service brake system and tranny problem

[Newman1415]

I have been having problems with my rear wheel speed sensor on my 04 LB7 with 134,000km , once i reach 80km/h it brings up service brakes system, the abs and park brake light comes on and the truck shakes lightly for a second. it is bringing up trouble codes CO55, PO735, P0700 AND P01621 I did some towing the other day and my tranny made a hard downshift going up a hill, my check engine light came on and the message screen said Range Shift Inhibited thats when i first got the p0700 and 735. I think that it did this because of my speed sensor confusing something under the hood. The truck does not have a tuner, i have no idea whether the guy before i bought it had one and hurt this tranny with it .But not sure, i also heard that having one tire on the truck that is more dull than others really sets off the speed sensors and one of mine is more dull. Where is the speed sensor located in the rear end , and can you think of any reasons it is doing this to me.

[mbottomly]

I am not certain about your specific problem, but in my experience, the electronics(sensors, harnesses, dash instruments, heater, A/C etc..) is usually the first part of a gm to have problems. Sometimes shorts will show up at higher or lower temps, the towing could potentially have caused the symptoms.

[ob_1jr]

I am willing to bet that the previous owner had a programmer on your truck and beat the snot out of it. When was the last time you changed your spin-on filter on the tranny? how are you reading your codes? It is possible that if the previous owner did use a programmer on your truck they could have not programmed it back to stock.

[IdahoRob]

Check your speed sensors. You have an output and engine speed sensor. Output is on the transfer case, and the engine sensor is on the bell housing. Easiest way is to follow the wires to the connectors and give them a pull, making sure they are seated. Sounds like one of your speed sensors if not working properly.

[Supper]

Originally Posted by Newman1415

message screen said Range Shift Inhibited

NSBU Switch mine did the "Range Shift Inhibited" not too long ago, NSBU cleared it right up.

[Newman1415]

i bet the previous owner had a programmer too, the dealer said they changed all filters and fluids, so i have never replaced that filter. I just picked it up less than a month ago. Im raeding my codes with the GM tech 2, a guy that works at GM is doing that for me. We think its the speed sensors, but im looking on this these forums and guys saying the P0735 is a dirty trouble code, its the C3 clutch discs that are damaged in the allison and that i better save for a tranny rebuild. What do you think.

[IdahoRob]

Try the easy stuff first. Speed sensor and good point on the nsbu, but I think the 04 had the updated one from the factory IIRC. Doesn't mean it not bad though, but not sure if it would set off the ABS.

The ABS light is what is leaning me in the speed sensor direction.

[gr8shot]

isn't there usually codes that are specifically for the transmission when it gets slipped? I've seen a lot of posts where people have DTC's that are related to the tranny and it usually has to do with it going into limp. I agree with Rob, he knows all!!! do the cheap stuff first, anything is cheaper than a transmission!!

[Newman1415]

Yea your right im going to start with sensors and work my way to the tranny, hope i dont need to go that far, but is it not bad when my truck downshifted hard when towing? and brought up that p0735 code, or is it just my brake sensor or speed sensors throwing the tranny off?

[IdahoRob]

If the speed sensor is not reading right, then the TCM/ECM will not know what speed you are running and will make the tranny do all sorts of wierd stuff.

Your tranny may be hurt also(lets not assume), but baby steps first.