Intermittent SES

[gbmidyear66]

I have had an intermittent SES problem for a while now - I hoped it would go away when I fixed problem with my throttle body. The throttle body rebuild fixed my Idle problem and IAC - but not my SES problem.

The SES light will go on for about 10 seconds, then go off, only while driving, and only while decellerating (no throttle). It does not show as a trouble code on my Auto-Xray 6000 scanner.

Does anyone have any suggestions / experience on how I might capture what is triggereing the SES? - I was thinking that a PC based scanner might do the trick?

I really hate to admit defeat and have to take it into a professional shop that has the GM scanner tools....

[secondchance]

I have had an intermittent SES problem for a while now - I hoped it would go away when I fixed problem with my throttle body. The throttle body rebuild fixed my Idle problem and IAC - but not my SES problem.

The SES light will go on for about 10 seconds, then go off, only while driving, and only while decellerating (no throttle). It does not show as a trouble code on my Auto-Xray 6000 scanner.

Does anyone have any suggestions / experience on how I might capture what is triggereing the SES? - I was thinking that a PC based scanner might do the trick?

I really hate to admit defeat and have to take it into a professional shop that has the GM scanner tools....

Give it a little time. After going to headers and cat back, my Z threw intermittent code for a few drives then eventually cleared up. I suspect it took a while to relearn.
What you might do is disconnect the battery, let it sit for 20-30 seconds and reconnect. I believe this starts the learning sequence.

[Kevin]

o2 sensors

[A26B]

Anytime an SES occurs, a diagnostic code is stored. Pull the codes & see what you have. Try retreiving them by jumping the pins in the OBD port & read on the inst panel display. Always start with the lowest numerical code first. Fix that & any other numerically higher codes are usually cured. I have no idea why your scanner isn't retreiving the code.

[GOLDCYLON]

Use the paperclip method and pull the codes. They should be stored reguardless if the SES goes out.

However the AutoXray 6000 should see these codes as well. If it isnt im not sure if a Tech1 will see them.

Last intermittent code I use to see once in a while was a Cam Sensor fault

[gbmidyear66]

Thanks for your help guys, I had a brain cramp and forgot all about the paperclip (which is what I used before I got a scanner).

My ECM is showing a code 24 - which I had last year (along with various other idle issues). I did some more digging on code 24, apparently it is set when ... "Vehicle speed was 0 MPH when engine speed was between 900 and 4400 RPM and throttle position angle was less than 2% for 4 seconds" - which is exactly my situ - only happens in motion on decelleration.

The VSS sensor looks painful to replace if you don't have a lift - I may buy the sensor and new tranny fluid and take it to a local shop.

[GOLDCYLON]

Thanks for your help guys, I had a brain cramp and forgot all about the paperclip (which is what I used before I got a scanner).

My ECM is showing a code 24 - which I had last year (along with various other idle issues). I did some more digging on code 24, apparently it is set when ... "Vehicle speed was 0 MPH when engine speed was between 900 and 4400 RPM and throttle position angle was less than 2% for 4 seconds" - which is exactly my situ - only happens in motion on decelleration.

The VSS sensor looks painful to replace if you don't have a lift - I may buy the sensor and new tranny fluid and take it to a local shop.


Im not sure but I think the ZFDOC has a tool to make that a little easier. GC

[gbmidyear66]

Thanks GC - I'll check that out....

[tomtom72]

I thought the VSS's for the '90 Z's were NLA?

I remember awhile back RockAuto had some that they were clearing out of their inventory and I ordered one for my 90. They called me on the phone to tell me that they were sure the VSS they were selling would not work for a 90 Z.

I dropped looking after that and didn't ever verify that they had the story straight.:o

:cheers:
Tom

[gbmidyear66]

Tom

I believe that rumours of the death of the 1990 VSS are just that. I believe the VSS for post-90 cars is different.

I believe the 90 VSS is Standard Motor Products SC6 - just like this one...

http://www.ebay.com/itm/SC6-Speed-Sensor-/260896730243?pt=Motors_Car_Truck_Parts_Accessories&hash=item3cbea82c83&vxp=mtr

If not - I just ordered the wrong part....

Glenn

[c4zr1]

I have the same problem with my 92. The SES light comes on intermittent. I drove it to a Make A Wish car show last Friday. (I do have a Haibeck chip that has my power key on all the time.) No SES light on and my power key light was on when I first left to drive to the show. By the time I drove down to the show about 10 miles the power key light went out and the SES light came on. I thought the chip would keep the power light on all of the time, but no.

When the show was over yesterday afternoon I drove the vehicle home the long way around hoping the SES light would go off. I drove it about 10 miles with the SES on and still no power. I got 2 blocks from home and the SES light went out and I had good power so I took it out for another 6 miles and the SES light never come back on.
Last year I did have my ECM rebuilt. I am thinking about taking out the chip and going back to the stock chip to see if that clears it up.
My next task will be to try and do the paper clip jumper and see what codes I get.

[gbmidyear66]

C4ZR1 - my understanding is that with the factory chip when the SES is activated - the secondaries are deactivated - so your issue with power may be the intermittent SES. Try the paper clip.

[John Boothby]

C4ZR1 - Chances are you have a vacumn leak. If you can check codes, you will know. The vast majority of intermittant SES lights are vac leaks. A vac leak will cause the secondaries to not open, which gives you the light. This includes secondary actuators and/or secondary selonoid. This is my guess.

[tomtom72]

Tom

I believe that rumours of the death of the 1990 VSS are just that. I believe the VSS for post-90 cars is different.

I believe the 90 VSS is Standard Motor Products SC6 - just like this one...

http://www.ebay.com/itm/SC6-Speed-Sensor-/260896730243?pt=Motors_Car_Truck_Parts_Accessories&hash=item3cbea82c83&vxp=mtr

If not - I just ordered the wrong part....

Glenn

Cool! I hope that this one is for our 90's! Let us know how this turns out. Thanks for the link Glenn!:thumbsup:

:cheers:
Tom

[John Boothby]

Rock Auto emphatically told me that the SC8 was the one for the ZR-1. They look the same.

[gbmidyear66]

Rock Auto emphatically told me that the SC8 was the one for the ZR-1. They look the same.

John, I have done some more homework on the issue - you are right (but also hopefully wrong). The 25007308 (SC8) was installed for 90 corvettes with 3.45 rear ends i.e. ZR-1 (and for 3.07 and 3.33 ratios). The 25007224 (SC6) was installed for 90 corvettes with lower rear end ratios (2.59 and 2.73). There were about 5 sources I could find for the 25007308 (including the S.M.P. - SC8) - but they are ALL no longer available.

The SC6 is almost identical to the SC8 - from what I have been able to learn, the ONLY difference is the offset in the shaft that the driven gear mounts on. I understand the SC6 can be used and function 100% identical to SC8 if it is installed 180 degrees rotated (connector lock tab position reversed) to position the gear mounting shaft so that it has the same offset as the SC8.

I will find out soon enough and report.

[John Boothby]

You're right. The SC8 is for the Stock ZR-1 3.45 rear end. I thought that was what you were talking about. Sorry.

My experiance with an intermittant SES light that goes out than comes back on during decel is a vac leak. I have had this happen three times, the first I rebuilt the entire secondary vac system, then a bad out of the box secondary solenoid and finally with a bad out of the box secondary actuator. I rebuilt my entire secondary system and after I replaced the above "New parts" it has performed without a hitch.

From what I understand, when a VSS goes bad the car will not operate above 3K rpm. Just enough to limp home!

[gbmidyear66]

Hi John

I have 4.10,s - but the SC8 is ideally what I need (I have a 43 tooth driven gear on the VSS (which would dictate the SC8)

I "think" I have eliminated all my vac leaks - I have excellent IAC value now - even when engine is hot. I will re-check the secondary system though (it was working fine before I ported the plenum).

For sure my VSS isn't "dead" - car runs generally OK - but there is evidence that it is "flaky" - will know better when I get under there - but am now ready with a new sensor (unless there is something obvious with wiring, gears, etc)

Thanks for your input

Glenn

[John Boothby]

I have a couple spare SC8 (new) if you need one. $50 plus shipping to members of this net.

Did you ever check codes?

[gbmidyear66]

OK Guys, The good news is that I have confirmed you can use the SC6 sensor in the 90.

The SC6 and SC8 are identical - EXCEPT - the slots on the face of the sensor - that the sensor hold down clamp mates to are 180 degrees out of sync (see pics attached). The alignment notch on the face that mates to the transmissison housing for both sensors is in the identical spot (aligned to the electrical connector locking tab). I installed the SC6 with same orientation of the notch that mates to the transmission housing and just filed down the two plastic tabs that the hold down clamp mates to (I guess in theory the sensor could spin - but it is in there pretty tight).

I replaced my transmission fluid - and the shift into 3rd is now much smoother :)

The bad news is - I still have the annoying Code 24 - VSS error - which will come on during deceleration (then clear on the DIC) once the car is warmed up. :cry: I guess I am now looking at possible ECM problem? Any suggestions at this point would be welcome.

[tomtom72]

Glenn, Yes, from the FSM on DTC24 it looks like it could be the ECM or the chip ( MEMCAL or EPROM ). Do you have a stock EPROM that you could swap in just for a test? Maybe someone near you has a spare ECM ( known good ECM ) that they can lend you to just see what happens.

Also, on the shift to 3rd being smoother.....I'm a bit concerned for your clutch hydraulic system's performance. How old are the master & slave? What is the condition of the fluid? Usually balky shifts are a result of system degradation...usually. Check out the link to zfdoc.

http://zfdoc.com/ there is a good Q & A on diagnostics over at Bill's site.:thumbsup:

:cheers:
Tom

[gbmidyear66]

Tom

Good observation on the clutch. I also replaced the clutch fluid while I was down there (color tells me it had been in there a while). This is probably why my shift into third is better. And yes - my slave is wet with fluid on it - looks like it needs to be replaced at some point (its a 91 style - has already been replaced).

I will swap the factory MEMCAL back in - it didn't help any when I was chasing the issue last year (before I fixed the TB and ported the top end).

Looking at the FSM - I think I will try disconnecting the ride control module - it also ties into the VSS signal . I doubt this is my problem (because my speedo seems to have no issue at all - so I think the VSS signal to the ECM is good). Even though ECM self check is good - this seems to be the most probable cause. I'm afraid that getting an ECM is going to be tough.....

[c4zr1]

I tried to find a used ECM for over a year. I finally sent my ECM to Tom Henry Chevrolet to get rebuilt. Good folks to work with and good turnaround time.

[gbmidyear66]

I tried to find a used ECM for over a year. I finally sent my ECM to Tom Henry Chevrolet to get rebuilt. Good folks to work with and good turnaround time.

Do you recall the charge and turn time? I assume they send it out to someone - any idea who?

I have had two recommendations for the same ECM rebuilder - price seems reasonable (but I won't have a driveable car in the meantime).

Thanks

[c4zr1]

This was their response to me.
The ECM that you need is GM part number 88999186 and is list price $426.74 your price would be $266.71. $27.66 in freight .GM has no stock at any warehouse and there is no ETA. We ran the part number on a national locator with no results found.
GM has listed this item as a "Return for Remanufacture" part meaning that we would send GM your old ECM and they would remanufacture it. The time frame for this type of service is listed as 30-45 days from the time that GM receives the module. The above prices are plus any freight charges. We can not estimate shipping charges at this time because we don't know the destination zipcode for the GM reman facility.
We checked the aftermarket suppliers and found that White Racing Products of Tampa, FL. shows one in stock. Their contact information is www.whiteracingproducts.com (http://www.whiteracingproducts.com/) 813-264-6368.
We hope this helps.
Thanks
Tom Henry Parts

[gbmidyear66]

Finally solved. Installed a replacement ECM today - all is good (guess I have a spare VSS sensor now too....). Very strange symptoms from my original.

Got the replacement unit from Whiteracing - could have had my original rebuilt a little cheaper - but would have had maybe 3 weeks of no car going that route.