SES light, no codes
Thread Starter
Safety Car
Joined: May 2007
Posts: 3,651
Likes: 10
From: Apple Valley MN
SES light, no codes
Last week on the way home from the office, my Service Engine Soon light came on on - guages all read normal, and it was running fine. I pulled the codes when I got home, and there were none. I disconnected the battery for a few minutes, and when I restarted it, the SES light was off. I drove it several days with no trouble. This morning, the light came on again on my way to the office - I won't be able to pull the codes until I get home tonight. Assuming no codes, does anyone have a clue what could be causing this?
Background - it's an LT4, and this spring I've put in a new water pump, MSD opti, plugs, wires, coil, SW long tube headers with Random Technologies cats, and kept all the emissions intact (AIR tubes and O2 sensors). I also installed one of those larger MAF housings from MidAmerica.
Background - it's an LT4, and this spring I've put in a new water pump, MSD opti, plugs, wires, coil, SW long tube headers with Random Technologies cats, and kept all the emissions intact (AIR tubes and O2 sensors). I also installed one of those larger MAF housings from MidAmerica.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
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From: Orlando FL
Are you pulling the codes with the on board diagnostics which displays on the speedometer. I only ask this because I know the 96 is OBD2. Is it a possibility that looking at the codes with a external code reader or scanner might show up additional information. I know there are tons of OBD2 codes (unlike OBD1 for 95 and down) and another reader might show them up.
I realize this is some speculation on my part since I have a 94, but just a thought. My other thought is that the PCM might be getting flaky. If something is momentary sensed causing a glitch and the SES is turned on, you would think there would be a code set with a normally working PCM.
I realize this is some speculation on my part since I have a 94, but just a thought. My other thought is that the PCM might be getting flaky. If something is momentary sensed causing a glitch and the SES is turned on, you would think there would be a code set with a normally working PCM.
Thread Starter
Safety Car
Joined: May 2007
Posts: 3,651
Likes: 10
From: Apple Valley MN
My wife had bought me an OBDII scanner for Christmas, and it didn't work for some reason, so I used the paper clip method. The display on the speedometer cycled through all the modules, and came up with C12 (if I remember correctly), or whatever code it was that indicates that there are no codes.
Le Mans Master
Joined: Sep 2003
Posts: 5,874
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From: Littleton CO
My wife had bought me an OBDII scanner for Christmas, and it didn't work for some reason, so I used the paper clip method. The display on the speedometer cycled through all the modules, and came up with C12 (if I remember correctly), or whatever code it was that indicates that there are no codes.
You'll need to try another reader or scanner. Mine was from Harbor Freight and works well for getting the OBDII codes. For some reason, it does not see the CCM codes, though. Go figure.
Last edited by jrp; Apr 29, 2008 at 10:06 AM.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
I find this an interesting post because I have always wondered if the on board will work the same for a (96) OBD2 system. The SES light relates to the PCM and SYS light to the CCM. Having said that if you look at a site like the corvettedoctor, it leads you to believe that the codes (module 4) for the 96 can be retrieved as earlier years.
http://www.corvettedoctor.com/1994_96_DTC_Codes.html
I have never read a 96 FSM and don’t know what it says about DICs in module 4 (PCM). I believe that C12 indicates there are no codes but only in regard to module 1. Most who talk about codes always assume they are for the PMC (or ECM), but there are a whole set of separate codes for the CCM in module 1 which controls the car excluding brake system. Engine related problems (PCM, module 4) get the most attention are what are most talked about so that what everybody zeroes in on.
I got my OBD2 code reader form harbor freight also. Got it on a great sale and is yellow works great on my OBD2 cars. Comes with a CD which has generic and manufacture specific OBD2 code translations. It will not work on a 94 or 95 vette even though it will physically mate up. Electronically it will not communicate, the protocol is wrong.
http://www.corvettedoctor.com/1994_96_DTC_Codes.html
I have never read a 96 FSM and don’t know what it says about DICs in module 4 (PCM). I believe that C12 indicates there are no codes but only in regard to module 1. Most who talk about codes always assume they are for the PMC (or ECM), but there are a whole set of separate codes for the CCM in module 1 which controls the car excluding brake system. Engine related problems (PCM, module 4) get the most attention are what are most talked about so that what everybody zeroes in on.
I got my OBD2 code reader form harbor freight also. Got it on a great sale and is yellow works great on my OBD2 cars. Comes with a CD which has generic and manufacture specific OBD2 code translations. It will not work on a 94 or 95 vette even though it will physically mate up. Electronically it will not communicate, the protocol is wrong.
Le Mans Master
Joined: Jan 2006
Posts: 5,621
Likes: 206
From: Orlando FL
Drifting
Joined: Jun 2005
Posts: 1,426
Likes: 1
From: brookville pa.
egr
i think what happens is carbon builds up in valve restricts flow when you run car at high rpm, at least that what my problem was. light did not come on everytime i drove it just seems to light up when i ran it hard, when i did away with egr no more light
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Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
I have heard of this but always thought it was the EGR solenoid. The solenoid is monitored and driven by the PCM/ECM. So it can make a call as to if the voltages are right at the times of monitoring. But the EGR is a vacuum driven device and the computer would not know what its doing because it is not monitored. The vacuum only flows thru the solenoid.
Le Mans Master
Joined: Sep 2003
Posts: 5,874
Likes: 0
From: Littleton CO
I find this an interesting post because I have always wondered if the on board will work the same for a (96) OBD2 system. The SES light relates to the PCM and SYS light to the CCM. Having said that if you look at a site like the corvettedoctor, it leads you to believe that the codes (module 4) for the 96 can be retrieved as earlier years.
http://www.corvettedoctor.com/1994_96_DTC_Codes.html
http://www.corvettedoctor.com/1994_96_DTC_Codes.html
Details & diagnostics for each individual OBDII code are easily looked up, but I have yet to find mention of how they are really retrieved in the first place.
Thread Starter
Safety Car
Joined: May 2007
Posts: 3,651
Likes: 10
From: Apple Valley MN
I just got home, and am waiting for FedEx to come pick up a package, so I poked around a bit. I found that the connector to the MAF wasn't snapped in tightly. So I disconnected the battery to reset the light and will see if that does the trick. If not, I'll swing by AutoZone next time it happens. I need to figure out what's wrong with the gizmo my wife got me - it's called a V-Checker:
http://www.vchecker.com/product/OBDBASIC.htm
http://www.vchecker.com/product/OBDBASIC.htm