Hi all,

This is my first thread here. I bought this grandprix with a faulty transmission with the following simptoms:
1. Transmission slipping badly in all gears including reverse.
2. Transmission seems to start with second gear (The second gear start switch is off)
3. Speed gauge always shows about 20Kmh more. Even when in complete stop it shows a speed of 20Kmh

I connected OBDII and got the following codes:
1. DTC P0756 2-3 (B) Shift Solenoid
2. DTC O1870 Transmission Component Slipping

After reading a lot in the internet regarding those codes, I looked around I noticed that there is no vacuume hose conneted to the transmission (A metal hose poping from the transmissions upper side below the air filter)

I need you help regarding:
1. Can the missing vacuume hose caused this problems?
2. Where that hose should be connected to?
3. If it is not the hose will replacing the B solenoid solve the problem?

Thanks in advance
Yaron

The hose controls how firm shifts are. With no hose, it should be shifting hard all the time. I'm not sure of other side effects, but you can at least run a hose from it to the intake manifold. The one on the car I'm working on has it running straight up and into the crook of the upper intake manifold to the left of the throttle body.

If the tranny is slipping, your clutch plates are probably toast. The solenoid could have been replaced by ripping the side of the tranny off, but at this point it looks like you'll need a full rebuild.

If the vacuum is not connected it will cause some issues not sure exactly what all problems it could cause but it is a factor.

x2 with Rook, sounds like the clutch plates are done. That entails pretty much fully rebuilding the transmission. And 'mad props' as they say in the hood lol for ACTUALLY researching for an answer before just posting up 'my trans doesn't work that great, whats wrong?" as alot of ppl do (not necessarily this forum).

and about the 20 km/h thing, as u start moving, say going about 10 km/h does it move up to 30? or does it stay at 20 until u actually go above 20 km/h? it could be the needle in ur cluster, try pushing it down. I doubt its ur actual speedo cause it probobly wouldn't move at any speed at all.

the vacuum modulator is necessary fo proper funtioning of the 4T60E ,locate the modulator and run a vacuum line to the TB unless someone has swapped in a 4T65E but then shifting will not work properly because the PCM is not programmed to respond ,anyway it sounds like the damage is already done .Chico(pops)

Thank you all for the info I will consider replacing the tranny or rebuilt it.

to r.s.hutchinson the speedo is 20 if I am in complete stop, 30 if I am in 20, 100 if I am in 80, etc.

then ur speedo works, its ur cluster. remove the front plastic piece of ur cluster and push the needle down to 0.

do you mean 4t60 and not 4t60e? how would vacuum affect the 4t60e? I can see it affecting the 4t60 but not 4t60e.

The 4t60e has electronics, but it still uses a modulator valve.

i thought the 4t60e was 'fully electronic'...not saying ur wrong, just that to me if it requires that modulator it doesn't really seem 'fully' electronic. learn something everyday.