Two CAN buses, two jobs
Nexus ECUs separate their CAN traffic. The Haltech CAN system is for Haltech devices like dashes, wideband controllers and expansion modules. The Vehicle CAN system is for everything else on the car: the factory cluster and body modules, or a generic OBD-II scan tool. In NSP you pick what the Vehicle CAN bus should do with the Bus Selection setting.
Bus Selection options
| Option | What the ECU does | Use it when |
|---|---|---|
| OBD-II | Answers standard OBD-II requests with live sensor data and trouble codes | You want a scan tool or an OBD-II phone app (iPhone or Android) to read the engine |
| Vehicle | Sends factory-style CAN messages for a supported vehicle | You're replacing the factory ECU and want the gauges, cluster and other modules to keep working |
| Receive Only Mode | Listens to the bus but never transmits | The Haltech is running alongside a factory ECU that is still on the bus |
OBD-II output can be switched off if you don't want it. When you choose Vehicle, pick your car from the list, and NSP's description panel on the right shows which CAN devices are supported for that model. It's worth reading before you assume a module will work.
Why receive-only matters
CAN is a shared bus. If two ECUs both think they're the engine controller and both transmit, devices on the bus see conflicting or colliding messages, and you get flickering gauges, warning lights or modules dropping out. Receive Only Mode lets the Haltech read what it needs without adding its own messages.
OBD-II data the Nexus provides
When OBD-II is enabled, the ECU answers the standard OBD-II parameter IDs (PIDs) below. Most only respond if the related sensor or function is set up in your map, because the ECU can't report a value it doesn't have.
Engine and airflow
| PID | Data | Needs |
|---|---|---|
| 0x0C | Engine speed (RPM) | Always available |
| 0x0E | Ignition advance | Always available |
| 0x1F | Time since engine start | Always available |
| 0x42 | Control module (battery) voltage | Always available |
| 0x1C | Which OBD standard the ECU meets | Always available |
| 0x0B | Manifold absolute pressure | MAP sensor set up |
| 0x33 | Absolute barometric pressure | Baro sensor set up |
| 0x10 | Mass airflow | MAF 1 or MAF 2 enabled |
| 0x11 | Absolute throttle position | TPS or drive by wire |
| 0x0D | Vehicle speed | Speed sensor set up |
Temperatures
| PID | Data | Needs |
|---|---|---|
| 0x05 | Coolant temperature | Coolant sensor set up |
| 0x0F | Intake air temperature | Air temp sensor, or calculated air temp turned on |
| 0x5C | Oil temperature | Oil temp sensor set up |
| 0x3C to 0x3F | Catalyst temperatures 1 to 4 | The matching EGT sensor (1 to 4) enabled |
Fuel and oxygen sensors
| PID | Data | Needs |
|---|---|---|
| 0x06 / 0x08 | Short-term fuel trim, bank 1 / bank 2 | O2 closed loop control on that bank |
| 0x07 / 0x09 | Long-term fuel trim, bank 1 / bank 2 | O2 control on that bank, with long-term trim turned on |
| 0x44 | Commanded equivalence ratio (lambda) | VE fueling or O2 control enabled |
| 0x0A | Fuel rail gauge pressure | Fuel pressure sensor set up |
| 0x2F | Fuel level | Fuel level sensor set up |
| 0x52 | Ethanol percentage | Flex fuel sensor set up |
| 0x2E | Commanded evap purge | Evaporative control enabled |
| 0x14 / 0x18 | Narrowband 1 and 2 (bank 1 and bank 2, sensor 1) | The narrowband sensor set up |
| 0x26 to 0x29 | Widebands 1 to 4, reported as bank 1 sensors 2 and 3, then bank 2 sensors 2 and 3 | The matching wideband enabled |
Vehicle information requests
- 0x02: VIN.
- 0x04: calibration ID. This one is for Haltech's use and shouldn't be relied on by customers.
- 0x0A: ECU name.
If a scan tool shows a blank or missing value, check the "Needs" column first. Nine times out of ten the sensor or function simply isn't enabled in the map, so the ECU has nothing to report.
Troubleshooting
| Symptom | Usually |
|---|---|
| Scan tool can't connect | OBD-II output disabled, Bus Selection set to something else, or Vehicle CAN not wired to the diagnostic port |
| Some PIDs missing | The related sensor or function isn't set up in NSP |
| Cluster warning lights or erratic gauges with a factory ECU still fitted | Both ECUs transmitting. Use Receive Only Mode |
| A factory module doesn't respond in Vehicle mode | That device isn't supported for your model. Check the description panel |
FAQ
Can I use a cheap OBD-II Bluetooth adapter with a Nexus?
Generally yes, for the standard PIDs listed above, as long as OBD-II output is enabled and the adapter is on the Vehicle CAN bus.
Does OBD-II output make my car emissions-compliant?
No. It lets tools read data and codes. It doesn't change what the engine or its emissions equipment is doing.
More on CAN in our CAN overview and the Haltech dash OBD-II channel list, or browse the Nexus range.
