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 Wake Up Serial Data
| U1814
| U0100-U0299
| --
| --
|
Circuit/System Description
The accessory wake up serial data circuit is a positive voltage signal to wake up multiple control modules. 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 to the BCM is internally connected to the accessory wake up serial data circuit output, and voltage is supplied to the
modules. The BCM also supplies voltage to the accessory wake up serial data 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.
Modules activated by the accessory wakeup serial data circuit are as follows:
| • | Engine control module (ECM) |
| • | Transmission control module (TCM) |
| • | Transfer case control module (TCCM) (RPO NP8) |
| • | Serial data gateway module (SDGM) (RPO HP2) |
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 wake up serial data circuit.
Action Taken When the DTC Sets
| • | The modules use a default value for the missing parameters until the next ignition cycle. |
| • | The module(s) 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
Short to ground may also set multiple no communication codes for GMLAN high speed modules.
Reference Information
Schematic Reference
Connector End View Reference
Component Connector End Views
Description and Operation
Data Link Communications Description and Operation
Electrical Information Reference
Circuit/System Testing
- With the ignition OFF, disconnect the module harness connectors listed below one at a time. After each disconnect, retest for current DTCs. DTC U1814 should remain current.
| • | Engine control module (ECM) - X1 |
| • | Transmission control module (TCM) - X1 |
| • | Transfer case control module (TCCM) (RPO NP8) - X2 |
| • | Serial data gateway module (SDGM) (RPO HP2) - X2 |
| ⇒ | If the DTC becomes history, replace the module disconnected before the DTC became history. |
- Ignition OFF, disconnect the X4 harness connector at the BCM.
- Test for infinite resistance between the accessory wake up serial data circuit terminal 19 and ground.
| ⇒ | If less than the specified range, test the serial data circuit for a short to ground. |
- If the circuit 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
