Why log gearbox line pressure?
An automatic transmission clamps its clutch packs and bands with hydraulic pressure from its pump. If that pressure sags from a worn pump, a stuck valve, low fluid or a leaking seal, the clutches start to slip, heat builds and the damage snowballs. A line pressure sensor lets the Elite ECU watch that pressure, log it alongside rpm, gear and throttle, and warn you or protect the drivetrain if it goes out of range.
These are powered sensors with three wires: 5 V supply, signal back to the ECU and signal ground. On an Elite, the sensor's job is monitoring and protection. It doesn't control line pressure itself.
Wiring tab
Pick the input
Put the signal on an AVI (analog voltage input). That's what the sensor is designed for and what gives you a clean reading. If you've run out of AVIs, an SPI (synchronized pulsed input) can read it as a fallback. When using an SPI, set Sensor Type to Hall Effect, which is the correct choice for any analog signal on these inputs.
Pull up: usually off
Each input type has an optional pull up to 5 V: a 1k resistor on an AVI, a weaker 10k on an SPI. Pull ups are for two-wire sensors like temperature senders that don't make their own voltage. A three-wire pressure sensor powers itself from the 5 V supply and drives its own signal, so the pull up should be disabled. It should also stay off if the sensor is shared with a factory ECU in a piggyback setup, because the other ECU normally provides any pull up the circuit needs.
Calibration tab
The ECU has to know how to turn volts into pressure. ESP ships with a set of sensor calibrations you can load with the open icon at the top left of the tab. If your sensor isn't there, build a custom calibration from the manufacturer's voltage and pressure data, then save it with the disk icon next to the open icon so you can reuse it on the next car.
Before you trust any reading, compare it with a mechanical gauge on the test port at idle and at a raised rpm. A wrong calibration will make healthy pressure look low, or hide a real problem.
Display tab
- Warning Minimum: below this pressure, anything in ESP showing line pressure flashes red.
- Warning Maximum: above this pressure, the same red warning shows for high pressure.
These are visual only. They make a problem obvious on the laptop but don't do anything to the engine.
Diagnostics tab
This is where the sensor becomes a safety feature. Each check is off by default. When enabled, it sets a trouble code, and if engine protection is active you can give each code a DTC severity level so the ECU reacts to it.
| Setting | Code | What it catches | Our advice |
|---|---|---|---|
| Raw Min | P0842 | Signal voltage below a set level, meaning a short to ground or a broken wire | Set just below the lowest voltage the sensor ever outputs in normal use |
| Raw Max | P0843 | Signal voltage above a set level, meaning a short to supply or an open ground | Set just above the highest normal voltage |
| Operating Min | P0841 | Real pressure lower than it should be | Base it on logged pressure from a healthy transmission, with some margin |
| Operating Max | P0844 | Real pressure higher than it should be | Same approach: log first, then set |
The Raw limits are about wiring faults and the Operating limits are about the transmission. Keep them separate in your head. A sensor with a broken signal wire can read zero pressure, and you don't want that treated as a transmission failure without knowing why. See the DTC index for the full code list.
Setting it up, step by step
- Wire 5 V, signal and signal ground to the sensor, with the signal on a free AVI.
- Assign the input on the Wiring tab and make sure the pull up is off.
- Load or create the calibration on the Calibration tab.
- Compare the ESP reading with a mechanical gauge.
- Drive the car and log line pressure in every gear, cold and hot.
- Use that log to set the warning and diagnostics limits, then enable protection if you want it.
Troubleshooting
| Symptom | Usually |
|---|---|
| Reading pinned at maximum | Broken signal wire with the pull up on, open sensor ground, or signal shorted to 5 V |
| Reading stuck at zero | No 5 V supply, broken signal wire, or input assigned to the wrong pin |
| Reading steady but wrong | Calibration doesn't match the sensor |
| Noisy, jumping reading | Poor signal ground, or the sensor ground shared with a high current device |
Related pages
If you're controlling line pressure on a Nexus rather than just monitoring it, see line pressure control and transmission line pressure. Other Elite transmission pages include the trans-brake and the Ford Falcon 6-speed automatic.
FAQ
Does the Elite control line pressure with this sensor?
No. On this page the sensor is for logging, warnings and engine protection.
Should I turn the pull up on for a pressure sensor?
No. Pull ups are for two-wire sensors. A three-wire powered sensor drives its own signal.
