efi2000
Guide · 4 min read · updated 6 November 2026

Sensor calibration: MAP, TPS, temperature and wideband

Every table in a tune is only as good as the sensor readings behind it. How each sensor is calibrated and a quick check for each.

Why calibration comes first

The fuel calculation uses MAP, air temperature and coolant temperature directly, and autotune trusts the wideband. A MAP sensor that reads 10 kPa high makes every VE cell wrong in a way you can't tune out, and a wideband that reads half a point lean makes a correct tune look rich.

Check each sensor against something you know before you tune anything. It takes minutes.

MAP sensor

Choose the sensor type that matches the part fitted, by its pressure range: a 1-bar sensor for naturally aspirated engines, 2.5 bar or more for boost. Each firmware has presets for common sensors, or takes the pressure at 0 V and 5 V from the data sheet.

  • Check: with the key on and the engine off, MAP should read the local air pressure. About 100 kPa at sea level, about 90 kPa at 1000 m.
  • Check: at a warm idle a healthy engine pulls 30–50 kPa. Readings near atmospheric at idle point to a leak or a bad hose.
  • Use a short, sealed hose from a point in the plenum that sees all cylinders, not one runner.

Throttle position (TPS)

The ECU reads the TPS as a raw value and turns it into 0–100 % using two calibration points: throttle closed and throttle wide open. Record both with the engine off.

  1. With the throttle fully closed, record the raw reading as the closed value.
  2. Press the pedal to the floor and record the raw reading as the open value.
  3. Check the live TPS reads 0 % closed and 100 % open, and moves smoothly between them without jumps.
  4. Recalibrate whenever you adjust the throttle stop or replace the sensor.

Acceleration enrichment, alpha-N load and deceleration fuel cut all depend on TPS. A reading that sits at 2 % when closed can stop the ECU from recognising idle.

Coolant and air temperature

Temperature sensors are thermistors: their resistance falls as they warm. The ECU reads them through a pull-up (bias) resistor, and needs a curve that turns the voltage into a temperature for your exact sensor.

  • Speeduino and MegaSquirt keep the curve on the ECU, outside the tune, and load it with TunerStudio's Calibrate Thermistor Tables tool. Choose a preset (GM is common) or enter three temperature and resistance points from the sensor's data sheet, with the board's bias resistor.
  • rusEFI and epicEFI keep three temperature and resistance points and the pull-up resistor value in the tune itself.
  • Check: on a cold engine that has sat overnight, coolant and air temperature should both read the ambient temperature, within a few degrees.

Coolant temperature drives cranking fuel, warm-up enrichment and idle targets. A sensor that reads 20 °C high makes a cold engine hard to start.

Wideband oxygen sensor

A wideband controller turns the sensor's signal into an analog voltage (usually 0–5 V) or a CAN message. The ECU must use the same scale the controller outputs, or every AFR reading will be off.

  • Analog: find the controller's output scale in its manual, such as 0 V = 10 AFR and 5 V = 20 AFR, and enter the same two points in the ECU's wideband calibration.
  • CAN: rusEFI and epicEFI can read rusEFI and AEM X-series widebands directly over CAN. Turn on CAN wideband and the analog scale no longer matters.
  • Ground the controller's analog output reference at the ECU's sensor ground. A ground offset of 0.1 V shifts AFR by about 0.2 on a 10–20 scale.
  • Check: compare the ECU's reading with the controller's own display. They should agree to within 0.1 AFR.
  • Free-air calibrate the sensor if the controller asks for it, and replace it if it reads lean on a known-rich mixture.

Calibrating sensors in efi2000

efi2000 reads the sensor calibration tables an INI declares in its [ReferenceTables] section, as Speeduino's does, the way TunerStudio does. Build a thermistor curve from a preset or three points, a linear wideband curve, or load an .inc file, preview the curve and send it to the connected ECU. The ECU stores it immediately; it isn't part of the tune and has no burn. MegaSquirt's thermistor calibration is TunerStudio's own built-in tool rather than an INI table, and efi2000 doesn't offer it yet, so calibrate MegaSquirt thermistors in TunerStudio for now.

TPS calibration reads the live sensor: close the throttle and set closed, open it fully and set open. The log viewer and Live telemetry show each sensor's reading over time, so you can check MAP at key-on and coolant against ambient.

Questions

My AFR gauge and the ECU disagree. Which is right?
Usually the controller's own display, if it is a dedicated wideband. Match the ECU's calibration to the controller's analog output scale and check the sensor grounds.
Do I need to recalibrate after a firmware update?
On Speeduino and MegaSquirt, thermistor curves usually survive an update but it's worth checking coolant reads ambient afterwards. Settings stored in the tune, such as TPS and MAP, come back when you write your tune.