Where does the trip computer get its info from

skloon · Post by **skloon** » 29 Nov 2015, 19:02

Just finished an RN/Manual swap and see that my trip computer and clock have taken a vacation without me- it doesn't matter which ECU I use, does it get information from the TCU >

Post by **cvergi01** » 29 Nov 2015, 20:13

Yup, from the speed sensor at the final drive is what calculates the miles accumulated. It sends the info to the TCM, which stores it and sends lots of info to the ECM to calculate and play with in regards to timing/fuel trim. The TCM holds the necessary info regarding the transmission/driveline usage to determine torque lockup and other things based on your driving style in the same way that an ECU holds onto the fuel trims and such.

In this way the TCM is the master cylinder and the ECM is the slave cylinder (if they stored info to adjust your pedal response pressure).

I think.

Post by **cvergi01** » 29 Nov 2015, 20:14

WHOAH....That was confusing.

Washington.

Post by **abscate** » 29 Nov 2015, 20:16

Hmmm ...my 1999 has no TCM since it's a manual but trip odometer works fine. My guess is ECU gets info from wheel sensors directly on both cars

skloon · Post by **skloon** » 29 Nov 2015, 20:29

I am getting my speed signal from the abs as my transmission is out of a 2004 s60 and the car is a 94

Azik09 · Post by **Azik09** » 30 Nov 2015, 06:32

TCU and gearbox have not any relation to trip computer. Speed signal is sending by ABS module. Or by separate speed sensor, if your car is pre-1994 Volvo 850.

skloon · Post by **skloon** » 30 Nov 2015, 12:28

it is a 94 turbo, the speedometer works- maybe Ill go with the obvious and check fuses

Post by **pkc303** » 23 Feb 2016, 06:29

Well, that explains why the fuel trim was not showing a change, the cruise control not working, and the odometer not moving despite me changing the broken gears. I was able to test the odometer, and it worked with 12v pulse applied. Thanks for the information about the speed sensor for the 1995 850 T5-R