AEL01 Electrical Diagnostics Resources

What is the difference between an event code and a diagnostic trouble code?

Event codes indicate an issue related to engine operation. Diagnostic trouble codes indicate an issue related to a specific sensor.

Which type of fault code informs a technician of a fault that has occurred?

A logged diagnostic code

Which type of communication is used by Caterpillar proprietary identifier standard?

Cat Data Link (CDL)

Which three code acronyms are used by a J1939 diagnostic code?

MID - SPN - FMI

What does CID mean in the code Acronyms?

Component Identifier: This part of the code indicates the specific circuit or system in which a problem was detected.  This is part of Caterpillar proprietary identifier standards.

What does MID mean in the code Acronyms?

Module Identifier: This part of the code is unique for each module communicating on the data link.  This is part of both SAE J1939 and Caterpillar proprietary identifier standards.

What does EID mean in the code Acronyms?

Event Identifier: This part of the code is used to indicate an event.  Events are valid signals that are outside of an acceptable range, such as overheating and overspeed.  This is part of Caterpillar proprietary identifier standards.

What does SPN mean in code acronyms

Suspect Parameter Number: This part of the code is similar to a CID for Caterpillar equipment using a J1939 CAN data link.  This is part of SAE J1939 standards.

What does FMI mean in code acronyms

Failure Mode Identifier: This part of the code indicates the type of problem that has been detected within the circuit or system.  This is part of both SAE J1939 and Caterpillar proprietary identifier standards, and the value of the identifier has the same meaning for both J1939 data links and CDLs.

What does WCI mean in code acronyms

Warning Category Indicator: This part of the code indicates the severity of a DTC, with 1 being the lowest severity and 3 being the highest.  This is part of Caterpillar proprietary identifier standards.

How can you identify a CAT diagnostic code?

The absence of a prefix indicates it is a CAT diagnostic code

What does the three-digit number in a CAT diagnostic code represent?

The component identifier

What does FMI stand for in a CAT diagnostic code?

Failure Mode Identifier

In the code 190-4 what does FMI 4 indicate?

The voltage is below normal

What does MID stand for in a CAT diagnostic code?

Module Identifier

In the example MID 36, which module is being identified?

The engine module

How can you identify a CAT Event Code?

The presence of an E before the three digit number identifies it as a CAT Event Code

What does the three digit number in a CAT Event Code represent?

The event identifier

What does the number in brackets after a CAT Event Code Indicate?

The warning category/ severity level

In the example E644 (2), what does the number 2 indicate?

Moderate Severity

What does MID represent in a CAT Event Code

The module Identifier

In the example E644 (2) MID 81, what module does MID 81 identify?

The transmission

How can you identify a J1939 Public Diagnostic Code?

The presence of a J before the three digit number identifies it as a J1939 Public Diagnostic Code

What does the three digit number in a J1939 public diagnostic code represent?

The suspect parameter number (SPN)

What does the number after the three digit number represent

The failure mode identifier

In the example J177-3 what does FMI 3 indicate

The voltage is above normal

What does MID represent

The module Identifier

In the example J177-3 MID 297, what does MID 297 identify?

The transmission ECM

Is the MID for transmission ECM always the same between CAT Event Codes and J1939 codes?

No, The module identifier can be different between the two code systems

How can you identify a J1939 manufacturer specific diagnostic code?

The presence of a “K” before the six-digit number indicates that the code is within the manufacturer-specific space.

What does the six-digit number in a J1939 Manufacturer Specific Diagnostic Code represent?

The Suspect Parameter Number (SPN).

What does the number after the six-digit SPN represent?

The Failure Mode Identifier (FMI).

In the example K524287-3, what does FMI 3 indicate?

The voltage is above normal.

What does MID stand for?

Module Identifier.

What does the MID tell you?

It identifies the module or ECM associated with the code.

In the example K524287-3 MID 263, what does MID 263 identify?

The Engine ECM.

Is the MID for the Engine ECM the same in CAT diagnostic codes and J1939 manufacturer-specific codes?

No. The MID number can be different depending on the code system being used.