Ambient vs intake air temperature
It's easy to mix these up. An intake air temperature sensor measures the charge going into the engine, and the fuel and ignition corrections lean on it heavily. An ambient sensor measures outside air. It's useful for logging and for comparing intercooler efficiency against outside conditions. Temperature-driven functions such as air conditioner control and the thermofan have their own setup pages.
Most temperature sensors are simple two-wire thermistors: one wire carries the signal to an ECU input and the other goes to signal ground. The resistance changes with temperature, and the ECU turns that into a voltage using a pull up resistor.
Wiring tab
Input Type
| Option | Choose it when |
|---|---|
| Analogue Voltage | The sensor puts out a signal that varies between 0 and 5V |
| Analogue Resistance | The sensor itself is a varying resistance, as a typical two-wire thermistor is |
| Thermocouple Type K | You're reading a K-type thermocouple through a Haltech TCA amplifier, like the TCA2 |
Choosing an input
An AVI (analog voltage input) is the preferred choice. If you've run out of AVIs, an SPI (synchronized pulsed input) can stand in.
| Setting | On an AVI | On an SPI |
|---|---|---|
| Pull up | 1k Ohm to 5V | Weak 10k Ohm to 5V |
| Sensor Type | Not applicable | Set to Hall Effect when reading an analog sensor |
| Calibration | Pre-installed calibrations work as supplied | Pre-installed calibrations need adjusting, because the pull up value is different |
Should the pull up be on?
Our rule of thumb:
- Two-wire sensor wired only to the Haltech: turn the pull up on. The thermistor needs it to produce a usable voltage.
- Sensor with its own power supply: turn it off.
- Sensor shared with a factory ECU, as in a piggyback install: turn it off. The factory ECU already provides the pull up, and adding a second one will skew both readings.
Calibration tab
ESP ships with a library of sensor calibrations. Use the yellow folder (Open) icon at the top left to load one, and the blue disk icon beside it to save your own. If your sensor isn't in the library, build a custom calibration from the manufacturer's data, then save it so the next install is a two-click job. A Haltech air temperature sensor is the easy choice since its calibration is already there.
After loading a calibration, let the car sit with the engine off and compare the reading to a known outside temperature. If it's way off, check the pull up setting before blaming the calibration.
Diagnostics tab
These limits let the ECU flag wiring faults and suspicious readings. Each one is disabled by default, and if Engine Protection is active you can also give each one a DTC severity.
| Limit | DTC | Catches | Our advice |
|---|---|---|---|
| Raw Min | P0070 | Voltage too low: usually a short to ground | Enable, set just below the lowest voltage the sensor can genuinely produce |
| Raw Max | P0071 | Voltage too high: usually an open circuit or unplugged sensor | Enable, set just above the highest genuine voltage |
| Operating Min | P0072 | A sudden, implausible drop in air temperature | Optional. Useful as a plausibility check |
| Operating Max | P0073 | A sudden spike in air temperature | Optional. Handy for spotting heat soak or a sensor mounted too close to a heat source |
Ambient temperature rarely warrants an engine protection action on its own. We usually log these as warnings and keep the protection severity for sensors that directly affect fueling.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reads extremely cold, won't change | Open circuit or unplugged sensor. Also confirm the pull up is on for a two-wire sensor |
| Reads extremely hot | Signal shorted to ground |
| Reads plausible but consistently off | Wrong calibration, SPI used with an AVI calibration, or double pull up on a shared sensor |
| Climbs after the car stops | Sensor is picking up engine bay heat; relocate it into clean airflow |
FAQ
Can I use an intake air temp sensor as an ambient sensor?
Yes. The sensor doesn't care what air it's in. Just load the matching calibration and mount it where it sees outside air, away from the radiator and exhaust.
Why does my reading change when I move it from an AVI to an SPI?
The SPI uses a 10k pull up instead of 1k, so the voltage for any given temperature is different. The calibration has to be adjusted to suit.
