Service Information

Captiva

DTC U1814

Diagnostic Instructions

•	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.

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	--	--

The accessory wakeup serial data circuit is a positive voltage signal to wake up 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 to the BCM is internally connected to the accessory wakeup serial data circuit output, and voltage is supplied to the modules. The BCM also supplies voltage to the accessory wakeup 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.

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 wakeup 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 signalled, 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.

Reference Information

Schematic Reference

•	Body Control System Schematics

•	Data Communication Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

•	Circuit Testing

•	Connector Repairs

•	Testing for Intermittent Conditions and Poor Connections

•	Wiring Repairs

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 wakeup serial data circuit and ground.

⇒	If less than infinite resistance, repair the serial data 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