SPN 231 – FMI 12 (J1939 Data Link Failure Code 55) Troubleshooting Guide

Engine Check – Code 55 (12V2000 Detroit Engine)

Related Product

SPN 231 – FMI 12

J1939 Data Link Failure: Detected by ECM (Master/Receiver).

SPN 248 – FMI 8

Proprietary Data Link Failure: Detected by ECM (Master).

SPN 248 – FMI 9

Proprietary Data Link Failure: Detected by ECM (Receiver).

1. Flash Code 55 Description

Flash Code 55 indicates a fault in the J1939 data link. In multi-ECM engines, this code can be logged in different ECM sections, identified by the SID.

Common Causes:

Incorrect programming
Wiring fault
ECM failure

2. SAE J1587 Equivalent Codes

Flash Code 55 (SAE J1587 Equivalents):

SPN 231/12: J1939 data link fault
SPN 248/8: Proprietary data link fault (Master)
SPN 248/9: Proprietary data link fault (Receiver)

3. Troubleshooting Flash Code 55

(A) Test Step 1: Determine the Fault

Turn the ignition ON.
Connect the DDDL and read active codes. Read More: How to Connecting the DETROIT Engines using Detroit Diesel Diagnostic Link (DDDL)

If SPN 231/12 appears, proceed to Test Step 2.
If SPN 248/8 or 248/9 appears, proceed to Test Step 4.

(B) Test Step 2: Check for Nodes

Inspect the six-pin communication harness at the ECM:

If wiring is present, go to Test Step 3.
If no wiring exists:

Verify and/or replace the termination resistor (120 ohms).
Modify the transmission definition to an alternate option and revert to the correct setting.
Replace the ECM if necessary.

(C) Test Step 3: Check the ECM

Unplug the communication connector.
Turn the ignition ON.
Use the DDDL to read active codes:

If no active codes display, the issue lies in the OEM wiring or connected devices.
If SPN 231/12 persists, replace the ECM.

(D) Test Step 4: Check for Short

Turn the ignition OFF.
Disconnect all engine sensor harness 30-pin connectors.
Measure resistance between L3 (925) and M3 (926) on each connector:

A reading less than 5 ohms indicates a short; repair it.
If all readings are greater than 5 ohms, proceed to Test Step 5.

(E) Test Step 5: Check for Open

Insert a jumper wire between L3 and M3 on the Master ECM connector.
Measure resistance between L3 and M3 of other connectors:

A reading greater than 5 ohms indicates an open circuit in wire 925 or 926; repair the open.
If all readings are less than 5 ohms, replace the ECM.

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