C1242

DTC C0857 or C1242

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions Diagnostic Procedure Instructionsprovides an overview of each diagnostic category.

DTC Descriptors
DTC C0857 00
- Ignition Accessory Switch Circuit Low Voltage

DTC C1242 00
- Ignition Accessory Switch Circuit Low Voltage

Diagnostic Fault Information






Circuit/System Description

The hybrid powertrain control module 2 sends the accessory power mode status in a serial data message to the electronic brake control module (EBCM). The hybrid powertrain control module 2 also powers up the accessory circuit to the EBCM when the propulsion system is active, after the vehicle crank mode.

Conditions for Running the DTC

* Vehicle power mode is propulsion system active
* EBCM is awake
* System voltage greater than 9 V

Conditions for Setting the DTC

RUN/Crank input is active, and 500 ms after the RUN/Crank input transitions high, a voltage below 5 V is detected for at least 5 seconds.

Action Taken When the DTC Sets

No action is taken.

Conditions for Clearing the DTC

* The current DTC will clear when the malfunction is no longer present.
* A history DTC clears when the module ignition cycle counter reaches the reset threshold of 40, without a repeat of the malfunction.

Diagnostic Aids

A short to voltage in the ACC control circuit will keep the vehicle bus awake, which can drain the vehicle's battery.

Reference Information
Schematic Reference

* Body Control System Schematics [1][2]Body Control Systems
* Power Distribution Schematics Power Distribution Schematics

Connector End View Reference

Component Connector End Views Hybrid/EV Battery Pack X1 A4
Description and Operation

Power Mode Description and Operation Power Mode
Electrical Information Reference

* Circuit Testing Circuit Testing
* Connector Repairs Connector Repairs
* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections
* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Control Module Referencesfor scan tool information

Circuit/System Testing

1. Disconnect the harness connector at the K17 electronic brake control module.
2. Ignition OFF, test for B+ between the ignition circuit terminal 12and ground.

• If B+, test the ignition circuit for a short to voltage. If the circuit tests normal, replace the K114B hybrid powertrain control module 2.

3. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 12 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the K114B hybrid powertrain control module 2.

4. If all circuits test normal, replace the K17 electronic brake control module.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

Control Module References Control Module Referencesfor the appropriate control module replacement, programming and setup