For 1990-2009 cars

### 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 Wake Up Communication Circuit

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Powertrain Serial Data Communication Enable | U1814, 1 | U0100-U0299 | -- | --
1. Vehicle will not start.

### Circuit/System Description

The body control module (BCM) activates the serial data communication enable circuit when the ignition key is in ACC, ON or START. The serial data communication enable circuit wakes up the engine control module (ECM) for serial data bus communication.

### 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 serial data communication enable circuit.

### Action Taken When the DTC Sets

• | The output command is turned off while the malfunction is present.

• | 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 will not start while the circuit is shorted to ground.

### 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 will also set multiple history no communication codes for GMLAN high speed modules.

### Reference Information

#### Schematic Reference

Data Communication Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Data Link Communications Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the K20 ECM.
2. Retest for current DTCs. DTC U1814 should remain current.

⇒ | If the DTC becomes history, replace the K20 ECM.

3. Ignition OFF, disconnect the X 4 harness connector at the K9 BCM.
4. Test for infinite resistance between the serial data communication enable circuit terminal 22 and ground.

⇒ | If less than infinite resistance, repair the enable circuit for a short to ground.

5. If all circuits tests normal, replace the K9 BCM.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for module replacement, setup, and programming