J1939 CAN Bus & Sensor Diagnostics
Instructor-led training for diesel technicians and apprentices
About the class
A practical course on the J1939 network and the sensors that report to it. Technicians learn how modules share the CAN bus, what SPN and FMI codes really mean, and how sensor, wiring and exhaust sensor faults show up - then put it to work in the shop with purposeful, repeatable tests.
Why this training matters
Flickering lamps, lost dash data, a scan tool that can't connect, or a sensor code that keeps coming back can all have more than one cause. Weak batteries, an open circuit or a bad connection can look like a failed module. Knowing how the system works helps technicians find the fault before replacing parts.
Overall learning outcome
Given OEM service information, a truck or engine with a J1939 network, and the right tools, technicians will explain how the network and its sensors work and complete a safe test sequence that proves the cause of a fault before any part is replaced.
| J1939 | 8 outcomes | Hands-on |
|---|---|---|
| Network operation, testing and diagnosis | From batteries to exhaust sensors | Three shop stations and a workbook |
What technicians will be able to do
- Test batteries first - load test, conductance test and state of charge.
- Explain the J1939 network - twisted pair, two 120 Ω resistors, who sends and who listens.
- Test at the 9-pin DLC - voltage, resistance and shorts, and what each reading means.
- Read SPN and FMI codes - and know what a code does and doesn't tell you.
- Identify sensors and circuit faults - sensor types, pull-up and pull-down circuits, the four faults.
- Prove the cause - use the fault code state change to separate sensor, wiring and ECM.
- Test wiring under load - DMM, Load Pro leads and pin drag tests.
- Understand exhaust sensors - temperature, NOx, DEF quality and soot sensors.
Course outline
| Module | Covers |
|---|---|
| How the network works | CAN bus, resistors, messages |
| Diagnosing the network | Batteries first, DLC tests, isolate |
| SPN and FMI codes | Code structure and FMI groups |
| Sensor circuits and monitoring | Sensor types, faults, Load Pro |
| Sensors and pinpoint testing | Voltage window, state change |
| How exhaust sensors work | Temperature, NOx, DEF, soot |
What the class includes
- Instructor-led learning - clear explanations and animated walk-throughs of each system.
- Shop practical - sensor ID, circuit testing, batteries and CAN checks.
- Learner resources - fill-in-the-blank workbook and shop record sheets.
- Review and feedback - check questions and a sign-off checklist.
Book this class
Need a custom track?
Combine Jaltest onboarding with emissions, electrical, or HPCR refreshers. We routinely build blended agendas for growing fleets and dealer networks.