What is the emergency protocol for SPN 520210 FMI 31?

1) Pull over at the first safe location. 2) Shut down engine. 3) Check for obvious issues (fluid leaks, smoke, loose connections). 4) Scan for secondary fault codes. 5) Call roadside assistance if unable to resolve. Do not attempt to limp the vehicle to a shop.

What happens if I ignore SPN 520210 FMI 31?

Ignoring a STOP ENGINE code can result in: turbocharger failure ($3,000–$8,000), engine seizure requiring complete overhaul ($15,000–$40,000), or fire risk from leaking fuel/oil onto hot exhaust components. If this code is accompanied by low oil pressure or high coolant temperature, engine failure may occur within minutes.

🔴 STOP ENGINE

PACCAR SPN 520210 FMI 31: Meaning, Causes & Fix

Aftertreatment Control Module (ACM) — internal fault condition exists, module unable to process SCR/DPF commands per PACCAR MX-11 EPA 2017 certification

✅ {% if lang == "es" %}Control de Calidad{% else %}Quality Checked{% endif %} — 2026-07-06. {% if lang == "es" %}Cotejado con SAE J1939 y documentación PACCAR MX-11.{% else %}Cross-checked with SAE J1939 and PACCAR MX-11 documentation.{% endif %} STOP ENGINE codes receive priority editorial review.

Diagnostic Reference

Field	Details
Code	`SPN 520210 FMI 31`
Protocol	J1939 SPN: 520210 FMI: 31
Component	Aftertreatment Control Module (ACM) / CAN Bus
Manufacturer	PACCAR
Engine Series	MX-11
Severity	🔴 STOP ENGINE
SAE Reference	SAE J1939-73 Digital Annex — SPN 520210, FMI 31

Possible Causes

ACM internal memory corruption from voltage spike during jump-start (per SAE J1939-15 CAN bus immunity requirements)
ACM firmware checksum failure after interrupted update
CAN bus termination resistor at ACM location failed open (120 ohm resistor)
ACM power supply fuse blown from short in dosing valve driver circuit
Water ingress into ACM housing from windshield leak draining onto module

Diagnostic & Repair Procedure

Step 1: Check ACM power fuse in battery box: 15A fuse, replace if blown
Step 2: Verify CAN bus resistance at ACM connector: should read 60 ohms
Step 3: Attempt ACM firmware reflash with PACCAR Davie diagnostic tool
Step 4: Inspect ACM housing for water stains — module located under driver's seat
Step 5: Check battery voltage stability: must be 12.4V+ before ACM reflash

Frequently Asked Questions

Can I keep driving with SPN 520210 FMI 31?

No. This is a STOP ENGINE-level fault. Continued operation will cause severe engine damage including potential catastrophic failure. Pull over safely and diagnose before restarting. Tow the vehicle to a service facility if the root cause cannot be identified and resolved at roadside.

What is the emergency protocol?

1) Pull over at the first safe location — use hazard lights and reflective triangles if on a highway shoulder. 2) Shut down engine. 3) Check for obvious issues: fluid leaks, smoke, loose connections, unusual odors. 4) Scan for secondary fault codes using a dash display or diagnostic tool — these often point to the root cause. 5) Call roadside assistance if unable to resolve. Do not attempt to limp the vehicle to a shop.

What happens if I ignore this code?

Ignoring a STOP ENGINE code can result in: turbocharger failure ($3,000–$8,000), engine seizure requiring complete overhaul ($15,000–$40,000), or fire risk from leaking fuel/oil contacting hot exhaust components. If this code is accompanied by low oil pressure or high coolant temperature, engine failure may occur within minutes of continued operation.

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.

Estimated Labor Hours

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Estimated Parts Cost ($)

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Associated Symptoms

Engine Dies No Aftertreatment Communication All Aftertreatment Lights On Def System Inoperative Won T Start Acm Fault Acm Not Found On Scan Tool

References & Further Reading

SAE J1939-73: Application Layer — Diagnostics. SAE International. Defines SPN 520210 / FMI 31 fault code semantics for heavy-duty CAN networks. SAE J1939 Standard
PACCAR MX-11 Service Manual: OEM diagnostic procedures for Aftertreatment Control Module (ACM) / CAN Bus faults. Consult the official PACCAR 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 520210 FMI 31 is defined in SAE J1939-73 Digital Annex. Diagnostic procedures sourced from PACCAR OEM technical service documentation. Not for safety-critical decisions. Consult a certified diesel mechanic before performing any repair. See our full disclaimer.