U029D

DTC U029D Lost Communication With NOx Sensor 1 Or NOx Sensor CAN Communication

Circuit Description

The DEF control module, NOx sensors 1 control module and NOx sensor 2 control module communicate control and diagnostic information via the 250 kbps transmission speed controller area network (CAN) circuit. The twisted pair wire is terminated with two 120 ohms resistors, one is internal to the DEF control module and the other is wrapped to the chassis wire harness with tape. The DEF control module monitors CAN operational status by receiving constant flow of messages from the NOx sensor control modules. If the DEF control module fails to receive constant messages from the NOx sensor 1 control module, this DTC will set. If the DEF control module sets CAN bus Off status, this DTC will also set.

Condition for Running the DTC

- The battery voltage is between 10 to 16 volts.
- The ignition switch is ON.

Condition for Setting the DTC

Either of following condition is met:
- The DEF control module detects the CAN communication bus OFF status longer than 3 seconds.
- The DEF control module detects that the CAN bus messages from the NOx sensor 1 control module are not being received longer than 7 seconds.

Action Taken When the DTC Sets

- The DEF control module requests the ECM to illuminate the MIL. Refer to DTC Type Definitions for Action Taken When the DTC Sets - Type A.
- The DEF control module and the ECM apply defaulted warning actions. Refer to Default Action and Fail- Safe List.

Conditions for Clearing the DTC

- Refer to DTC Type Definitions for Conditions for Clearing the DTC - Type A or Type B.

Diagnostic Aids

- If an intermittent condition is suspected, refer to Intermittent Conditions in this section.
- Parallel resistance of the 120& resistor in the DEF control module and the CAN terminating resistor should be 60 ohms.

Test Description

The number below refers to the step number on the Circuit/ System Testing.
3. If only DTC U029E is being present, inspect the NOx sensor 2 control module harness connector for corrosion or incorrect connections first.
4. If only DTC U029D is being present, inspect the NOx sensor 1 control module harness connector for corrosion or incorrect connections first.
5. If DTC U029E is not set, inspect the NOx sensor 1 control module address switch ground circuit. The NOx sensor control module recognizes sensor 1 by pulling the circuit to ground.

Circuit / System Testing DTC P029D