I have a 02 Mit Diamante that has had a heater core leaking problem A few days ago my tranny seems to be missing the lower gears and jumping directly to 3rd gear. Through research and asking around this seems to be a VERY common problem. It is indicated that the heater core has leaked down onto my ECU and/or transmission relays and has caused the electronic transmission control to act up.

Indications: When putting car into gear and hitting gas, you have to reve it up to about 3000 rpm's before the tranny kicks in, and it goes in and out. Same with reverse, so on and so forth. The dash light is flashing between nuetral and drive and the check engine light came on at the exact time this started happening.

I have changed out the transmission fluid within the last day and the problem still exists. I have been advised that it is NOT the transmission.

Anybody got any other information? Has anybody had or have the same problem??

PLEASE HELP ME...SINGLE MOM IN NEED OF HER CAR.

Kimberly

HI and welcome to the forum

the ECU is above the passengerside kick panel wall about glovebox height

the TCU is located on the floor behind the radio under the carpet

the auto problem if it is in fail safe may well be the TCU(transmission coumputer unit )

if you need a replacement unit it is cheaper to buy it from a wrecker or a
""you pull it ""

Well the 3rd gear issue is in a way a fail safe but its nor computer , its just a manufacturer build design. In teh valve body fluid is always flow to teh 3rd gear clutch set unless the 1-2,2-3 or 3-4 solenoids are powering them with the line pressure valve. if there is no lower gear solenoid interaction flow will just flow to 3rd gear while engaged in third via the selector valve. But yes water damage will cause this when the TCM is damaged.

don't worry too much about your car I just fixed the same exact problem with the whole neutral light flashing, starting in third gear... the works. its just that when your heater core starts to leak (its actaully just a bad o-ring in your heater core, most likely not the heater core itself. the heater core in the diamante is very reliable conterary to popular belief) it will leak down behind the dash and under the carpet where your relay for your TCU is and it screws it up. a new TCM is like 30 bucks brought my to a dealer and and got the diagnostics, labor, tax and part for like 150... kinda ripped off but I didn't know what it was back then.