Why log coolant pressure?
A healthy cooling system builds pressure predictably as it warms up and holds it. When something goes wrong, pressure usually changes before temperature does. A split hose or a failed water pump seal shows up as pressure falling away. Combustion gas leaking into the coolant shows up as pressure climbing well above normal. The Elite can log the sensor, flash a warning in ESP, and, if you use Engine Protection, act on a fault.
Most coolant pressure sensors are three wire powered sensors: a 5V+ supply, a signal back to the ECU and a signal ground. By default, ESP expects the Haltech 150 psi pressure sensor, such as the 150 PSI TI pressure sensor.
Wiring tab
Choosing an input
Pick the input the sensor's signal wire lands on. An AVI (analog voltage input) is the preferred choice. If you've run out of AVIs, an SPI (synchronized pulsed input) will also do the job.
| Setting | What it does | Our advice |
|---|---|---|
| Coolant Pressure Input | Assigns the pin the sensor is wired to | Use an AVI where you can |
| Pull up (AVI) | Adds a 1k resistor to 5V on the input | Disabled for a powered 3-wire sensor |
| Sensor Type (SPI) | Tells the SPI how to treat the signal | Hall Effect for analog signals like this one |
| Pull up (SPI) | Adds a weak 10k resistor to 5V | Disabled for a powered 3-wire sensor |
Pull ups are for two-wire temperature style sensors that need the ECU to supply a reference. A powered pressure sensor makes its own voltage, so a pull up just skews the reading. The same goes for any sensor that's shared with another ECU, as in a piggyback install. The other ECU already provides whatever pull up is needed, so set the Haltech's to Disabled.
Calibration tab
This is where ESP learns how to convert the sensor's voltage into pressure. Several calibrations come preloaded with ESP, and the Haltech 150 psi sensor is the default. Use the yellow open icon to load a saved calibration, and the blue disk icon to save your own.
If you're using an aftermarket sensor that isn't listed, build a custom calibration from the manufacturer's voltage vs pressure data. Then sanity check it: with the engine cold and the cap loosened, the reading should sit at or very close to zero gauge pressure. If it doesn't, the calibration or the wiring is off.
Display tab
- Warning Minimum: any coolant pressure gauge in ESP flashes red when pressure drops below this value.
- Warning Maximum: the same red flash when pressure rises above this value.
These only affect what you see in the software. They don't protect the engine on their own. Base the limits on what your engine does when it's healthy: log a few drives, note normal hot running pressure and your cap rating, and set the warnings just outside that band.
Diagnostics tab
The diagnostics split into two jobs: spotting a wiring or sensor fault, and spotting a real cooling system problem. All four are disabled by default. When Engine Protection is active, each one can be given a DTC severity so the ECU responds the way you want.
| Check | Trips when | DTC | What it catches |
|---|---|---|---|
| Raw Min | Sensor voltage drops under your set value | P1910 | Shorted or disconnected wiring |
| Raw Max | Sensor voltage goes over your set value | P1911 | Shorted or disconnected wiring |
| Operating Min | Pressure is low while the engine is running and warm (see below) | P0115 | Sudden loss of coolant pressure |
| Operating Max | Pressure goes over your Maximum Pressure | P0128 | A sudden pressure spike |
How Operating Min decides
Low pressure is normal on a cold engine that just started, so Operating Min only triggers when three things are all true at once:
- Coolant pressure is below Minimum Pressure.
- The engine has been running for at least Minimum Running Time.
- Coolant temperature is above Minimum Coolant Temperature.
That combination is what stops false alarms on a cold start while still catching a burst hose on a hot engine.
Worked example
Say your logs show the system settles comfortably above zero once warm, and it never gets near your cap's release pressure. A sensible setup would be:
- Raw Min and Raw Max set just outside the sensor's normal output range, so only a wiring fault trips them.
- Operating Min enabled, with Minimum Coolant Temperature set to a point where the system is always pressurized in your logs, a running time long enough to cover warm up, and Minimum Pressure a margin below your normal hot reading.
- Operating Max enabled, a little above the highest pressure you ever see in normal use, so a head gasket pushing gas into the system gets flagged.
Start with a warning-level severity, drive it for a while, and only move to anything that cuts power once you're confident the limits don't false trigger.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reading pinned high or low | Open or shorted signal, missing 5V supply, or the wrong input selected |
| Reading offset at zero pressure | Wrong calibration loaded, or a pull up left enabled |
| P0115 on cold starts | Minimum Coolant Temperature or Minimum Running Time set too low |
| Pressure climbs steadily under load and doesn't drop | Possible combustion leak into the coolant, check it before driving further |
FAQ
Where should I mount the sensor?
Anywhere that sees true system pressure and stays full of coolant, away from trapped air pockets. Many people tee into a heater line or a spare port on the housing.
Is coolant pressure a replacement for a temperature sensor?
No, it complements it. Keep your coolant temperature sensor for fueling and protection, and add pressure as an early warning. Similar setups work for oil pressure protection and crankcase pressure.
