1999 C5 Vette 1870 Code

[Blown99]

About 1 year ago, I installed a MagnaCharger Supercharger on my 99 C5 with Automatic Tranny. I noticed a couple of days later that after getting on the interstate, I will drive for about 45 seconds and the TC will fall out of lockup for about 2 sec and then go back into lockup. After an additional 15 sec, the TC will drop out of lockup and will not go back "in" until the ignition is turned off and back on. I get 1870 codes on the dash.

After about 4 months, I ordered a performance transmission and a 2300 rpm stall converter from Level 10 in NJ. The 1870 code and slippage continued. (The valve that causes 1870 code was replaced in the new transmission by Level 10 when it was built). Level 10 calims it was not their problem. During this time, I took the car to a transmission specialist who put a computer on the transmission and he said the transmission was being told to go out of lockup by the PCM. I took the car to a dealer and had the PCM flashed back to factory and then re-applied the program provided by MagaCharger to the car . Magna Charge uses HPTuners to make the modifications to the PCM for their product. (Same results) That transmission went out after about 4 months of use. (pump failure)

Level 10 shipped another transmission and another converter under warranty. The same 1870 code and slippage on the 3rd transmission.

I don't think it is a transmission issue. ???

I use the HPTuners software and found that the tranmission is really slipping. Anywhere between 250 and 800 RPMs. The TCC PWN Duty Cycle is constant at 96.1% and the Pressure control Current is 0.16A.

Is there an adjustmnet I can make with the HPTuners softweare to decrease the slippage to the point where I do not get the 1870 code?

Thanks
Fustrated

[ToplessTexan]

You're saying that you're actually seeing 250-800 RPM of slip (defined as the difference between the measured engine speed and the calculated input shaft speed) under conditions in which the TCC is locked? Or are you saying that the TCC Slip PID is showing values like that in your scanner?

BTW, you can clear DTCs through the DIC while driving if your are coordinated enough.

[Blown99]

I use the HPTuners software which shows the TCC slip RPM.

When the transmission first goes into lockup, the slip is about 200 to 240 rpm's. When it disengages, the slip goes up to an average of 400 rpm and on a hill, will go to 800. According to the GM service manual, the acceptible slip is between -20 and +40 rpm.

I have finally gotten the TCC PWM to give me 100%, but still no change.

Thanks

[ToplessTexan]

First a word warning, I am not HPTuners literate. ;D Have spent some time with the Other Guy's Stuff though...

I'd be inclined to suspect that it's a programming issue, specifically related to gear scaling. You can log all the driveline parameters (e.g. vehicle speed, output shaft speed, input shaft speed, engine speed, gear, and TCC slip speed) and do a little math to convince yourself that scaling has or has not been done correctly. It's slightly more complex for the C5 than the F-body since the VSS signal represents different rotational speeds, output shaft speed for the F and drive axle shaft speed for the Y.

I had to chase through this a while back when the OGS first came out as they weren't convinced it was broken without that data. Your scenario sounds suspiciously similar down to the magnitude of the discrepancy.

A workaround is to relax the P1870 test limits, that -20/+40 RPM you mentioned, so that the test doesn't fail. That is however only a workaround. I believe I had to go all the way to like 800 RPM when I swapped from 3.15 to 3.73. After the software was fixed I went back to stock limits. No further issues and no hardware changes.

[ToplessTexan]

I just realized I have gear swaps on the brain. :-[ I don't think you mentioned a gear swap though, just the converter... Never the less, logging the OBD-II data I mentioned is a good way to determine what your PCM really thinks is going on.

[Casey]

I use the HPTuners software which shows the TCC slip RPM.

When the transmission first goes into lockup, the slip is about 200 to 240 rpm's. When it disengages, the slip goes up to an average of 400 rpm and on a hill, will go to 800. According to the GM service manual, the acceptible slip is between -20 and +40 rpm.

I have finally gotten the TCC PWM to give me 100%, but still no change.

Thanks

You may have 100% TCC duty cycle, but is only a bleed off from the actual line pressure. You may need to increase the force motor current tables on the top end to get more line pressure.

We list the force motor tables from several different GM vehicles, but if you have a modified trans you will need to verify the line pressure vs commanded current with a gauge to make sure you are getting what you ask for on the tables.


The trans mfgr should be able to tell you what the line pressure should (or need to) be vs the force motor milliamps.


Ken

[Blown99]

I agree that it is a programming issue. The problem started when I put the superchager on the car which required the installation of their modified PCM software.

The problem occured with the original tranny and two replacements since and three different Torque Converters.

According to Magnacharger, this is the same program installed in all the C5 conversions and they have not had a problem.

How do you set the slip limits in the software so I cna test to make sure it is the slippage that is setting the code?

Thanks for all the help

[ToplessTexan]

Can't help too much there, again I'm HPT illiterate. Perhaps someone here can comment on what to change to relax the P1870 test limits. Again, these are only relevant when the TCC is supposed to be locked.

Lots of guys have given up and successfully switched to vacuum modulated tranny control. I'm not familiar with whether or not your tranny builder does this, I would assume not. Did they give any programming guidance?

[Casey]

I agree that it is a programming issue. The problem started when I put the superchager on the car which required the installation of their modified PCM software.

The problem occured with the original tranny and two replacements since and three different Torque Converters.

According to Magnacharger, this is the same program installed in all the C5 conversions and they have not had a problem.

How do you set the slip limits in the software so I cna test to make sure it is the slippage that is setting the code?

Thanks for all the help

"Pressure control Current is 0.16A." Which is 160 milliamp

You should be around 98 milliamp to keep the TCC from slipping under load.

The min/max trans slip values are on the TCC diagnostics tab. If you are trying to get rid of the code due to a stall converter during unlock this is the way to do it. If you are trying to get rid of the code because the TCC is slipping under load while locked, bad news..


Ken

[Blown99]

The tranny builer is Level 10 out of New Jersey. They said to use the stock tranny programming.

[ToplessTexan]

Blown99, what kind of TPS does your 160 mA correspond to? It's reasonable for high TPS but not what I'd expect for part throttle which is where I'd expect you to be if you're wrestling with lockup issues.

The smallest current I use is 112 mA and that's way up in both TPS and temp. For most TPS < 80% or so I use currents > 250 mA, in the neighborhood of a little over 1000 mA for real low TPS. I haven't had a peep out of the tranny for nearly three years now.

[Blown99]

I'm sorry, but you will have to explain TPS versus mA. I understan the electrical part, just not the TPS part. I thought the TPS was trottle position sensor.

Blown99

[ToplessTexan]

Yes, TPS = throttle position. The idea is less current yields more pressure and required pressure is a function of throttle position (and to a lesser extent, temperature.) You might see also this thread and think about how you tables compare with those. There's some good info there.

[Blown99]

TP at 72 MPH is about 21%.
The pressure Control Acutal Current as displayed by HPTuners is 0.06A
The Pressure Control Duty Cycle is 5.5%
The TCC PWM Duty Cyle is 100.00%
TCC Slip RPM is 250

It will run like that for abut 45 seconds and then slip out of lockup for about 2 seconds and then go back into lockup. It will stay in lockup the 2nd time for about 10 seconds and then slip out, set the 1870 and not go back into lockup until you cycle power onthe PCM.

[ToplessTexan]

Hmmm... I guess I'd expect to see something in the neighborhood of say 30-35% duty cycle for the pressure control solenoid. Your numbers sound like the PCM is trying to command high line pressure. Can you also see the pressure control solenoid reference current? This should tell you what was commanded, hopefully in agreement with actual. It doesn't tell you why it was commanded though. I'm puzzled by why such high line pressures would be commanded *before* the slip verification steps start.

[ToplessTexan]

Can you also log the TCC Mode parameter? Should be an integer value between 0 and 5. Your numbers above (except the slip) might make sense for mode 4, i.e. in Locked mode after Apply.

You ruled out misfire detection as the source, right? I guess I wouldn't expect your numbers above if that was causing a release, specifically I'd expect the PC duty cycle and current to rise. A trace of these parameters might make it easier to see what's going on.