What a baro sensor does for you
Barometric pressure is the pressure of the air around the car. It drops as you climb in altitude and moves up and down with the weather. Less ambient pressure means less air per intake stroke and, on a turbo car, a turbo that has to work harder to reach the same absolute boost. Giving the ECU a baro reading lets you correct for that in the tune and see it in your datalogs, which makes comparing a run in the mountains with one at sea level much more honest.
An external baro sensor is a powered three-wire part: 5V supply, signal back to the ECU, and signal ground. A MAP sensor that's open to the atmosphere, rather than plumbed to the manifold, works perfectly well as one. A 1 bar GM MAP sensor is a common choice.
Choosing an input type
The first decision in ESP is where the reading comes from. The default is On-board Pressure Sensor.
| Input Type | Where the reading comes from | When we use it |
|---|---|---|
| On-board Pressure Sensor | The Elite's internal 3.0 bar MAP sensor | Only when the internal sensor isn't being used for manifold pressure, for example on a car running an external MAP sensor |
| Analogue Voltage | An external sensor wired to an ECU input | Whenever the internal sensor is busy reading the manifold, which is most boosted builds |
The internal sensor can't do both jobs at once. If it's plumbed to the intake manifold, you need a separate sensor for baro. See our note on the internal MAP sensor for how it's plumbed.
Wiring an external sensor
With Analogue Voltage selected, pick an input on the Wiring tab.
- AVI (Analogue Voltage Input): the preferred choice. Its pull-up option is a 1k resistor to 5V.
- SPI (Synchronised Pulsed Input): a fallback when you've run out of AVIs. Set Sensor Type to Hall Effect, since that's how an SPI reads an analog signal. Its pull-up is a weaker 10k resistor to 5V.
For a baro sensor the pull-up should almost always be off. The sensor has its own 5V supply and drives its own output, so a pull-up would just skew the reading. Pull-ups are for two-wire temperature sensors that need the ECU to supply the reference. The other time to leave it off is when the sensor is shared with a factory ECU, which will already be providing whatever pull-up the circuit needs.
Display settings
- Warning Minimum: any gauge showing baro pressure flashes red when the reading falls below this. A sensible floor catches a failed or disconnected sensor at a glance.
- Display Maximum: the top of the gauge scale. It's cosmetic and doesn't change how the sensor is read.
Calibration
The Calibration tab only appears with an external sensor (Analogue Voltage). ESP ships with a library of calibrations, and you load one with the yellow Open icon. If your sensor isn't there, build a custom voltage-to-pressure calibration from the manufacturer's data sheet and save it with the blue Disk icon, so you can reuse it on the next car.
Diagnostics
These two checks catch wiring faults, and both only apply to an external sensor. Both are disabled by default.
| Setting | Code | What trips it | Our advice |
|---|---|---|---|
| Raw Min | P0228 | Voltage below your set value | Enable it, set just below the lowest voltage the sensor can produce in real conditions. Catches an open circuit or short to ground |
| Raw Max | P0229 | Voltage above your set value | Enable it, set just above the highest real reading. Catches a short to 5V or a lost ground |
With engine protection enabled, you can also assign each fault a DTC severity so the ECU responds the way you want. The full list of codes lives in our DTC index.
Troubleshooting
| Symptom | Usually |
|---|---|
| Baro reads the same as boost | On-board Pressure Sensor selected while the internal sensor is plumbed to the manifold |
| Reading is plausible but a little off | Pull-up enabled on a powered sensor, or the wrong calibration loaded |
| P0228 or P0229 on startup | Unplugged connector, broken 5V or ground, or Raw limits set too tight |
| Reading jumps around | Sensor port picking up underhood air turbulence, or a poor ground |
Mount an external baro sensor somewhere it sees still ambient air, away from the turbo inlet and cooling fan blast. If you're setting up boost control on a car that travels between altitudes, it's one of the cheapest upgrades you can make.
