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Trace a CAN fault from the application and RTE down through the relevant Basic Software (BSW) modules to the CAN interface and driver. For a UDS request carried over CAN, the diagnostic path typically involves Can → CanIf → PduR → CanTp → PduR → Dcm; ordinary application signals more commonly involve COM and the RTE. The exact configuration varies by ECU, so use the path to identify where to check—not as a universal wiring diagram.
How AUTOSAR layers help isolate a CAN problem
AUTOSAR separates application behavior from communication services and hardware access. The application layer contains software components (SWCs); the Runtime Environment (RTE) connects their ports to other components and ECU services. Below the RTE, the service layer, ECU abstraction layer, and microcontroller abstraction layer are commonly grouped as Basic Software (BSW).
This division gives you a practical fault-isolation direction: start where the symptom appears, then follow the configured communication path downward. The RTE and upper BSW interfaces are intended to reduce hardware dependence; the microcontroller abstraction and CAN drivers are tied more directly to the ECU hardware. The CAN communication stack is designed to keep application code from having to manage CAN protocol and message details itself.
What each boundary tells you
- Application SWC: Is the software component producing or consuming the expected data or requesting the expected diagnostic operation?
- RTE: Are the component ports and generated interfaces mapped as intended? For signal communication, check the sender/receiver relationship; for service calls, check the client/server mapping.
- BSW communication services: Are signals and I-PDUs configured, routed, transported, and interpreted correctly?
- CAN interface and driver: Is the configured CAN communication reaching the controller and physical network as expected?
Which AUTOSAR modules handle CAN signals and UDS?
There is not one module that handles every CAN problem. COM manages application I-PDUs and signals; PduR routes I-PDUs; CanTp transports segmented diagnostic messages; Dcm handles diagnostic communication and services; and Dem manages diagnostic events and trouble-code data. CanIf provides a uniform interface between upper layers and the CAN hardware.
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| Module | Role in diagnosis | Useful first check |
|---|---|---|
| RTE | Connects SWC ports to other components or ECU services. | Port configuration, sender/receiver or client/server mapping, and generated RTE interfaces. |
| COM | Handles application signals and I-PDUs. | Signal and I-PDU configuration, including whether the expected data is packed and handled as configured. |
| PduR | Forwards I-PDUs between configured modules, including CanIf, CanTp, Dcm, and COM. | Routing paths, direction, and source/destination configuration. |
| CanTp | Implements ISO 15765-2 transport, including segmentation and flow control for diagnostic messages. | Transport configuration and whether multi-frame transfers complete correctly. |
| Dcm | Processes diagnostic communication and services, including UDS requests. | Session, timing, service permissions, and response handling. |
| Dem | Manages diagnostic events, DTCs, and associated freeze-frame or extended data. | Event qualification, DTC status, stored data, and persistence. |
| CanIf | Provides the uniform interface between upper layers and CAN hardware. | Configured CAN interface behavior and its relationship to the controller. |
| CAN driver (Can) | Communicates with the CAN controller through the hardware-dependent driver layer. | Controller and driver configuration, then frame-level evidence from the ECU or network. |
Trace a UDS request through the CAN stack
For a diagnostic request received over CAN, the usual conceptual route is Can → CanIf → PduR → CanTp → PduR → Dcm. The response travels back through the configured stack toward the CAN interface. PduR is a forwarding layer: it routes the I-PDU rather than interpreting or modifying its diagnostic payload. Actual route details depend on the ECU’s configuration.
- Can and CanIf: Establish whether a CAN frame is reaching the controller and being made available through the CAN interface.
- PduR: Verify that the configured receive route forwards the relevant I-PDU to CanTp. PduR also routes traffic between configured destinations; it does not replace the functions of the modules at either end.
- CanTp: Check ISO 15765-2 transport behavior, especially segmentation and flow control when a message spans multiple frames.
- PduR to Dcm: Confirm that the reassembled diagnostic message is routed to Dcm.
- Dcm: Check whether the request is valid for the active diagnostic session, timing, and configured service permissions, and whether the expected response is generated.
EE Times describes Dcm as having three functional blocks: Diagnostic Session Layer (DSL), Diagnostic Service Dispatcher (DSD), and Diagnostic Service Processing (DSP). That 2010 explanation is useful for understanding the conceptual division, but its AUTOSAR 3.1-era statements about service support should not be treated as descriptions of current releases.
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When COM is involved instead
For an application signal rather than a UDS request, inspect the configured path involving COM, PduR, CanIf, and the CAN driver, as well as the RTE connection to the SWC. The exact direction and route depend on whether the ECU is transmitting or receiving and on its generated configuration. Do not assume that every CAN payload passes through Dcm or CanTp: those modules serve diagnostic communication, while COM handles application signals.
A repeatable workflow for tracing a CAN fault
- Classify the symptom. Decide whether the issue is a missing signal, malformed payload, timeout, rejected diagnostic service, incorrect session, or missing or persisted DTC. This narrows the relevant path before you change configuration.
- Check the SWC and RTE contract. Verify the relevant ports, sender/receiver or client/server mapping, and generated RTE interfaces. If the application is not producing or receiving the expected data at this boundary, a CAN driver change is unlikely to address the cause.
- Check COM and PduR configuration. For signal traffic, inspect the COM signal and I-PDU setup; then verify PduR routing. For diagnostic traffic, verify the configured route toward CanTp and Dcm. Because PduR forwards rather than interprets the payload, investigate a routing mismatch before changing application logic.
- Check transport and CAN access. For multi-frame diagnostics, examine CanTp segmentation and flow control. For frame-level problems, continue through CanIf to the CAN controller and driver.
- Check Dcm for UDS failures. Verify session state, timing, service permissions, and response handling. A request that reaches Dcm can still be rejected or answered differently because of diagnostic configuration.
- Check Dem for fault-memory symptoms. Inspect event qualification, DTC status, freeze-frame or extended data, and NVRAM persistence. Dem’s role is fault-memory management, not forwarding the original CAN request to Dcm.
- Compare ECU self-diagnosis with tester results. Online diagnosis monitors component status and stores trouble codes; offline diagnosis uses external diagnostic facilities to read ECU information. A difference between the two can help distinguish an ECU fault-memory or reporting issue from a tester-to-ECU communication issue.
Configuration values: examples, not AUTOSAR defaults
Infineon’s DRIVECORE documentation gives a CAN baud rate of 500 kbps and example diagnostic identifiers of physical request 0x703, functional request 0x7DF, and physical response 0x70A. These are values in that documentation’s example configuration, not universal AUTOSAR defaults. Compare them with the ECU’s actual network and diagnostic configuration before using them to interpret a trace.
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The cited Dcm description references ISO 14229-1, ISO 15031-5, ISO 15765-4, and SAE J1979. Infineon’s CanTp description references ISO 15765-2. Those standards references explain the context of the implementation; they do not establish that every ECU supports every service or uses the same identifiers.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How to compare two AUTOSAR implementations
When two ECUs behave differently, compare their configured boundaries and responsibilities rather than assuming the module names guarantee identical behavior.
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- Layer boundary: Identify whether the difference is in the SWC, RTE mapping, upper BSW, or hardware-dependent CAN layers.
- PDU routing ownership: Compare which routes PduR is configured to forward and between which modules.
- Transport behavior: Compare CanTp configuration and behavior for segmentation and flow control.
- Diagnostic behavior: Compare Dcm session, timing, and service configuration.
- Fault-memory behavior: Compare Dem event qualification, DTC status handling, retained data, and persistence.
- Network configuration: Compare CAN identifiers and baud rate against each ECU’s actual configuration, not against another project’s example values.
- Hardware dependence: Separate differences in the hardware-independent upper interfaces from those in MCAL and CAN drivers, which depend on the microcontroller and ECU hardware.
Version and evidence context
AUTOSAR’s R24-11 layered-architecture document is the current-version reference identified for layer responsibilities here, while the Renesas and Infineon material describes layer and CAN-stack roles. The EE Times explanations date to 2010; use them for the stated conceptual descriptions, not to infer present-day AUTOSAR feature availability from their version 3.1 discussion. The CAN IDs and baud rate above are explicitly project examples from Infineon documentation.
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