus nodes at CAN2. The CAN bus must always be wired with the terminating resistors on both sides.

Connector pin assignment of transmission control unit

Pin	Stecker A	Stecker B	Stecker C	Stecker D
1	SHIELD	EK	FLEXI-1	-BATT
2	TIM+	DK	---	IGN
3	TIM-	SK	FLEXI-3	FLEXI-11
4	N1+	RBK	FLEXI-4	K-LINE
5	N1-	TB	FLEXI-5	CAN1-H
6	N2+	---	FLEXI-6	CAN1-H
7	N2-	RBG	FLEXI-7	CAN-SHLD
8	N3+	PB	FLEXI-8	CAN1-L
9	N3-	WR	FLEXI-9	CAN1-L
10	---	WP	FLEXI-10	CAN2-H
11	---	---	FLEXO-2H	CAN2-H
12	EKM	FLEXI-12	FLEXO-4H	CAN2-L
13	DKM	S-GND	FLEXO-3H	CAN2-L
14	SKM	OIL-LVL	FLEXO-5L	CAN1-R
15	PBM	T-SUMP	---	---
16	TBM	---	---	FLEXO-1L
17	RBKM	T-CONV	---	CAN2-R
18	MVM-GND	MV-GND	---	+BATT

Connector pin assignment of CAN gear selector switch

Pin	Name	Pin	Name	Pin	Name
1	IGN	6	CAN-H	11	FLEXI-4
2	-BATT	7	CAN-R	12	FLEXI-5
3	CAN-L	8	FLEXI-1	13	FLEXI-6
4	CAN-L	9	FLEXI-2	14	FLEXO-1H
5	CAN-H	10	FLEXI-3

Place of action

No description available.

Instruction

Check the cabling (cable break, loose contact, high contact resistance).

Measure between CAN-H and CAN-L: the resistance must be approx. 60 ohms – install / repair bus terminating resistor if necessary.

Measure between CAN-H and CAN-L (the resistance must be approx. 60 ohms) – check / repair cabling if necessary.

Measure CAN-H and CAN-L to ground: the resistance must be significantly larger than 1kohm – check / repair cabling if necessary.

Measure CAN-H and CAN-L to supply voltage: the resistance must be significantly larger than 1kohm – check / repair cabling if necessary.

Check whether correct dataset in control unit (correct CAN protocol); if not, replace dataset,

disconnect the other bus nodes one after the other and check whether this eliminates the fault – replace defective control unit or contact manufacturer.

Disconnect and check one bus node after the other and see whether the fault is thus eliminated – replace the defective / faulted control unit. Replace control unit of gear range selector.

Setting conditions of the event

No description available.

Test conditions of the event

No description available.

Troubleshooting

• Measure resistance between CAN-H and CAN-L. The nominal value is 60 Ω.
• Measure resistance between CAN-H and ground. The resistance must lie well above 1 kΩ.
• Measure resistance between CAN-L and ground. The resistance must lie well above 1 kΩ.
• Measure the resistance between CAN-H and supply voltage. The resistance must lie well above 1 kΩ.
• Measure the resistance between CAN-L and supply voltage. The resistance must lie well above 1 kΩ.
• Check whether the correct dataset is active in the transmission control unit.
• Check whether the correct CAN protocol is active.
• Disconnect the other control units from the CAN bus one after the other and check whether this eliminates the fault.
• Replace CAN gear range selector.

Final function check

If the defective component cannot be clearly identified, you should try to reproduce the fault:

• Reinstall the component in the vehicle.
• Test the function.

After the fault has been eliminated, the following steps have to be carried out:

• Conduct a test drive with function check.
• Read out the fault memory.
• Check the transmission for leaks.
• Perform a final visual inspection.

These steps are necessary to ensure the entire vehicle functions.

See also:

		Aftersales service index