CAN Bus Failure on Engine's Display

CAN Bus Failure

Figure 1.1 - CAN Bus Failure (Murphy PowerView)

Definitions of CAN Bus:

Controller Area Network (CAN) is a serial bus that connects multiple electronic control modules (ECM’s) or components together to send or receive messages in order to facilitate correct Machine/Engine operation. This data link consists of two copper wires twisted as a pair, with approximately one twist per inch (40 twists per meter). Often this twisted pair is shielded, but not always. One wire of the pair is designated as CAN High (+), and the other wire is designated as CAN Low (-). CAN data link transfers real time communication between control units (ECM’s, displays, service tools, and other components that require network communication for proper operation).

Figure 1.2 - A typical CAN bus

CAN is a simple two-wire differential serial bus—information is transferred using a differential voltage between CAN High and CAN Low. Voltages of both CAN High and CAN Low are relative to shield or ground. The formula used to define the relationship of the differential to these relative voltages is:

*CAN diff = CAN high - CAN low

CAN Buses can have one of two logic states—dominant and recessive. Typically, the voltage level associated with recessive (logic state "1") is 2.5 V for CAN High and Low. Voltage levels for dominant information (logic state "0") are 3.5 V for CAN high and 1.5 V for CAN low. The voltage level on the bus is recessive (2.5 V) when the bus is idle.

The CAN Bus is terminated with a 120 ohms resistor on each end. These resistors aid in keeping the total circuit impedance to 60 ohms (two 120 ohms resistors in parallel=60 ohms).


CAN Bus Failure - Engine Controller
When this diagnostic code occur, the following responses will occurs:
• Engine display NOT detect the ECM on the CAN bus (J1939 CAN System).
• Engine will NOT STARTS (Cranking only).

A. Murphy PowerView Display:
→CAN Bus Failure, as Figure 1.1 above
→No Parameter Received

Figure 1.3 - No Parameter Received

→NO DATA on all Engine parameters

Figure 1.4 - No Data (All Parameters)

B. CAT Messenger Display:
→Only "Engine Speed" and "Desired Engine Speed" are displayed (with **** values).

Figure 1.5 - Engine Speed (**** RPM)

C. Electronic Engine Commander (EEC) on Detroit Engine:
→EEC's Information Center Message Display: EEC Data Fault

Figure 1.6 - EEC Data Fault

D. Detroit Diesel - Electronic Controls (Electronic Display Module/ EDM) on Detroit Engine:

→All Parameter values will be 0 (zero).

Figure 1.7 - EDM (Zero values)

#Perform the Following Test Procedures:
Test Step 1. TEST THE HARNESS
→Turn the main disconnect switch to the OFF position.
→Inspect all harness connections that are related to the CAN Bus. Make sure that connectors are clean and tight.
→Check each pin and each socket of the engine harness connector. Ensure that the contacts are properly installed.

Test Step 2. CHECK THE TERMINATION RESISTORS
→Check and measure the resistance for CAN Bus (expected result: 120 ± 12 ohms).

Test Step 3. CHECK THE INPUT VOLTAGE
→Check and measure the input voltage to the ECM, both (+) "Battery Unswitched" and "Battery Switched (Keyswitch/ Ignition)", and the (-) Battery/ Ground.


Read More:
Operating the Detroit Diesel Electronic Engine Commander (EEC)
Open Fault Codes on DETROIT Engine using Detroit Diesel Diagnostic Link (DDDL)

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