RLYSLO

Hi all...

I have a question for you all..... a couple months ago, someone installed some 3.42 gears for me upgrading from my 3.15 stock ones. I made a slightly long trip before having the car tuned (1.5 hours there and 1.5 hours back), and as I got close to home, got the p1870 and the transmission went into limp mode. So after reading up on here, I had hope this would be resolved with a tune. I took it to a shop and got it tuned via hp tuners. I know he inputted the gear ratio as 3.42 and also adjusted the shift points some as well as tuning for better HP. This was about 2-3 weeks ago. So on tuesday I took the car back out on the same drive (1.5 hours there and 1.5 hours back) and about the same place, again the car threw the p1870 code and went into limp mode.

I made this trip a couple times before changing the gears and did not have this issue, so I'm thinking it's not mechanical (but I guess there is a possibility it might be).

I have read on here about a tcc slip table. Is that different than simply entering the new ratio in and adjusting the shift times on hp tuners? Is there maybe something my tuner might have missed? I'm just trying to see if there is anything else it could be before breaking into it mechanically.. especially since this started after the gear change.

any help would be greatly appreciated as I am not too knowledgeable on all of this.

Keith

gojo

You have a PM.

RLYSLO

replied.. thanks!

tblu92

The TCC slip table is really called the PWM table (pulse width modulation)--you need to set the minimum to 90 across the entire table and the max to 100--It is in the TCC files

Also--when installing a different rear end in a C5--it is NOT neccessary to make any speedo adjustments--The pick up for the speedo is on the output of the transaxle and not on the output of the trans--Some people still change the diff ratio in the tables but it is not required--I have found that you are less likely to get codes if you leave all the diff tables stock--even if you've changed it-The only time you need to make spedo corrections on a C5 is if you change tire sizes--but again--not diff ratios

RLYSLO

thanks for the great info!

gojo

That's true for a manual trans. He has an A4. The gear ratio must be inputted. If he doesn't make the gear ratio change in the tables, the trans will not shift correctly and will assume there is slippage.
100 and 90 are extreme. 99 and 50 are plenty and still allow the test to run for true slippage,

tblu92

Well on my own personal '98 Auto--I changed from a 3.15 to a 3.42 and installed a 2600 stall--I did not touch ANY of the speedo or axle tables--- The only changes that were made were stall converter and trans related--looking at the speedo and axle files--there are changes to be made only if changing between an A4 and a manual--
Also--when reading the post it seems he changed the speedo/axle tables-And is having codes and problems--My point exactly--that they need to be left alone--As far as the PWM table--Most transmission shops when doing a rebuild , mecahanically disable this feature anyway--making it 100/100 --So reducing its function via the computer does the same thing and is a welcome mod to eliminate TCC slippage and slow engagement at lock-up

gojo

If you do 100/100 you're elminating the slip test entirely. I prefer to have it still run. I suspect that many(don't know about most)tuners take the easy way.

Her's what GM says:
from GMTC P1870 Transmission Component Slipping

Range
Gear Shift Solenoid TCC Solenoid TCC PWM Solenoid 2-4 Band Forward Clutch 3-4 Clutch Torque Converter Clutch
1-2 2-3
Overdrive 4th ON OFF ON 90% (ON) Applied Applied Applied Applied

Circuit Description
The Powertrain Control Module (PCM) monitors the difference between engine speed and transmission output speed. In D3 drive range with the TCC engaged, the engine speed should closely match the transmission output speed. In D4 drive range, with the TCC engaged, the TCC slip speed should be -20 to +30 RPM. The table above indicates solenoid states and transmission components that apply, during 4th gear, with the TCC commanded ON.

tblu92

It's all a matter of preference--some like a firm crisp lock-up--others prefer a slower soft one----From what we were told at EFILIVE training--the reason GM made all the shifts lazy and the TCC lock-up soft was due to their market research and they found that women now drive close to 50% of their trucks and SUV's--And they prefer soft "seamless" shifts--It's not for lonegivity as a soft seamless shift is achieved by slipping the clutches by slowing down the shift times---Same with the TCC lock-up--slower pressure application rates make it seamless but slip---My preference is to have a snappy shift time and a firm TCC lock-up--which is best for performance and trans life as well as keeping the fluid temps down

Mike Mercury

huh

gojo

Mike,
If he means that high performance tranny's then 100/100 is correct.
Joe

Mike Mercury

help me here then. How can a mechanical change stop the PCM from comparing the RPM versus MPH... for setting the P1870 code ?

only way I know to do that is by software changes.

gojo

I agree with what your saying, Mike, how else could the PCM know the tranny is slipping if it did not have an expected number of pulses vs actual? I'm only referring to the point that built tranny's set PWM to 100/100, because the converter clutches can't take going on and off in performance situations.

It just occurred to me that I didn't fully answer you. P1870 is also caused by TC clutches slipping and also by the PWM solenoid going bad and causing slipping.

4L60E P1870 After Ring and Pinion Replacement #PI00807 - (Feb 12, 2003)4L60E P1870 After Ring and Pinion Replacement.
When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.
Condition/Concern:
The 4L60E automatic transmission may experience a condition of DTC P1870 after the installation of an incorrect ring and pinion gear ratio.
The P1870 DTC will set on a Corvette after installing the incorrect ring and pinion because the Output Speed Sensor (OSS) is calculated off the ring gear in the axle and not the output shaft of the transmission typical of other applications.

nj02vette

Just wanted to mention that 3.15->3.42 ratio change is the smallest change you can make doing a gear swap and the ONLY change where you don't have to change tables.