Why some signals can't go over CAN
Haltech's CAN devices, including the Nexus IO16, the Nexus PD16 and the Platinum IO12, give an ECU far more inputs and outputs than it has pins. For things like fans, pumps, switches and temperature sensors, the tiny delay of sending data over CAN doesn't matter.
Some signals are different. The engine needs them updated as fast as possible, and it can't safely run if they disappear because a CAN wire gets damaged or a device drops off the bus. Those have to be wired to the ECU itself. NSP enforces this: it won't let you assign these functions to CAN I/O.
Functions that must be wired to the ECU
| Function | Includes |
|---|---|
| Load sensing | Manifold pressure sensor, throttle position sensor, mass air flow sensors 1 and 2 |
| Drive by wire throttle | The throttle motor, throttle position sensors and pedal position sensors |
| Electronic wastegate | The wastegate motor and its position sensor |
| Boost control sensors | Wastegate pressure, boost pressure and pre-intercooler boost pressure sensors |
| Flat shift | The flat shift function |
| Oil metering pump | The rotary oil metering pump |
What this means when you plan a harness
Count these signals first when you're picking an ECU. If the ECU doesn't have enough native inputs and outputs for all of them, an expander won't fix that. You need a bigger ECU. Once the critical items have native pins, move everything else (fans, fuel pumps, dash switches, extra temperature and pressure sensors) onto expanders to free up ECU pins.
A simple test we use: if losing the signal for a split second could cause a sudden change in power, throttle opening or boost, wire it to the ECU. That's also why DBW is on the list. A throttle that can't hear its pedal is a safety issue, not just a tuning one.
Keep the CAN bus itself tidy: twisted pair, proper termination and good connectors. Even with the critical signals on the ECU, a flaky bus causes headaches. Our Haltech CAN system guide covers the basics.
More on the expander in our Nexus IO16 guide. Not sure how to split your I/O? Ask us and we'll help plan it.
