Error code · Trucks: SPN codes

SPN 1231 — CAN bus 2 (J1939)

Don’t put off the repair

Open this code in the appDownload the app

A fault code doesn’t yet mean the unit or sensor itself is faulty: often it’s the plug and connector leading to it.

What you can do yourself

  1. This is the second communication bus between control units.
  2. Check the bus connectors and wires, and the power and ground of the control units.
  3. Often the cause is one faulty control unit or a corroded connector.

Stop and don’t drive on if:

  • The instrument panel went dark or many warning lights came on at once
  • Power steering is gone or the brakes don’t work as usual

Add the FMI — the second number of the code. It shows what exactly is wrong with the parameter.

Source: SAE J1939-71: J-1939 SA/SPN/FMI Descriptions (static.nhtsa.gov, MC-10141869)

The explanation comes from the error code reference in the AvtoElektrik PRO app.

The second number, FMI: what exactly is wrong

A truck code is two numbers: SPN (which part) and FMI (what is wrong with it). Tap your FMI and the app opens the meaning of that exact code.

Need a mechanic’s help?

Couldn’t fix it yourself? Oleg, an auto electrician, does computer diagnostics and repairs: he comes out anywhere in Almaty or sees you at his workshop.

Truck computer diagnostics in AlmatyCall: +7 701 121 11 10

Want to figure it out yourself?

Oleg’s course “Car computer diagnostics with a scan tool”: how to hook up a scanner, read codes and live data, and use them to find the cause. The first lessons are free.

Scan tool diagnostics course →

Nearby codes

All codes in Trucks: SPN codes →

Who keeps this reference

The reference is kept by Oleg Dmitriev, an auto electrician from Almaty with 26 years of experience: computer diagnostics of cars and trucks, repair of control units (ECUs). Can’t find the cause? Message him.

Oleg’s auto electrician websiteWhatsApp +7 701 121 11 10