I am stumped on this one... My rover keeps going into limp mode and i can't figure out why. I went to leave the parking lot at work and the trans went into to limp mode. I popped the hood and tightened up the bat. terminals and when i started the truck it was out of limp mode. I then drove about 6 miles, turned the car off and when i went start it up again the limp mode was back. I tried to adjust the cables, but this time no joy. At this point i got the truck to a friends shop and went to wrenching. I took out the XYZ switch and cleaned that out, though it looked brand new. The bat. was a little low, showing only 12.35 volts, so I replaced it. When i went to start it up limp mode was gone, victory was mine, or so I thought. A few hours later I went to test drive it and the limp mode was back on. I figured the code was pending or something, so i took my friends scan tool and cleared the transmission code. I took it for a test drive and everything was fine. I drove it to and from work today and everything was fine. When I went to go buy dog food for the hounds..... limp mode was back on.

There is only one code being thrown and that is P0758 which is shift solenoid B.

If anyone can give me a lead on figuring this out I would be greatly appreciate it.

Thanks

 

Measure battery volts again when at idle, with light and AC and wipers on. Should be 13.2 or better. With just engine running should be 13.8 - 14.4.

 

Go to your local parts store and have them do a free charging system test. As Buzz mentioned you need between 13.8 and 14.4 volts to provide adequate voltage to the tranny computer.

 

Pardon my newb-ness, but what is limp mode? And how do you know if your transmission is in limp mode?

 

You will only be able to drive in 3rd. gear and your M/S lights will come on along with your service engine light.

 

Thanks for the reply folks. I got the alternator tested and the voltage regulator was bad. I should have thought about this when I replaced the bat...
Thanks again for the the help and I will keep you guys posted.

 

Limp mode is when the transmission will go into a mode to just keep the truck going and not self destruct.

It means something has gone wrong and the transmission computer finds the fault not correctable.

I would do as Mike has suggested and check the voltage with high beams on, A/C on.
See if the alternator can keep the voltage of the battery up.

IF your transmission fluid has never been changed, maybe getting in some new fluid
may cause just a bit less friction for solenoid B.

 

Actually, you are in PHX.
That place KILLS the battery.

And maybe kills alternators too.

 

It has to be a bad Alt. It failed the load test that was done at the parts store and for good measure I went home and put a volt meter on it anyway. With the engine at idle with no load I'm at 13.6v. With the lights, A/C, dome lights and radio i am at 13.5v.
I wish it was below 13.2 as buzz and Mike said, but I'm still pretty sure the Alt. is the problem. Perhaps this is why limp mode comes and goes.
When I drove to the part store the limp mode was off and truck was good to go, after i shut it off and restarted it at the store limp mode was back. I have a love hate relationship with my beloved Disco II =)

 

Whoa - no load (engine running 13.6 - that is low end of OK range.

All the stuff on, should be ABOVE 13.2, so your alternator is able to keep up with the load.

We'll have to figure maybe your meter is a little off. The parts store computerized tester is usally pretty good.

Now the wiring from battery to transmission computer includes the frame of the truck, so bad grounds can do this. You can attach a jumper cable to negative battery post and engine to see if volts come up some.