P0502 Help!!

[gtstorey]

Neither the ECM or the scan tool is going to measure the resistance. The set for that code is the transmission output speed is 58rpm or less for 5 seconds .

[jstatham]

It kicks about 2 minutes into the evap test when it has you idle at 1800-2000 rpm’s. The speed of the Transmission and rpm’s should be zero I guess. When you drive it the speed sensors works fine. Strange

[gtstorey]

Try the idle without running the test and see if it throws the code.

[gtstorey]

And watch live data for the output speed.

[jstatham]

I have and it all works fine. I drove for 50+ miles. As soon as I hook up the Tech2 and run evap test 2 minutes into it P0502. I will try it again tomorrow.

[Mouse330]

I think you have proven that there is no issues with the VSS, Circuits etc....Looks to me like a compatibility issue, This tech2 vxdiag setup is that the windows based program? I'm not familiar but I don't think its the correct protocol. The GM Tech2 was not compatible with the Fbodys, I think you need to find a shop or someone that has a Autel or Snap-on scanner and have them run the EVAP service bay test.

[jstatham]

I put the new vss sensor back in it and cleared the codes. I then cranked it up and idled at 2000 rpm’s for 4-5 minutes and no codes. I drove it around the block and all the monitors reset except for O2 and evap. I watched the live data and the speed sensor is working fine. So now I am back to needing to run the service bay evap test. I am trying to find someone with an Altel scanner instead of the tech2 and see what happens. I am still trying to wrap my head around why all the new sensors are registering 1800-1900 ohms out of the box and the spec is 1300-1500. I thought about testing the OHMs on a new AC delco one just out of curiosity. Anyone have any thoughts.

[jstatham]

Originally Posted by Mouse330

I think you have proven that there is no issues with the VSS, Circuits etc....Looks to me like a compatibility issue, This tech2 vxdiag setup is that the windows based program? I'm not familiar but I don't think its the correct protocol. The GM Tech2 was not compatible with the Fbodys, I think you need to find a shop or someone that has a Autel or Snap-on scanner and have them run the EVAP service bay test.

Here is what I have and it has worked great for 3 years and I got the test to pass fine about a week ago. At this point I agree at snap on or Autel is the next step just to eliminate the interface.

VXDIAG VCX Nano Compatible for GM/OPEL with GDS2 and Tech2WIN System Diagnostic Tool https://a.co/d/e7Zm9In

[gtstorey]

I have the same tech2 setup but never tried or needed it on the Camaro. But who knows what might be going on in reversed engineering program. If you have tried the same idle up steps without it connected and no problem, that is about the only variable. Have you watched live data to see what the shaft rpm is in that scenario and see if it is running real close to 58rpm.

[Mouse330]

Originally Posted by gtstorey

Neither the ECM or the scan tool is going to measure the resistance. The set for that code is the transmission output speed is 58rpm or less for 5 seconds .

The ECM does check for short to ground, open/high resistance and shorts to voltage, This code will set on the VSS low/high signal circuits for these conditions.

[jstatham]

Ok here is the latest. I borrowed an Autel Scanner and ran the evap test and about 2 minutes in to the test it failed and of course kicked the P0502. UGHH. I have a buddy who is a GM tech said when they get crazy problems like this they disconnect the battery let it sit for a while and then touch the positive and negative terminal for a minute. He said that does a reboot of all the modules. I did this then drove it around the block and have everything set but the evap. I have to wait 17 hrs to run the evap test and fingers crossed this did something. I am not very optimistic. The good thing is I know my scanner is good.

[gtstorey]

Originally Posted by Mouse330

The ECM does check for short to ground, open/high resistance and shorts to voltage, This code will set on the VSS low/high signal circuits for these conditions.

What I remember from the service manual is those other conditions set to other codes besides the p0502. The only condition for setting p0502 listed (this from 2010 service manual, others could be different) was the less than 58 rpm.

[Mouse330]

That was going to be my next suggestion to you was the battery disconnect and connect the Pos. and Neg. together. I've done that quite often when readiness monitors wont set.

[gtstorey]

Originally Posted by jstatham

Ok here is the latest. I borrowed an Autel Scanner and ran the evap test and about 2 minutes in to the test it failed and of course kicked the P0502. UGHH. I have a buddy who is a GM tech said when they get crazy problems like this they disconnect the battery let it sit for a while and then touch the positive and negative terminal for a minute. He said that does a reboot of all the modules. I did this then drove it around the block and have everything set but the evap. I have to wait 17 hrs to run the evap test and fingers crossed this did something. I am not very optimistic. The good thing is I know my scanner is good.

Have you reviewed the saved data that recorded when the p0502 set. It might help to know if the vss rpm registered below 58rpm.