Guide · Speeduino

EGT on Speeduino

Speeduino reads an exhaust gas temperature amplifier on a spare analog pin, set up as a local auxiliary input. This guide covers the wiring, the TunerStudio setup, and turning the reading into °C. It uses the EGX5 and EGX12. With any other linear 0–5 V amplifier, only the scaling numbers change.

Menu names checked against Speeduino firmware 202501.7, its TunerStudio definition file and EFI Analytics' TunerStudio documentation, September 2026.

00What you need

• A Speeduino board with a free analog input, connected to TunerStudio.
• Speeduino firmware 202207 or newer. Older firmware names some menu items differently.
• TunerStudio MS Ultra to show °C. The free Lite edition shows the raw count only; use the table in step 04.
• An EGX5 if you're powering it from the 5 V sensor supply, or an EGX12 from switched 12 V. Either one needs an ungrounded Type K probe; the kits include one.
• A multimeter.

01Pick an input

Speeduino can read up to 16 extra inputs. TunerStudio picks them by pin name: A0 to A15 on Mega-based boards.

• Use a pin nothing else uses. Speeduino checks for clashes with its main sensors and outputs at power-on and shows I/O Error! in TunerStudio, but it doesn't catch every clash.
• Skip the coolant and air temperature inputs. They're already in use, and they carry a pull-up resistor meant for a thermistor.
• Check your board's pinout for which analog pins are free.
• Teensy or STM32 board? Those processors run at 3.3 V. Use one of the board's 0–5 V spare analog inputs, not a bare processor pin. On a Dropbear these need firmware 202501 or newer.

02Wire it

• Use a ground at the ECU, not chassis. Every 4–5 mV of ground offset reads as about 1 °C.
• An EGX5 goes on the 5 V sensor supply only, never 12 V. It has no reverse-polarity protection either, so check red and black before you power up.
• Both outputs stay near 5 V, even in a fault. The EGX5 can't rise above its own 5 V supply, and the EGX12 is capped at about 5.3 V.

Probe side

• Kit: the probe plugs into the mini-K socket.
• Module only: yellow to the probe's +, red to −, spliced right at the module.
• Need more reach? Extend from the probe end with Type K extension wire, never copper.
• Ungrounded probes only. An ohmmeter from either lead to the sheath should read open.
• Mount the module somewhere cool, on the cabin side of the firewall or an inner fender: under 50 °C for an EGX5, under 100 °C for an EGX12.

03Set up the input in TunerStudio

1. Open Accessories → Local Auxillary Input Channel Configuration. TunerStudio spells it that way.
2. Pick a free row, AUX Input 0 to 15, and set it to Analog_local.
3. Give it an Input Alias, such as EGT. The alias names its gauge.
4. Set Pin No to the pin you wired.
5. Burn the change, then restart Speeduino. It only sets up aux inputs at power-on, so the new input may read 0 until then.
6. Right-click a gauge on the dashboard and pick your alias from Auxiliary Input Channels.

That gauge shows a raw count from 0 to 1023, not a temperature. The next step turns it into °C.

04Turn counts into °C

Speeduino reports an aux input as a raw count from 0 to 1023 and doesn't scale it. On Mega-based boards and the Dropbear's spare inputs, 0–5 V reads as 0 to about 1023. The conversion happens in TunerStudio, and needs TunerStudio MS Ultra.

1. Open Tools → Custom Channel Editor, right-click Output Channel and add one.
2. Choose Advanced and enter auxin_gauge0 * 1000 / 1024 for an EGX5, or auxin_gauge0 * 1250 / 1024 for an EGX12. Aux input 0 is auxin_gauge0, input 1 is auxin_gauge1, and so on.
3. Add a Gauge Template and a Data Log Field for it. The channel then appears in the gauge right-click menu and is logged with every datalog.

The conversion lives only in TunerStudio. Speeduino still sees counts, so anything that runs on the ECU itself, like a programmable output, works in counts.

A dash means past that model's range. 1023 is the top of Speeduino's scale. No Ultra? Read the count off the aux gauge and look it up here.

05Optional: a high-EGT light

Speeduino can switch an output from an aux input, which makes a simple warning light.

1. Open Settings → Programmable outputs, pick a rule and a free output pin.
2. Set Condition 1 to your input, listed as Aux in 0 to Aux in 15.
3. Choose > (greater), and enter the count for your limit from the table above.
4. Burn, then restart Speeduino. It sets up output pins at power-on too.

This rule compares counts, not °C. Wire the lamp the way your board's documentation shows for that output.

06If something's wrong

The gauge stays at 0

Check that the row is set to Analog_local, the pin number is right, and Speeduino has restarted since you burned the change. Also check the pin isn't used by anything else, and that the white wire is connected. I/O Error! shows for some pin clashes, not all.

It reads near the top of the scale on a cold engine

The probe is unplugged or open. Both modules drive their output high when the probe circuit is open, so an open probe reads hot, not cold.

The reading jumps with revs, fans or the alternator

You have a grounded probe, or the black wire is on chassis ground. Fit an ungrounded probe and use a ground at the ECU.

It reads high once the engine bay heats up

The module is mounted somewhere too hot, or there's copper wire between the probe and the module.

The raw aux column is missing from your log

TunerStudio only logs raw aux inputs when secondary serial or CAN is on. Log the converted channel from step 4 instead.

Every reading is a few percent off

On a Mega-based board, the processor measures against its own 5 V supply. If that supply sits at 4.90 V instead of 5.00 V, every temperature reads 2 % high: about 18 °C at 900 °C. Measure the 5 V sensor supply with the engine running, then scale the formula to it. For an EGX5, replace 1000 with 200 × your reading (4.90 V gives 980). For an EGX12, replace 1250 with 250 × your reading (4.90 V gives 1225).