I'm running a TCU V2 (firmware 10.75) on a ZF 8HP50, connected to a Link G4X via CAN (Type CAR = 6, custom ECU, base RX ID 1536 / TX ID 1600).
Problem: The "Transmission Oil Temp" received over CAN (TX stream BaseTX+2, byte 3) reads noticeably higher than the "Oil Temp (C)" shown in TunerPro over serial, and the gap grows as the gearbox warms up - e.g. TunerPro shows about 61 C while the CAN side shows around 80 C. The CAN raw byte appears to rise roughly 1.5x faster than the serial value.
What I've already checked:
- The ADX "Oil Temp (C)" uses X - 40, and the CAN spec is also unsigned8, 1 C/bit, offset -40 - the conversions are identical on both sides, so the raw values themselves must differ.
- Other channels on the same CAN stream (gear, torque, speed) decode correctly in the Link.
- Are the serial "Oil Temp (C)" and the CAN "Transmission Oil Temp" taken from the same internal variable? Or does the CAN value use a different source (e.g. a calculated clutch/friction temperature, or a Fahrenheit-scaled value)?
- Which of the two should I trust as the actual sump oil temperature?
- The 10.77 changelog mentions "fixed gearbox temp in Jeep (can type 80)". Do 10.77 or 10.78 also change the oil temp sent on the standard TCU CAN stream (type 6)?