The engine control module (ECM), electronic brake control module (EBCM) if applicable, fuel injector control module (FICM) if applicable, glow plug control module (GPCM) if applicable, and transmission control module (TCM) if applicable, communicate via a controller area network (CAN) serial data bus. Modules connected to the CAN serial data circuits monitor communications. During normal vehicle operation, information and commands are exchanged among modules. A no communication condition may result from a short to voltage, short to ground, an open in the CAN High or Low circuits, or short between the CAN high and low circuits.
• | The ignition is ON and engine running. |
• | The module supply voltage is in the normal operating range of 9-16 volts. |
A no communication condition is detected on CAN serial data circuits.
• | The module uses a default value for the missing parameter. |
• | The malfunction indicator lamp (MIL) illumination depends on DTC type. For a detailed description about DTCs types refer to Diagnostic Trouble Code (DTC) Types in Engine Controls - 6.6L (LB7). For information about DTC type definitions, refer to Diagnostic Trouble Code (DTC) Type Definitions in Engine Controls - 6.6L (LB7). |
MIL or DTC clearing depends on DTC type. For a detailed description about DTCs types refer to Diagnostic Trouble Code (DTC) Types in Engine Controls - 6.6L (LLY). For information about DTC type definitions refer to Diagnostic Trouble Code (DTC) Type Definitions in Engine Controls - 6.6L (LLY).
• | DTC Type C |
• | A current DTC and MIL clear when the malfunction is no longer present. |
• | A history DTC clears when the module ignition cycle counter reaches the reset threshold, without a repeat of the malfunction. |
The modules communicating on the CAN serial data circuits are wired parallel to each other until the respective circuits are spliced together outside of the ECM. An open in the CAN circuits for one module will not affect other modules. A short to ground or short to voltage affects all modules no matter where the failure occurs.
The number below refers to the step number on the diagnostic table.
Step | Action | Values | Yes | No |
---|---|---|---|---|
Schematic Reference: Data Link Connector Schematics Connector End View Reference: Data Link Communications Connector End Views | ||||
1 |
Does the DTC fail this ignition? | -- | Go to Step 2 | Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems |
2 |
Important: Turn ON the ignition, with the engine OFF, when testing for a short to voltage. Use DMM MIN/MAX function to compare intermittent conditions.
Refer to Circuit Testing in Wiring Systems Did you find and correct the condition? | -- | Go to Step 18 | Go to Step 3 |
Important: If the vehicle is not equipped with an FICM, answer YES to this step.
Does the frequency measure more than the specified value? | 35,000 Hz | Go to Step 4 | Go to Step 8 | |
4 |
Important: If the vehicle is not equipped with a TCM, answer YES to this step.
Does the frequency measure more than the specified value? | 35,000 Hz | Go to Step 5 | Go to Step 9 |
5 |
Important: If the vehicle is not equipped with an EBCM, answer YES to this step.
Does the frequency measure more than the specified value? | 35,000 Hz | Go to Step 6 | Go to Step 10 |
6 |
Important: If the vehicle is not equipped with an GPCM, answer YES to this step.
Does the frequency measure more than the specified value? | 35,000 Hz | Go to Step 7 | Go to Step 11 |
7 | Inspect for an intermittent or poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 17 | Go to Step 12 |
8 | Inspect for an intermittent or poor connection at the FICM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you fine and correct the condition? | -- | Go to Step 17 | Go to Step 13 |
9 | Inspect for an intermittent or poor connection at the TCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you fine and correct the condition? | -- | Go to Step 17 | Go to Step 14 |
10 | Inspect for an intermittent or poor connection at the EBCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you fine and correct the condition? | -- | Go to Step 17 | Go to Step 15 |
11 | Inspect for an intermittent or poor connection at the GPCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you fine and correct the condition? | -- | Go to Step 17 | Go to Step 16 |
12 |
Important: Perform the module setup procedure, if required. Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 6.6L (LB7). Did you complete the replacement? | -- | Go to Step 17 | -- |
13 |
Important: Perform the module setup procedure, if required. Replace the FICM. Refer to Fuel Injector Control Module Replacement in Engine Controls - 6.6L (LB7). Did you complete the replacement? | -- | Go to Step 17 | -- |
14 |
Important: Perform the module setup procedure, if required. Replace the TCM. Refer to Transmission Control Module Replacement in Automatic Transmission - Allison. Did you complete the replacement? | -- | Go to Step 17 | -- |
15 |
Important: Perform the module setup procedure, if required. Replace the EBCM. Refer to Electronic Brake Control Module Replacement in Air Antilock Brakes or Electronic Brake Control Module Replacement in Antilock Brakes. Did you complete the replacement? | -- | Go to Step 17 | -- |
16 |
Important: Perform the module setup procedure, if required. Replace the GPCM. Refer to Glow Plug Controller Replacement in Engine Controls. Did you complete the replacement? | -- | Go to Step 17 | -- |
17 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 15 |
18 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK |