vcarter911

Where to start... I picked up a 97 A8 4.2 a few weeks ago for a great price where the tranny was stuck in "limp mode". As I've owned audi and vw before and have delt with this sort of thing, I took the car without hesitation. I got it home, hooked it up to the VAG and got the code 17114 (P0730). This relates to either ATF quality/level, input speed sensor or the output speed sensor. I did a fluid/filter change and no change. I then looked at measuing block 001 in the measurments to view the sensor readings. The engine RPM and the input sensor readings matched perfectly, however the output sensor reading was at 0 RPM's regardless of gear selector position. I then started trouble shooting that issue. I replaced the sensor and no change. I bench tested the old sensor afterwards and everthing tested fine there. the next step was testing continuity between the sensor and the TCM. I found that wend I pulled a little on the sensor side of the wire. it broke continuity to the TCM. I then ran in new wire and spliced it into the TCM unit. Conection to the TCM tested good so I thought my problem was fixed. I started the car up and to my dismay, Measruring block 1/3 still read 0 RPM's and the car "clunked" back into limp mode. I'm at the end of my rope, and need help getting this fixed. MP4.2, I've read your posting over in the A6 side and that helped, or so I thought. Is there anyway that the TCM could be bad, and if so, how would I test that with the multimeter (setting?)? Any insite on this issue would be appreciated.

icsamerica

The output sensor would provide a reading only when the car is moving. Did you test it when the car is moving? You message didnt mention any reoad test data.

I understand that the error your getting is "inccorect gear ratio". The transmission compairs the input RPM against the output RPM and factors in what gear is selected. If the transmission slips, the trans goes into limp mode becasue the values are off the table. If the limp mode happens in the drive way without the car moving then I think you've got a chance. If limp mode occurs while driving then a clutch is probably worn out and slipping. It would help if you could describe the exact circumstances of the road test and explain exactly when the car goes into limp mode.

You're not going to be able to test the TCM with a multimeter. Consider installing your TCM in a known working car and see if the problem moves or bite the bullet and get a new TCM from the dealer or junk yard.

vcarter911

The car drops into Limp mode as soon as I put it in drive in the driveway. While monitoring the imput and output RPM, the input is running at the same as engine, however the output is running at 0. The is no reading coming from the sendor (output RPM sensor). I know that is will dump into limp mode if they don't match, but this is a step further, and there is no reading period. Its very strange.

tozoM8

Can you drive the car at all?

vcarter911

As soon as I put the car in drive, it clunks into limp mode and then I can drive it around.

Further note - I just tested signal with car running to sensor connector and it tested at 0.02 ohms on the 20m setting on my multimeter. Connection seem to be good, TCM seems to be good, sensor is good, but still no reading. How can this be??

tozoM8

hold the car with the brake, then check it with vag what is the engine speed in D(it should be 700-750rpm) and what is the input speed( should be 0rpm).
vag-com-transmission-measuring blocks-group1-display 1 (engine speed)display 2 (input speed) display 3 (output speed) display 4 (gear engaged). If it is 0rpm, then the tranny is fine mechanically.

icsamerica

If the car is in gear and not moving and the input speed (after the Torque converter) is greater than 0 then something is slipping inside the unit. I'd get a wiring diagram and check for solenoids with improper continuity but if that was the case the TCU would probably pickup the problematic circut and set a code. When the TCU is applies 1st gear and you've got your foot on the brake, the input and output speed should be 0 becasue the input speed is measure at the input shaft after the torque converter.

vcarter911

Here's how it reads when I put it in drive with my foot on the brake. Measuing Block 001-1 (engine RPM) reads between 800 and 1000. 001-2 (input RPM) reads roughly the same (700-900), 001-3 (output RPM) reads 0, and then 001-4 reads 1m (which I think mean mechanical mode). Should I take the valve body out and replace the imput speed sensor?

icsamerica

what is the input reading when it goes in LIMP mode? Im guessing ZERO, if so...that indicates 1st gear in drive is slipping.

vcarter911

I took a Vag-Scope if that would help. It basicly shows that something is slipping, and then when it doens't match, drops into limp mode. The strange thing is it seems to be looking for a gear and the selector is going from to 3, to 4 and then to 5. It then stays in 5. What do you think needs to be done to fix the problem.