well here it is i finally got my own 98 4wd blazer after many years. i would love to drive it but the problem is that damn p0740 code.

ok i may sound long winded but i want to make sure i have nailed down the problem.

i did the search for the p0740 code and found kyles curcit drawing and i hooked my the scanner to clear the code watch the brake switch input and see when the code sets. the truck will go into lockup and stay there till i press on the brakes for aout 5 sec,s


so after i got back home thinking my ground would be shorted out. i back probed the feedback wire----tan/blk wire i thought i would not see 12 volts there because of the tcc still being grounded to a short. the brake switch would of told the tcc to unlock and didnt so i threw the code
but i had 12 volts with that reading i was thinking humm the tcc solenoid is not grounded.

i know i dont have a power short because when the scanner is hooked up i can clear the code and lock up will every time work till i hit the brakes i can do this 5+ times in a row.

i also checked my brake input voltage at the vcm and with the key on and the pedal not pressed i have 12 volts and it goes to open when pressed. thats telling me that its getting the open curcit signal to unlock the tcc.

a diffrent test i tried was i ran the blazer on stands to 45mph i back probled the tan/blk wire and grounded the wire out myself. with that being said i can control the tcc not the vcm. every time i grounded the wire it went into lock up and stayed no blown fuse and no smoke. i also did a wiggle test and checked the wireing for any bad spots and did not see any.

so the resion i think the vcm is junk is one of two things
1. the vcm is unable to ground and unground and or is loseing ground
2. the vcm is loseing the feedback signal

if any body has any diffrent idea,s or had the same problem let me know.

thanks...chad

 

bumpp

 

well i ordered a new vcm it will be here tuesday keep u all posted

 

Have you checked over all of the grounds for the PCM & Engine/Transmission?

 

not yet but i probbly shound have done that first. i am just fishing for addvice i still think it,s a vcm issuse though. but a ground check is on my list tomorrow.

 

well all i just installed my new vcm and after a hour long road test all is well and working no codes and runs like a dream....

now all i have o fix is the oil filter lines and i think the remote oil filter housing. happy motoring