Modules connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the modules. The modules have prerecorded information about what messages are needed to be exchanged on the serial data circuits, for each virtual network. The messages are supervised and also, some periodic messages are used by the receiver module as an availability indication of the transmitter module. Each message contains the identification number of the transmitter module.

DTC U1821 will set in the drive motor generator power inverter module when no communication is established with the accessory DC power control module on the PTLAN serial data bus.

A supervised periodic message that includes the transmitter module availability has not been received.

The modules is never signaled, therefore the specific subsystems will not function.

Different DTCs may set in different modules along with this DTC depending on where the fault occurs and the vehicle operating conditions when the fault occurs.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Data Link Communications Description and Operation

Electrical Information Reference

Special Tools

EL-48900 HEV Safety Kit

Verify DTC U182A is not set in the serial data gateway module (SDGM).

Danger: Always perform the High Voltage Disabling procedure prior to servicing any High Voltage component or connection. Personal Protection Equipment (PPE) and proper procedures must be followed.

The High Voltage Disabling procedure will perform the following tasks:

•	Identify how to disable high voltage.

•	Identify how to test for the presence of high voltage.

•	Identify condition under which high voltage is always present and personal protection equipment (PPE) and proper procedures must be followed.

Failure to follow the procedures exactly as written may result in serious injury or death.
1. Ignition OFF, disable the high voltage at the drive motor generator battery. Refer to High Voltage Disabling.
2. Ignition OFF, disconnect harness connector X4 of the accessory DC power control module.
3. Test for less than 1.0 ohm between the accessory DC power control module connector terminal and ground.

⇒	If greater than the specified value, test the ground circuit for an open/high resistance.

4. Ignition ON, disconnect harness connector X3 of the accessory DC power control module.
5. Verify that a test lamp illuminates between the accessory DC power control module connector terminal A and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

6. Ignition OFF, disconnect harness connector X1 of the accessory DC power control module and the drive motor generator power inverter module.
7. Test for less than 1.0 ohm at the accessory DC power control module connector and drive motor generator power inverter module connector between the following connector serial data terminals.

•	Accessory DC power control module terminal 1 and drive motor generator power inverter module terminal 24

•	Accessory DC power control module terminal 2 and drive motor generator power inverter module terminal 25

⇒	If greater than the specified value, test the serial data circuits for an open/high resistance.

8. Test for infinte resistance between the accessory DC power control module terminal 2 and accessory DC power control module terminal 1.

⇒	If less than the specified value, test the serial data circuits for a short between the circuits.

9. If all circuits test normal, replace the accessory DC power control module.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.