SES Light, But No Trouble Codes?

[gbmidyear66]

My SES light is comming on intemittently, with increasing regularity. I tried to check it last night in my garage with my AutoXray 60000 scanner - but wouldn't come on sitting at idle.

I drove it today with my scanner attached - wanting to catch the code that is triggering it.

The SES came on about 3 times for 20 seconds or so each time, but there are no trouble codes showing on the scanner? Any way to catch the source of these intermittent SES?

Possibly related.... I am having some idle issues, idle will hang high while driving and/or after coming to a stop (about 2,500, then will eventually come back down), can usually get it to come down to idle (driving or stopped) by blipping the throttle a few times. Checked that my PROM is seated, all my hoses (including MAP) are properly connected, secondary vacumm pump does not cycle, throttle plates are clean and don't seem to be sticking....

Any thoughts appreciated.

[Kevin]

could be 02 sensors

[GOLDCYLON]

Clean your IAC valve located on the side of the airhorn.

[gbmidyear66]

- Cleaned the IAC less than 3,000 miles ago - don't think that is it.

- TPS is reading correct voltage at idle, and ramps up smoothly with RPM

- On the O2 sensors... the voltage jumps around so much on the scanner, but Right and Left seem to be operating in same range and behaving similarly, I'll try to check them a little closer (crosscounts, etc).

[GOLDCYLON]

Trust me its a no cost look. And a dirty one will cause these idle issues. And a lot can happen in less than 3000 miles

[GOLDCYLON]

Are you talking about the Idle Air Controller (IAC) valve on the passenger side of the Throttle Body?

The Manifold Air Temperature sensor (MAT) is located on the passenger side of the Airhorn (Throttle Body Extension).


IAC it is further back on the TB behind the Airhorn :handshak:

[tomtom72]

Well, your O2 sensors seem to be okay by your description of the voltage behavior. They are supposed to change voltage so quickly as to make you dizzy.

Have you tried getting into the CCM? Sometimes if the DTC will not set the CCM picks it up & stores it as an "H" code, History code. I can't recall which pins on the ALDL to short.......I have Gordon's jumper kit, yea I cheat!:o

Let me ask, steady state cruise? Or hard acceleration? or moderate acceleration? Or steady high speeds like over 80 mph? Or it just has a mind of it's own?

Also, which base management program are you using? AUAH or AYBK? The 90's had a TSB on the AUAH program for the idle & coast down symptoms you're describing and the AYBK prom was issued to correct those symptoms, albeit in 1992!

:cheers:
Tom

[gbmidyear66]

Tom - that is very intersting. I tossed out the paper clip when I bought my AutoXray (but have a good supply in my desk...)

Do you happen to know the procedure to retrieve the "H" codes from the CCM?

I am getting the intrermittent SES under normal city/highway (mixed) driving, usually starts to appear after about 10 minutes of operation, it seems to be getting more frequent though - happened 3 times on my 20 minute drive in to the office today.

I've been runniung a "custom" prom on a Moates adapter for a year now. I have the original AUAH (with the stupid CAGS and the stupid high idle until dead stop) - I may put that back in just to see if it makes a diff - but I already pulled the adpater to make sure everything was seated well.

[GOLDCYLON]

Have you tried getting into the CCM? Sometimes if the DTC will not set the CCM picks it up & stores it as an "H" code, History code. I can't recall which pins on the ALDL to short.......I have Gordon's jumper kit, yea I cheat!:o :cheers:
Tom


Tom is right a CCM code could be set

[tomtom72]

You Da Man Cliff!:worship:

Terminal "A" is ground and terminal "G" is the line to the CCM. As you view the ALDL, A is top right and G is lower row left. Short those two and the speedo will dissolve into a data stream for the CCM, trouble is that I don't remember the rest as there are 4 modules of display......that stuff is in the Kit from Gordon so I never bothered to memorize it as it's always in my car.:o

Oh, the CSGS can be unplugged at the trans and left tapped up to keep dirt & such out of the connectors. The Prom don't care that it is unplugged, no DTC is set.

Okay, now this is an admission of stupidity on my part. I'm lost when you guys talk about MOATS stuff. Flightless birds & emulators & all that good chit I should learn.... but anyway I'll lay this on you because I have a piggy back thing plugged into my OE AYBK PROM and I lost the foam block on the door of the ECM. This is causing the PROM to loosen as I drive, and unless it gets real loose it doesn't even light the SES light, even flicker it. My issue is that the PROM cover had to be removed to plug in the piggy back thing, and now the hold down levers don't have anything to grab, they used to grab the stock prom cover ( that blue thing that the foam block used to rest on when the door is locked ) so it vibrates loose and is playing heck with the ECM.....I think it goes into retarded mode. Anyway, a loose prom is supposed to set a DTC 51 or a DTC41: 51= wrong or loose memcal; 41 = cylinder select error, which could also be a loose memcal.

Okay that's the sum of my knowledge on engine management programs and their workings!:o

:cheers:
Tom

[XfireZ51]

Tom,

I use a Moates adapter for my Ostrich and the stock prom is not what is plugged into the ECM socket. The adapter plugs in while the stock prom hangs sideways into the body of the ECM. The prom retainers clip onto the adapter in my install and hold it there. The problem area for the adapter is the prom/adapter connection. Because it hangs sideways, the prom vibrates and can cause it to loosen from the Adapter. You can smear a bit of clear silicone across that interface to help out with the vibration.
The other alternative is to erase the stock prom and burn the new cal onto it avoiding the use of the adapter all together. I run the car off the Ostrich pretty much all the time, but on a long trip I will have a prom with a good enough cal on it in case something goes wrong.

As for the intermittent SES light, you're not setting a hard code. It would help if you datalogged your drive and earmarked points where the light came on.
I have had this happen w the O2 sensor lean/rich codes. I was getting into secondaries and fuel pump was not providing enough fuel so I had a momentary lean condition. Replaced pump and strainer(s), problem
solved.

[gbmidyear66]

Tom, GC - thanks for the suggestions.

- I have done a bit more troubleshooting, and the evidence as I interpret it is pointing to sticking throttle plates.

- Pulled the IAC, it was clean (I could also see it was functioning using the scanner)
- Pulled the MAP sensor to check for oil in the vacuum line, it was clean
- Drove around reading the data stream on my AutoXray (they've banned hand held cell phones here - but I have not heard any mention of scanners....) - when I have the high idle, I can see that the TPS is back down to normal value for idle (0.55V) but I can also see that when I have the high idle that the MAP sensor voltage was really low, about 0.6V, it is normally about 1.25 at idle - I believe this is telling me I have low vacuum - or excess air getting in causing the high idle? Does that make sense?

- I also pulled the codes from the ECM using the paper clip (actually pins A and B on the ALDL on a 90), it gives a code 24 (Vehicle Speed Sensor) - possible cause is listed as TPS (maybe it triggers this when TPS is at idle and my RPM is high?)

- I'm going to put my stock PROM in - just to rule that out, but I believe my problem is most likely the throttle plates sticking - does that make sense?

[XfireZ51]

Try cleaning the throttle plates and the throttle body openings. Then see if you get same TPS reading or if it now needs adjusting.
BTW, the scanner will show you what IAC STEPS are COMMANDED by the ECM,
not the actual steps. Make sure the IAC orifice is also clean.

[LGAFF]

Feel your pain, going through the same issue with the Callaway TT...posts on the Corvette Forum.


-replaced IAC
-replaced coil
-replaced TPS
-replaced MAF Relays
-replaced MAF
-Tested injectors: resist/pulse both ok
-no blown fuses

Car runs only with MAF disconnected; sets a code 33..per the FSM means ECM is good and MAF bad...so replacing the MAF sensor should have solved it one would think.

[LGAFF]

Dom,

How about a newsletter article on how to use diagnostic programs...maybe the essentials needed for a startup kit?

[Kevin]

Feel your pain, going through the same issue with the Callaway TT...posts on the Corvette Forum.


-replaced IAC
-replaced coil
-replaced TPS
-replaced MAF Relays
-replaced MAF
-Tested injectors: resist/pulse both ok
-no blown fuses

Car runs only with MAF disconnected; sets a code 33..per the FSM means ECM is good and MAF bad...so replacing the MAF sensor should have solved it one would think.

did you try posting on the callaway forum? CF seems to be a collection of morons for the most part. also you could give gordons website a look.

[XfireZ51]

Dom,

How about a newsletter article on how to use diagnostic programs...maybe the essentials needed for a startup kit?

Lee,

What's the car doing?
I'll be glad to do that. I'm using EASE personal which I don't believe is available any longer. Another alternative is ScannerPro but the .adx (aldl) files need to be built. I think =Jeff= has it for the 90 Z.