: Transmission Attacked: ECM Accused of Attempted Murder



cmgrafmc
05-14-05, 03:38 AM
I thought that might get your attention.

I had all the sensors checked, everything registers fine, voltages are normal. So I pulled the fuse for the ECM and now I'm not having that problem with my transmission. It was shifting into 1st late while slowing, causing the engine to lug and pull down just before stopping.

So the problem is definitely electrical and related to the ECM. Though everything tests fine I can only assume the ECM is malfunctioning somehow or maybe something is wrong with the PROM. No clue but that's about all I can think of. Mileage is still terrible, too.

N0DIH
05-14-05, 01:53 PM
TCC Solenoid bad? Check for TCC and VCC on the FWD and 4.9L forums. They have this problem a lot.

cmgrafmc
05-14-05, 04:28 PM
The solenoid is fine, it's been replaced twice. Once to solve an actual solenoid problem and again when this new problem popped up. I've checked other forums as well, including the ones you suggested, even though those are for a different engine and transmission.

N0DIH
05-15-05, 01:38 AM
You can unplug the trans and see what changes, at least it will be drivable.

BUT, the lack of lockup on the ultra low gears that you likely have (2.56) will cause the converter to stall at cruise, so you can't drive like that daily unless you nix using OD or trigger manual lockup. Trans will overheat quickly when slipping with that low of gearing when in OD and no lockup.

On the ALDL the 85 G body cars used pins A & F for TCC diagnosis. Not sure what Cadillac did, but I would be willing to bet it is. Stick a DMM into those 2 pins. (Top row, outer pins) Voltage will go low when locked up, high when not, and low when brakes applied, and high when in 3rd gear or higher but not ECM commanded to lockup, if memory serves me right.

Grounding locks the converter, not going to +12v. Pin F is the wire to the trans and to the ECM, so it will show +12v when trans is in 3rd or 4th, low (near ground or ground) if brakes applied as it loses it's +12v from the brake circuit, and low when locked, as ECM is now grounding that line.

Follow me?

Hope so! You can trigger a manual lockup by grounding pin F anytime that trans is in 3rd or 4th. Basically voltage has to be present to complete the ckt. You are reading it THROUGH the TCC solenoid. So the ECM will ground the line completing the ckt.