How far can I drive with SPN 625 FMI 2?

This CHECK AT NEXT STOP code allows continued operation to a safe service location, typically within 50–100 miles. However, you should reduce engine load (avoid steep grades, reduce speed) and monitor related gauges closely. If secondary symptoms appear (smoke, noise, temperature spike), pull over immediately.

Will SPN 625 FMI 2 cause permanent engine damage if I keep driving?

If addressed promptly at the next stop, permanent damage is unlikely. However, prolonged operation (200+ miles) with this fault active can escalate the issue — for example, a DEF system fault will eventually trigger a full derate and speed limitation. Additionally, some CHECK NEXT STOP conditions can degrade into STOP ENGINE faults if the root cause worsens.

Can I clear SPN 625 FMI 2 myself or do I need a mechanic?

You can attempt the diagnostic steps outlined below. Many CHECK NEXT STOP codes have straightforward causes like low fluid levels, clogged filters, or loose connections that an owner-operator can address. However, if the code returns after clearing, the underlying fault requires professional diagnosis with a scan tool capable of viewing live data and freeze-frame information.

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🟡 CHECK AT NEXT STOP

Cummins SPN 625 FMI 2: Meaning, Causes & Fix

J1939 Multiplexing Error — erratic, intermittent, or incorrect data received from a multiplexed source on the J1939 data link

Reviewed by ASE Certified Mechanics · Last updated July 13, 2026

Quick Answer

SPN 625 FMI 2 = J1939 Multiplexing Error
Severity: 🟡 CHECK AT NEXT STOP · System: J1939 Data Link / Multiplexed Message Source · ⚠️ Drive to next stop

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Diagnostic Reference

Field	Details
Code	`SPN 625 FMI 2`
Protocol	J1939 SPN: 625 FMI: 2
Component	J1939 Data Link / Multiplexed Message Source
Manufacturer	Cummins
Engine Series	ISX15
Severity	🟡 CHECK AT NEXT STOP
SAE Reference	SAE J1939-73 Digital Annex — SPN 625, FMI 2

Possible Causes

Corroded or damaged J1939 data link connector at the engine ECM or vehicle ECU
Intermittent open circuit on J1939 CAN high or CAN low wire due to chafing
Electronic module sending erroneous multiplexed message (transmission, ABS, or body controller)
J1939 bus termination resistor missing or incorrect value (should be 120 ohms at each end)
Electromagnetic interference from nearby high-current wiring affecting CAN bus signal quality

Diagnostic & Repair Procedure

Step 1: Measure J1939 bus termination resistance — should be 60 ohms across CAN high and low
Step 2: Inspect all J1939 connector pins for corrosion or damage
Step 3: Check CAN bus wire routing for interference from high-current wiring
Step 4: Use J1939 analyzer to identify the module sending erroneous data
Step 5: Verify all modules have correct source addresses and latest firmware

Frequently Asked Questions

How far can I drive with this code?

This CHECK AT NEXT STOP code allows continued operation to a safe service location, typically within 50–100 miles. Reduce engine load (avoid steep grades, reduce cruising speed) and monitor related gauges closely. If secondary symptoms develop — smoke, unusual noise, temperature spike — pull over immediately.

Will this cause permanent engine damage if I keep driving?

If addressed promptly at the next stop, permanent damage is unlikely. However, prolonged operation (200+ miles) with this fault active can escalate the issue. For example, DEF system faults will eventually trigger a full derate and speed limitation to 5 mph. Some CHECK NEXT STOP conditions degrade into STOP ENGINE faults if the root cause worsens — do not postpone service indefinitely.

Can I diagnose this myself or do I need a mechanic?

You can attempt the diagnostic steps listed above. Many CHECK NEXT STOP codes have straightforward causes — low fluid levels, clogged filters, or loose connectors — that an owner-operator can address. However, if the code returns after clearing, the underlying fault requires professional diagnosis with a scan tool capable of viewing live data and freeze-frame information.

Estimated Repair Cost

Typical repair: $200–1,500 (Parts: $150–1,000 + Labor: 1–4 hours) · Costs vary by make/model and location

Diesel Repair Cost & Downtime Estimator

Enter estimated labor hours to calculate repair cost and potential fleet downtime losses. Based on national average diesel shop rate of $150/hr and daily revenue loss of $800/day for a parked truck.

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Related Fault Codes — ISX15

SPN 1569 FMI 31 🔴 STOP ENGINE

Engine Protection Torque Derate

SPN 102 FMI 18 🔴 STOP ENGINE

Intake Manifold Pressure critically low

SPN 111 FMI 18 🔴 STOP ENGINE

Engine Coolant Level critically low

SPN 639 FMI 9 🔴 STOP ENGINE

J1939 CAN Bus Communication Loss

SPN 1322 FMI 31 🟡 CHECK AT NEXT STOP

Misfire Detected on Cylinder 6

MID 128 SID 1 FMI 5 🟡 CHECK AT NEXT STOP

Injector Cylinder 1 Circuit

Associated Symptoms

Check Engine Light Intermittent Gauge Operation Transmission Shift Erratic Multiplexing Fault

References & Further Reading

SAE J1939-73: Application Layer — Diagnostics. SAE International. Defines SPN 625 / FMI 2 fault code semantics for heavy-duty CAN networks. SAE J1939 Standard
Cummins ISX15 Service Manual: OEM diagnostic procedures for J1939 Data Link / Multiplexed Message Source faults. Consult the official Cummins service documentation for your specific engine serial number.
TMC RP 1210: Recommended Practice for Windows-Based Vehicle Diagnostic Interface. Technology & Maintenance Council (TMC) of American Trucking Associations.

Data Provenance: This fault code definition is derived from SAE J1939 standards. SPN 625 FMI 2 is defined in SAE J1939-73 Digital Annex. Diagnostic procedures sourced from Cummins OEM technical service documentation. Not for safety-critical decisions. Consult a certified diesel mechanic before performing any repair. See our full disclaimer.