Guide · Holley EFI

EGT on Holley EFI

Holley's Terminator X, HP and Dominator ECUs read an exhaust gas temperature amplifier on one of their 0 – 5 V inputs, set up as a custom 5 V sensor. This guide covers which inputs work, the wiring, the software setup in °F, and warnings. A standard Sniper and Sniper 2 have no 0 – 5 V input.

Checked against Holley's ECU wiring manuals, its I/O module and software documentation, and its sensor diagnostics guide, September 2026.

00What you need

• A Terminator X or X Max with the Terminator X software, or an HP or Dominator with the Holley EFI software. On a Super Sniper, Inputs #3–#5 work too, set up in the Sniper EFI PC software. A standard Sniper and Sniper 2 have no 0 – 5 V input.
• An EG5 for the ECU's Sensor +5v, or an EG12 for switched 12 V.
• A Type K probe and a bung or O2-port adapter for it, bought to the specifications under Recommended to use with.
• A multimeter.

Electrical

01Pick an input

Terminator X, X Max and HP have four inputs on the I/O connector, and all four take 0 – 5 V. Dominator has dozens, but not all take 0 – 5 V: use one whose Pin Map symbol includes a 5.

• Terminator X I/O connector: Input #1 is pin A (white/blue), #2 pin B (white/red), #3 pin C (white/black) and #4 pin D (white/green). Input #1 comes set up for A/C kick, so use #2, #3 or #4 unless you remove that.
• J1A pins on HP, Dominator, Terminator X and X Max: Input #1 A12, #2 A3, #3 A13, #4 A4.
• Dominator has more inputs on J2A, J3 and J4. Input #5, for example, is J2A-A10.
• Super Sniper: Inputs #3–#5 on the 8-pin connector: C violet, D pink, E dark green.
• Out of inputs? Holley's CAN I/O module, 554-165, adds eight, including 5 V analog inputs.

02Wire it

• Use the Sensor +5v and Sensor Ground on the same connector as your input. Each Holley connector with 0 – 5 V inputs has its own, and so does the CAN I/O module. Holley says not to use 5 V or ground from other controllers.
• EG12: use a clean switched 12 V source that stays live while cranking.
• Use the sensor ground, not chassis. Every 4 – 5 mV of ground offset reads as about 1 °C.
• An EG5 goes on a 5 V sensor supply only, never 12 V. It has no reverse-polarity protection either, so check red and black before you power up.
• Neither output can go much above 5 V. The EG5 can't rise above its own 5 V supply, and the EG12 is capped at about 5.3 V.

Probe side

• The thermocouple cable is cut square. Take the jacket back, strip the yellow and red, and splice yellow to the probe's + and red to −. The cable is Type K extension, so the splice can sit anywhere along its run.
• Check the polarity. A reversed probe reads right at room temperature, so once it is spliced, warm the probe's tip: the reading must rise. If it falls, swap the probe's two leads at the splices. On a probe whose leads are not marked, the − lead is the one a magnet sticks to.
• 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 EG5, under 100 °C for an EG12.

Software

03Set it up in the Holley software

1. Open the I/O ICF. If there's no I/O icon, add one: Toolbox → Add Individual Config → IO → Base Config - Blank.io.
2. On the Inputs tab, tick Enable on a free input, name it (EGT, for example) and set Type to the 5 volt sensor type.
3. On the Configure tab, set a custom 5 V calibration. Voltages go along the bottom and values along the top. Put every point on one straight line: °F = 32 + 360 × volts for an EG5 (4.80 V = 1760 °F), or 32 + 450 × volts for an EG12 (5.00 V = 2282 °F). Set Units to °F and Format to the decimals you want.
4. Open the Pin Map, choose View Inputs, and drag your input from Unassigned Inputs onto the pin you wired. It has to be a pin with the same symbol.
5. Save and send the configuration to the ECU. Cycle the key if the software shows Ignition Cycling Required Before Start.

Don't copy the scaling from Holley's own analog EGT sensor. That one reads 0.5 V = 32 °F; an EG reads 0.000 V = 32 °F.

On a Super Sniper, the same calibration goes in SENSORS → Custom Sensors 1-3 in the Sniper EFI PC software. Sensor settings can't be edited while online, so change them offline, send them, then cycle the key.

A dash means past that model's range.

04See it and log it

• Terminator X handheld: MONITOR for gauges, LOGGING for logs.
• HP and Dominator: the Datalog menu.
• Super Sniper: any gauge on the GAUGE PANEL can show the channel.

05Optional: warnings

The Sensor Min's and Max's on the Configure tab set caution and warning limits. They only act through the switched caution, timing and PC warning outputs, so tick the ones you want.

1. On an HP or Dominator, an I/O output can use the EGT as a Sensor Input Trigger for a warning light.
2. On an HP or Dominator, Advanced Tuning tables can use the EGT input for an axis or for activation, if you want the ECU to act on it.

On a Sniper, Sensor Warnings are display-only.

Troubleshooting

The input shows LOW Err

Holley shows LOW Err for an unplugged, open or shorted 0 – 5 V sensor, so check the wiring first. An EG sits close to 0 V on a cold engine; if the wiring checks out, see whether the error clears once the exhaust is warm.

It reads nonsense after loading someone else's tune

The pin map came with the tune. Check the input is still mapped to the pin you wired.

It reads near full scale, or shows an error, on a cold engine

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

The reading falls as the exhaust heats up

The probe's leads are reversed at the splices. A reversed probe reads right at room temperature, then falls toward 0 °C as its tip heats. Swap the probe's two leads.

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 the sensor ground.

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.