U0020 - CONTROLLER AREA NETWORK (CAN) DATA BUS: LOW-SPEED BUS - PERFORMANCE PROBLEM

Some control modules are connected to the CAN bus (Control Area Network). This bus maintains constant information on vehicle operating data and commands. These modules contain pre-recorded information related to the messages that need to be exchanged between the serial data circuits.

On the other hand, these messages are monitored, and also some periodic messages are used from the receiver module. These act as availability indicators of the transmitter module. Typically, the supervision timeout is 250 ms, and each of them includes a transmitter module ID.

The U0020 OBDII fault code must be set when fewer modules are detected on the bus before they can learn the IDs of other controllers. This code indicates that a supervised periodic message, including the availability of the transmitter module, has not been received.

• Check Engine light ON.
• Trouble getting the vehicle to start.
• Unexpectedly the engine shuts down.

The Diagnostic code U0020 OBD2 is set by one more of the following reasons:

• The electrical connections of the Control Area Network may be damaged.
• Possibly a low voltage condition exists due to battery deficiencies.
• A controller may be faulty.

Troubleshoot DTC U0020 OBDII code by considering the following suggestions:

• See TSBs.
• Use a scanner, check if other DTCs are set that are related to the CAN bus communication failures. If you detect one of these codes, perform the corresponding diagnosis.
• Verify that the controller related to the fault and its ground circuit is not faulty. Check that the resistance is as indicated by the manufacturer.
• Perform voltage tests on the modules related to this DTC. If a short or high resistance is found, it is necessary to check the integrity of the connections and the controller. Fix if necessary.