Diagnostic Instructions
DTC Descriptor
DTC U1814 00: Powertrain High Speed Communication Enable Circuit
Diagnostic Fault Information
Circuit
| Short to Ground
| Open/High Resistance
| Short to Voltage
| Signal Performance
|
Accessory Wakeup Serial Data
| U1814
| U0100
| --
| --
|
Circuit/System Description
The accessory voltage circuit is a positive voltage signal to wake up the from the body control module (BCM) to the engine control module (ECM) and the transmission control module (TCM). The signal is activated in 2 ways; any time the ignition switch is
in the ACC or RUN position, or anytime the body control module (BCM) determines that communication is needed from the powertrain. When the ignition switch is in the ACC or RUN position, the accessory voltage circuit input from the ignition switch to the BCM
is internally connected to the accessory voltage circuit output, and voltage is supplied to the modules. The BCM also supplies voltage to the accessory voltage circuit when it determines that communication is necessary with the powertrain and the ignition is
not in the ACC or RUN position such as during remote start.
Conditions for Running the DTC
| • | The system voltage is between 9-16 volts. |
| • | The vehicle power mode master requires serial data communication to occur. |
Conditions for Setting the DTC
The BCM senses a short to ground on the accessory voltage circuit from the BCM to the modules.
Action Taken When the DTC Sets
| • | The modules use a default value for the missing parameters until the next ignition cycle. |
| • | The modules is never signaled, therefore the specific subsystem(s) will not function. |
| • | The vehicle may not start. |
Conditions for Clearing the DTC
| • | A current DTC clears when the malfunction is no longer present. |
| • | A history DTC clears when the module ignition cycle counter reaches the reset threshold of 50, without a repeat of the malfunction. |
Diagnostic Aids
| • | Use the DMM MIN/MAX function to capture/locate intermittent conditions. |
| • | Short to ground may also set multiple no communication codes for GMLAN high speed modules. |
| • | Short to ground may also open the fuse feeding the ignition switch. |
Reference Information
Schematic Reference
Connector End View Reference
Master Electrical Component List
Electrical Information Reference
Circuit/System Testing
- With the ignition OFF, disconnect the harness connector at the ECM and TCM one at a time. After each disconnect, retest for current DTCs. DTC U1814 should remain current.
| ⇒ | If the DTC becomes history, replace the module disconnected before the DTC became history. |
- Ignition OFF, disconnect the harness connector at the BCM.
- Test for infinite resistance between the accessory voltage circuit from the BCM to the modules and ground.
| ⇒ | If less than infinite resistance, repair the voltage circuit for a short to ground. |
- If all tests normal, replace the BCM.
Repair Instructions
Perform the
Diagnostic Repair Verification
after completing the diagnostic procedure.
Control Module References
for module replacement, setup, and programming.
