DTC P0856 3.6L (LY7)
Circuit Description
The electronic brake control module (EBCM) and the engine control module (ECM) simultaneously control the traction control. The ECM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning OFF fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.
When certain ECM DTCs are set, the ECM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0856 Traction Control System Input Signal
Conditions for Running the DTC
| • | Control Area Network Bus has been initialized and ready. |
| • | The ignition is on for more than 3 seconds. |
| • | The ignition 1 voltage is between 10.5-18 volts. |
| • | Bus Communication runs OK. |
| • | DTC P0856 runs continuously once the above conditions are met for more than 1 second. |
Conditions for Setting the DTC
| • | The traction information which the ECM sends to the EBCM is temporarily stopped or the content of the information is invalid. |
| • | The above conditions exist for up to 4 seconds. |
Action Taken when the DTC Sets
| • | The EBCM disables the EDC/TCS during the ignition cycle. |
| • | The Traction Off indicator turns ON. |
| • | The ABS remains functional. |
Conditions for Clearing the DTC
| • | The condition for setting the DTC removes and use the scan tool Clear DTCs function to remove the DTCs. The EBCM automatically clears the history DTC when a current DTC is not detected in 100 consecutive drive cycles. |
| • | The ECM automatically clears the history DTC when a current DTC is not detected in 40 consecutive warm-up cycles. |
Diagnostic Aids
The following conditions can cause this concern:
| • | A communication signal frequency problem |
| • | The EBCM is not receiving information from the ECM. |
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||
2 |
Does the scan display less than the specified value? | 100% | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | ||||
3 |
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition. | -- | Go to Step 9 | Go to Step 4 | ||||
4 |
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 5 | ||||
5 | Inspect for poor connections at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 6 | ||||
6 | Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 7 | ||||
7 | Replace the EBCM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 9 | -- | ||||
8 | Replace the EBCM Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 9 | -- | ||||
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
DTC P0856 4.6 (LH2)
Circuit Description
The electronic brake control module (EBCM) and the engine control module (ECM) simultaneously control the traction control. The ECM reduces the amount of torque supplied to the drive wheels by retarding spark timing and selectively turning OFF fuel injectors. The EBCM actively applies the brakes to the front wheels in order to reduce torque.
When certain ECM DTCs are set, the ECM will not be able to perform the torque reduction portion of traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0856 Traction Control System Input Signal
Conditions for Running the DTC
| • | Torque reduction signal diagnosis has activated. |
| • | Engine has been running. |
| • | Power mode has been activated. |
| • | Traction Control System sends data information to GM Local Area Network. |
| • | DTC P0856 runs continuously once the above conditions are met. |
Conditions for Setting the DTC
The traction information which the ECM sends to the EBCM is temporarily stopped or the content of the information is invalid.
Action Taken when the DTC Sets
| • | The EBCM disables the EDC/TCS during the ignition cycle. |
| • | The Traction Off indicator turns ON. |
| • | The ABS remains functional. |
| • | DTC P0856 is a type C DTC. |
Conditions for Clearing the DTC
DTC P0856 is a type C DTC.
Diagnostic Aids
The following conditions can cause this concern:
| • | A communication signal frequency problem. |
| • | The EBCM is not receiving information from the ECM. |
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | |||||
2 |
Does the scan display less than the specified value? | 100% | Go to Testing for Intermittent Conditions and Poor Connections | Go to Step 3 | ||||
3 |
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 4 | ||||
4 |
Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 5 | ||||
5 | Inspect for poor connections at the harness connector of the ECM. Refer to Testing for Intermittent Conditions and Poor Connections . | -- | Go to Step 9 | Go to Step 6 | ||||
6 | Inspect for poor connections at the harness connector of the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections . Did you find and correct the condition? | -- | Go to Step 9 | Go to Step 6 | ||||
7 | Replace the ECM. Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 9 | -- | ||||
8 | Replace the EBCM Refer to Control Module References for replacement, setup and programming. Did you complete the replacement? | -- | Go to Step 9 | -- | ||||
9 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
