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| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
B+ | U1850* | U1850* | -- | -- |
Ignition | U1850* | U1850* | -- | -- |
Accessory Wake Up Serial Data 2 | P06E4* | U1850* | -- | -- |
High Speed GMLAN Serial Data (+) | U0073, 1 | U0073, U1850* | U0073, 1 | -- |
High Speed GMLAN Serial Data (-) | U0073, 1 | U0073, U1850* | U0073, 1 | -- |
Ground | -- | U1850* | -- | -- |
* Other modules/DTCs may set with this fault. 1. Scan Tool Does Not Communicate With High-Speed GMLAN Device. | ||||
Control modules connected to the serial data circuits monitor for serial data communications during normal vehicle operation. Operating information and commands are exchanged among the control modules. The control 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.
| • | The system voltage is at least 10 V. |
| • | The vehicle power mode master requires serial data communication to occur from this specific control module. |
A supervised periodic message that includes the transmitter module availability has not been received.
The DTC U1850 is a type B DTC.
The DTC U1850 is a type B DTC.
| • | Sometimes, while diagnosing a specific customer concern or after a repair, you may notice a history U-code present. However, there is no associated "current" or "active" status. Loss-of- communication U-codes such as these can set for a variety of reasons. Many times, they are transparent to the vehicle operator and technician, and/or have no associated symptoms. Eventually, they will erase themselves automatically after a number of fault-free ignition cycles. This condition would most likely be attributed to one of these scenarios: |
| - | A control module on the data communication circuit was disconnected while the communication circuit is awake. |
