Crap, Trans problems

[nightrunner84]

I have a 89 E350 Ambulance that the over drive light just came on. It's not the normal green that is is when I push the button to kill the high gear, this time is amber. It won't go into first, and I have to pull it down into second, or it tires to start off in third. Overdrive is totally inop. Got out the Snap-on brick and it won't connect to the TECA, neither can i pull codes manually with a meter. Reverse works fine, so I think that means first gear is still there. Being that I'm not exactly a trans guy(very poor actually), I've decided to come to you guys. Anyone have any ideas?

 

[trackspeeder]

Sounds like the TCM isn't getting power. Check the relay and wiring for damage or corrosion.

 

[nightrunner84]

Sounds like the TCM isn't getting power. Check the relay and wiring for damage or corrosion.

Wouldn't happen to know where they put the TCM would you?

 

[trackspeeder]

I believe it is located someplace on the passenger side (fire wall) of the vehicle.
I have to guess because its a van.

 

[icanfixall]

The E4OD trans needs a good signal from the tach and the injecter pump tps. The switch on the drivers side of the pump needs to be replaced around 50,000 to 75,000 miles. Its nothing more than a pionter rubbing across some wires like an old heater reostat. The voltage its set for is between .96 and 1.2 volts are idel with ingine off but ignition switch turned on. If you have a bad tach signal this will cause the limp home mode that your in now.... Don't run the truck too long because it will damage the trans. On the trucks the computer that controls the trans is located behind the drivers side floor kick panel. Its tuff to get at because of the parking barke in the way....

 

[GenLightening]

I think the vans have the TCM under the dash, more in the middle.

 

[nightrunner84]

The E4OD trans needs a good signal from the tach and the injecter pump tps. The switch on the drivers side of the pump needs to be replaced around 50,000 to 75,000 miles. Its nothing more than a pionter rubbing across some wires like an old heater reostat. The voltage its set for is between .96 and 1.2 volts are idel with ingine off but ignition switch turned on. If you have a bad tach signal this will cause the limp home mode that your in now.... Don't run the truck too long because it will damage the trans. On the trucks the computer that controls the trans is located behind the drivers side floor kick panel. Its tuff to get at because of the parking barke in the way....

Nice! I know how to check the TPS, but how do you check the tach? I assume it sends out a pulse that can be seen on a scope? Is this what limp home mode is?

 

[icanfixall]

Limp home mode is what happens when several things go wrong. Loosing the tach signal is one. A faulty tps is another... Too much voltage going into the cpu from the tps is another. If the cpu sees 5 volts it shuts down and your in limp home mode. LHM is a safety thing. It allows you to get off the road to safety but... You need to find out the whys this is happening... If you continue to drive the trans is shifting really hard and not all the gears are available to you. I was under the impression only 2nd and reverse were available. Could be wrong on that or thinking about other problems with the trans. A scope will tell you if the tps is *****. You connect it and then slowly open the throttle. Key on but not engine running. Any electrical drop of signal tells you the tps is bad. They need to send out a continuous signal. Any interuption and the LHM is in play.