Fuel System > Engine Control System > U0001 High Speed CAN Communication Bus off

General Description

Several control units are applied to electronically controlled vehicles. These units perform each control with informations from various sensors. Thus, sharing signal information from sensors is needed, so CAN communication type whose communication speed is high and insensitive to electrical noise by spark generation is adopted to controlling power-train(PCM, TCM,ESP PCM, ABS PCM)

As sharing signals of engine speed, APS, gear shifting, torque reduction in ESP and various modules, active control is performed.

DTC Description

Checking CAN communication, under detecting condition, if an error within the detecting condition is detected for more than 1.5 sec., PCM sets U0001. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycles.

DTC Detecting Condition

Item

Detecting Condition

Possible cause

DTC Strategy

•	Detects failures in communication between the PCM and another or modules in the vehicle which are on the CAN serial bus.

•

CAN BUS

•	CAN communication module component

EnableConditions

•	Engine Run Time ≥ 2sec.

•	Ignition Voltage ≥ 11V

Threshold value

•	CAN communicatin error

DiagnosisTime

•	Continuous

MIL On Condition

•	2 Driving Cycles

Specification

Communication Format	DIGITAL "0"		DIGITAL "1"( BUS IDLE )		CAN Communication Line Resistance
Communication Format	HIGH	LOW	HIGH	LOW	PCM	I/P Junction Box
CAN 2.0B	3.5V	1.5V	2.5V	2.5V	120Ω (20°C)	120Ω (20°C)

Schematic Diagram

Signal Wavefrom And Data

Monitoring CAN HIGH and LOW simultaneously is important in monitoring CAN communication waveform. When CAN HIGH signal rise to 3.5V and LOW signal drops to 1.5V - voltage difference between HIGH and LOW signal is 2V - at BUS IDLE state(DIGITAL "1") whose reference voltage is 2.5V, "0" is recognized. Besides, comparing HIGH and LOW signal if opposite waveform is detected with the reference voltage of 2.5V, Check if current cam signal transfers correctly.Continuous "0"signal above 6BIT means the occurence of error in CAN communication. 1BIT is easily distinguished as calculating the time when "SOF"(START OF FRAME) which notifies the start of frame occurs. Check if "0"signal above 6BIT is detected continuously when monitoring CAN communication waveform.

Terminal And Connector Inspection

1.	Electrical systems consist of a lot of harness and connectors, poor connection of terminals can cause various problems and damge of component.

Perform checking procedure as follows.

(1)	Check damage of harness and terminals : Check terminals for contact resistance, corrosion and deformation.

(2)

Check connecting condition of PCM and component connector : Check terminal seperation, damage of locking device and connecting condition between terminal and wiring.

Disconnect the pin which requires checking at male connector and insert it to the terminal at female connector for checking connecting condition. ( after checking, reconnect the pin at correct position. )

Is the problem found?

	▶ Repair the malfunctioning component and go to "Verification of Vehicle Repair".
	▶ Go to "Signal Circuit Inspection".

Signal Circuit Inspection

■ Check CAN BUS resistance in Data Link Connector

1.	Ignition "OFF"

2.	Measure the resistance between CAN-HIGH and CAN-LOW terminals of data link connector (Measurement "A")

3.	Disconnect PCM,Instrument Cluster, and ABS/ESC ECM connector.

Measure the resistance between CAN-HIGH and CAN-LOW terminals of data link connector (Measurement "B")

Specification :

PCM, Instrument Cluster and ABS/ESC ECM connected : 60 ± 3Ω (Measurement "A")

PCM, Instrument Cluster and ABS/ESC ECM disconnected : 120 ± 3Ω (Measurement "B")

Is CAN BUS resistance within the specification?

	▶ Go to "Check short to ground in CAN BUS" as follows.
	▶ Below 10Ω for both conditions(disconnected, connected) : Repair short between CAN BUS lines and go to "Verification of Vehicle Repair". ▶ 120Ω for both conditions(disconnected, connected) : Go to "4. Check CAN BUS continuity". ▶ Infinite Ω for both conditions(disconnected, connected) :Repair open in CAN communication circuit between DLC terminal and In-pannel junction box.

■ Check short to ground in CAN BUS

1.	Ignition "OFF"

2.	Disconnect PCM, Instrument Cluster and ABS/ESC ECM connector.

3.	Check resistance between CAN-HIGH terminal of Data Link Connector and chassis ground. (CAN HIGH line)

Check resistance between CAN-LOW terminal of Data Link Connector and chassis ground. (CAN LOW line)

Specification : Infinite

Is measured resistance within the specification?

	▶ Go to "Check short to battery in CAN BUS".
	▶ Repair short to ground in circuit and go to "Verification of Vehicle Repair".

■ Check short to battery in CAN BUS

1.	Ignition "OFF"

2.	Disconnect PCM, Instrument Cluster and ABS/ESC ECM connector.

3.	Ignition "ON"

4.	Measure the voltage between CAN-HIGH terminal of Data Link Connector and chassis ground. (CAN HIGH line)

Measure the voltage between CAN-LOW terminal of Data Link Connector and chassis ground. (CAN LOW line)

Specification : 0.0V~0.1V

Is measured resistance within the specification with both connector disconnected?

	▶ Go to"Check CAN BUS continuity" as follows.
	▶ Repair short to battery and go to "Verification of Vehicle Repair".

■ Check open in CAN BUS line

1.	Ignition "OFF"

2.	Disconnect PCM, Instrument Cluster and and ABS/ESC ECM connector.

3.	Check resistance between CAN-HIGH terminal of Data Link Connector and CAN-HIGH terminal of each module.(Measurement "A")

Check resistance between CAN-LOW terminal of Data Link Connector and CAN-LOW terminal of each module.

Specification : Below 1.0Ω

Is the measured resistance within the specification?

	▶ Go to "Component Inspection".
	▶ Repair open in CAN BUS line and go to "Verification of Vehicle Repair".

Component Inspection

■ Check CAN communication waveform generation

1.	Ignition "OFF"

2.	Connect each channel scope to CAN-HIGH terminal and CAN-LOW terminal.

3.	Ignition "ON" after disconnecting only PCM to CAN BUS.

4.	Ignition "ON" after disconnecting only ABS/ESC ECM to CAN BUS.

Ignition "ON" after disconnecting only Instrument Cluster to CAN BUS.

Specification : At Ignition "ON", the waveform same as "Signal Waveform & Data" of above signal waveform.

※ Different from "Signal Waveform & Data", if 1) both CAN HIGH and LOW signal are fixed at 2.5 V or 2) HIGH and LOW signal are fixed at 3.5 V and 1.5 V, respectively, it is due to communication error between modules.

Does correct waveform generate from each module?

	▶ Go to "Verification of Vehicle Repair".
	▶ Replace the module which generates poor communication waveform, and go to "Verification of Vehicle Repair".

Verification Of Vehicle Repair

After a repair, it is essential to verify that the fault has been corrected.

1.	Connect scantool and select "DTC" button.

2.	Press "DTC Status" button and confirm that "DTC Readiness Flag" indicates "Completed". If not, drive the vehicle within conditions noted in the freeze frame data or enable conditions

3.	Read "DTC Status" parameter

Is parameter displayed "History(Not Present) fault"?

	▶ System performing to specification at this time. Clear the DTC
	▶ Go to the applicable troubleshooting procedure.