Why the ECU cares about air temperature
Hot air is thinner than cold air, so the same manifold pressure carries less oxygen on a 100°F afternoon than on a cool night. The Elite reads the intake air temperature (IAT) sensor and adjusts fueling so the mixture stays where you tuned it. It's also a key channel on boosted cars, where it tells you how well the intercooler is keeping up.
Most IAT sensors are simple two-wire thermistors. One wire goes to an analog input on the ECU and the other to signal ground. The resistance changes with temperature, and the ECU converts the resulting voltage into degrees using a calibration.
Wiring tab
Input type
| Option | Use it when |
|---|---|
| Analogue Voltage | The sensor produces a 0 to 5 V signal |
| Analogue Resistance | The sensor is a variable resistance, like a typical thermistor |
| Thermocouple Type K | You're reading a thermocouple through a Haltech TCA box |
Choosing the input
Assign the sensor to an AVI (Analogue Voltage Input). That's what the calibrations are built around, and it's what we use unless there's truly nothing left. If every AVI is taken, an SPI (Synchronised Pulsed Input) can stand in. When you use an SPI, set its Sensor Type to Hall Effect, since that's the setting for any analog signal on an SPI.
The two input types use different pull-up resistors (1k on an AVI, a weaker 10k on an SPI). The bundled temperature calibrations assume the AVI, so on an SPI they will read wrong until you adjust the calibration. Check the reading against a known temperature before you trust it.
The pull-up setting
A two-wire thermistor has no power of its own. The pull-up resistor feeds it a reference from 5 V so there's a voltage to measure. The rule we follow:
- Enable it for a normal two-wire temperature sensor wired only to the Elite.
- Disable it for any sensor with its own supply.
- Disable it when the sensor is shared with another ECU, such as a factory computer in a piggyback setup. That ECU already provides a pull-up, and doubling it throws the reading off for both.
Calibration tab
This is where the voltage-to-temperature curve lives. ESP ships with calibrations for a number of common sensors. Load one with the yellow Open icon. If your sensor isn't listed, build a custom curve from the manufacturer's resistance or voltage data, then save it with the blue Disk icon so you can reuse it on the next car. If you're buying a sensor, Haltech's small thread and large thread air temperature sensors are the ones we reach for.
Display tab
- Warning Maximum: above this temperature, IAT readouts in ESP flash red. Set it where you'd want to know something is wrong, such as heat soak or an intercooler that can't keep up.
- Display Maximum: the top of the scale on ESP gauges. It only changes the display, not the sensor reading.
Diagnostics tab
These optional checks catch wiring faults and abnormal readings. All four are off by default. With Engine Protection active, each one can also be given a DTC severity so the ECU reacts rather than just logging a code.
| Setting | Code | What it catches | Our advice |
|---|---|---|---|
| Raw Min | P0112 | Voltage below your limit, which points to a short or a wiring fault | Enable it. Set just below the lowest voltage the sensor ever produces |
| Raw Max | P0113 | Voltage above your limit, which points to an open circuit or a disconnection | Enable it. Set just above the highest normal voltage |
| Operating Min | P0110 | Air temperature lower than expected, such as a sudden drop | Optional. Useful for flagging a sensor reading implausibly cold |
| Operating Max | P0111 | Air temperature higher than it should be, such as a sudden spike | Worth enabling on boosted engines, with a mild severity to start |
Look at a log of normal driving to find real voltage limits before you set the raw thresholds. That way they trip on a fault, not on a cold morning.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reads extremely cold, won't change | Open circuit or unplugged sensor. With the pull-up on, an open circuit pulls the voltage high |
| Reads extremely hot | Signal wire shorted to ground |
| Reads a steady offset from reality | Wrong calibration, pull-up setting wrong, or the sensor is on an SPI without a calibration change |
| Reading climbs at idle and falls when driving | Heat soak. The sensor is near the engine or turbo, or it's reading body temperature rather than airflow |
For a deeper walk through temperature sensor faults, see our temperature sensor diagnosis guide. The coolant temperature sensor is set up in almost exactly the same way.
FAQ
Where should the IAT sensor go on a turbo car?
After the intercooler, close to the throttle body, in the airflow. That measures the air the engine actually breathes.
Can I share the factory IAT sensor with the Elite?
Yes, as long as you disable the Elite's pull-up and let the factory ECU supply it. Then check the reading matches the factory ECU's.
