J1939 and WWH-OBD

Trucks, buses, agricultural and construction machines do not talk like a car. Their controllers broadcast what they know on the CAN bus (SAE J1939), and their legislated emission data is asked over UDS (WWH-OBD, ISO 27145). WiCAN PRO listens to the first and asks the second; a European truck has both on one bus, and WiCAN handles both at once.

Which is which

	OBD-II (a car)	WWH-OBD, OBD on UDS	SAE J1939
Who	Passenger cars and light vehicles	EU heavy-duty vehicles and vans (ISO 27145); US cars from model year 2027 (SAE J1979-2)	Trucks, buses, agricultural and construction machines
How the data moves	WiCAN asks, the ECU answers (010C for engine speed)	WiCAN asks over UDS (22F40C for the same value)	The controllers broadcast on their own; nobody has to ask
What WiCAN uses	The OBD chip	The OBD chip	Its own CAN interface, listening
Set up by	Quick Setup's vehicle step, or Scan PIDs	The same: WiCAN finds that 22F400 answers where 0100 is silent	Quick Setup's vehicle step hears the network, or Settings › CAN bus by hand

J1939: listening to the network

Switch the listener on

Quick Setup does this for you: its vehicle step listens to the network when no OBD answer comes, reports J1939 vehicle with the bit rate it measured, and stages the CAN interface and the listener in the one restart it asks for. By hand:

1. Settings › CAN bus › CAN Interface › Enabled

   Bit rate Automatic lets WiCAN measure the bus (most J1939 networks run at 250 kbit/s, some at 500). Keep Listen-only (silent) mode on: WiCAN never acknowledges or sends a frame on the vehicle's network.

2. J1939 (trucks, buses, machines) › J1939 on the CAN interface

3. Submit in the header. WiCAN restarts and starts listening.

Settings, CAN bus: the CAN interface and the J1939 listener.

What it hears

• Parameter groups (PGNs): the newest message of every group from every controller, long messages reassembled. Groups a controller only sends on request appear when some other node of the vehicle asks for them (an instrument cluster usually does).
• The VIN, when a controller broadcasts it (PGN 65260).
• Active trouble codes (DM1) of every controller, with the four lamps.
• Who is on the bus: each source address, its frame count and, when it claimed its address, its NAME.

The status is GET /api/j1939 (Vehicle): the state (off, no_bus when the CAN interface is off, listening), the bus verdict (j1939 once two well-known groups were seen, other after 50 frames without one), sources, values and DM1. The Parameters page shows a listener line over the table with the same facts.

Values on the Dashboard: PGN rows

A J1939 value is an ordinary parameter row whose request names a group instead of a PID. Automate › Parameters › Custom PIDs › Add PGN adds one (PGN:F004, engine speed); the row shows a J1939 tag where an RX ID would be, and Test decodes it from what the listener holds.

PGN:F004          engine controller 1, from whichever controller sends it
PGN:FEEE@0        engine temperature from source address 0 (the engine)
PGN:FEE5?         engine hours: a group only sent on request

PGN:<hex>

The group number, 1 to 5 hex digits.

@<source>

Pins one controller (0 to 253). Without it WiCAN takes the lowest address heard in the last 5 seconds, so the engine wins over a trailer.

?

A group sent on request only. In listen mode the row shows what another node asked for; in active mode (below) WiCAN asks at the row's period, once a second at most.

Expressions

B0 is the first data byte. J1939 words are little-endian, so compose them byte by byte: B3+B4*256, not [B3:B4].

Automate, Parameters, Custom PIDs: a PGN row beside an ordinary request.

WiCAN knows 21 common values by name, so a row for one of these needs no expression of its own and Quick Setup offers them as the standard set of a J1939 vehicle:

Name	SPN	Group	Unit
EngineSpeed, ActualEnginePercentTorque	190, 513	F004	rpm, %
AccelPedalPosition1, EnginePercentLoad	91, 92	F003	%
TransCurrentGear	523	F005
WheelBasedVehicleSpeed	84	FEF1	km/h
EngineCoolantTemperature, EngineOilTemperature	110, 175	FEEE	degC
EngineOilPressure	100	FEEF	kPa
IntakeManifoldPressure, IntakeManifoldTemperature	102, 105	FEF6	kPa, degC
BarometricPressure, AmbientAirTemperature	108, 171	FEF5	kPa, degC
BatteryPotential	168	FEF7	V
FuelRate	183	FEF2	L/h
FuelLevel1	96	FEFC	%
DEFTankLevel	1761	FE56	%
TotalVehicleDistanceHR	917	FEC1	km
TotalVehicleDistance	245	FEE0 (on request)	km
EngineTotalHours	247	FEE5 (on request)	hours
EngineTotalFuelUsed	250	FEE9 (on request)	L

Everything else comes from a DBC file (DBC Signals) or a PGN row with your own expression.

Not available is not a value

J1939 reserves the top of every range: FF means the controller has no such parameter, FE that it cannot measure it right now, FB a special meaning (a gear selector in park). WiCAN reports those states and publishes no value for them, so a dashboard never shows 255 degrees.

Trouble codes on a J1939 vehicle

Trouble Codes shows the active codes every controller broadcasts (DM1): SPN110-0 form, the occurrence count, the source address in the ECU column, and the four lamps (MIL, Stop, Warning, Protect) as chips. A listener clears nothing, so the page offers no clear on a J1939-only vehicle. See Trouble codes.

Active mode: when WiCAN must ask

Listening covers nearly everything. Active mode makes WiCAN a node of the network: it claims an address (249 by default, the first off-board diagnostic tool address, moving to another one when a controller contests it), answers requests addressed to it, and can ask:

• the groups sent on request (? rows: engine hours, total distance, fuel used) at the row's period;
• the VIN during vehicle detection;
• previously active codes (DM2) for the Trouble Codes report, and the clears (DM11, DM3) when clearing is allowed.

Under Settings › CAN bus › J1939 › Show advanced: Mode Active and the Preferred address. The CAN interface must then run in normal mode (Listen-only off), because a node has to acknowledge frames. Use it when a value you need is only sent on request; on a vehicle you merely want to watch, stay in listen mode.

WWH-OBD and OBD on UDS

Nothing to set. Vehicle detection asks 0100 and 22F400; the one that answers decides the dialect, and WiCAN remembers it with the car. From then on:

• Standard PIDs are 22F4xx requests. Each row carries the ECU that owns the value (22F40C · ECU 58 on the Parameters page), because the same PID can come from several ECUs on such a vehicle.
• The VIN is read with 22F802 (or 22F190).
• Trouble Codes shows the path OBD on UDS (ISO 27145): confirmed and pending codes, permanent codes, every ECU parsed apart. The legislated clear wipes the emission codes of every ECU, like mode 04 on a car.
• Profiles work as on any car; standard and vehicle-specific rows can mix.

An EU truck answers WWH-OBD and broadcasts J1939 on the same bus: its record carries the UDS dialect and the J1939 flag, its table holds 22F4xx rows beside PGN: rows, and its DTC report lists the UDS codes with the DM1 codes. Quick Setup adds a J1939 network as well note when it finds one.

Troubleshooting

Symptom	Likely cause	What to do
State no_bus	the CAN interface is off	Settings › CAN bus › Enabled, Submit
Bus verdict other	not a J1939 network, or the wrong bit rate	Bit rate Automatic; check the connector carries the J1939 bus (some vehicles have it on other pins than the diagnostic CAN)
No sources, no values	the network is quiet: ignition off	ignition on; many controllers only broadcast with the engine running
A ? row never updates	listen mode, and nobody else asks for that group	active mode, or drop the row
Values freeze for a while and resume	the controller stopped broadcasting; WiCAN keeps the last value and marks its age	nothing
queue_drops grows in the status	the bus is busier than the listener's queue in bursts	normal on a loaded bus; the stored messages are still the newest