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How do I reset the SES light?

GuyzVette

Well-known member
Joined
Dec 19, 2005
Messages
86
Location
Wichita, KS
Corvette
Polo Green 1994 LT-1
A little while back, I had a service done to clean the plenum. They had to disconnect the air intake. Doing so tripped the SES light. They unfortunately only had a ODB II computer and could not reset for me. I've tried disconnecting the battery for a while, and someone said 50 starts, but I'm way past that.

Do I have a problem now, or is there a way to manually clear that code? Pretty explicit directions would be very nice, as I have never messed with the codes on this car.

Thanks!
 
Joined
Jul 28, 2004
Messages
799
Location
Phoenix, AZ
Corvette
Blk/Blk '96 LT4 Coupe
You can get a OBD1 code reader off eBay for somewhere around $20. That will read the code/s for you and allow you to clear them - SES light off. Another option; go to any Autozone and have them read the code/s for free...they will do it and clear them for you at the same time. My guess is you may have some sort of problem cuz the SES should have gone off by now. Once you have the code/s read, post them and maybe we can help you troubleshoot.

Jeff :beer
 

GuyzVette

Well-known member
Joined
Dec 19, 2005
Messages
86
Location
Wichita, KS
Corvette
Polo Green 1994 LT-1
Okay, finally took the car by Autozone, and they couldn't read the codes. 1994 and 1995 have the ODB I module, and the ODB II connector. Go figure. So I finally find out through searching forums how to ground out the new connector (pins 4 and 12, btw), and I get one code only. H48. Searching says something about the MAF sensor circuit. I've wiggled the wiring (recommended) to see if anything is loose. Also checked the wires for any problems. Doesn't seem to be anything.

Disconnected battery to reset SES, and it trips again, right away.

Anyone have a clue as to my next step on diagnosing the problem?
 
Joined
Jul 28, 2004
Messages
799
Location
Phoenix, AZ
Corvette
Blk/Blk '96 LT4 Coupe
This is where the FSM (factory service manual) would come in handy - I'm assuming that you don't have one for your '94. The FSM has the steps you need to follow to troubleshoot the code/s. Unfortunately, I'm at work and my FSM for my '96 is at home. I'll keep an eye on this thread and if noone is able to help by this evening, I'll take a look at my FSM and see what I can come up w/ regarding that code. I'm not sure if my FSM will cross-reference to the OBD1 codes (since mine's OBD2) but we'll see...

From what I've learned w/ my car, just because a code points to a specific part/system doesn't necessarily mean that that is the problem. It means that the problem (whatever it may be) is causing that part/system to throw a code...so you definitely don't want to just start throwing parts at it.

The FSM is the key here and definitely an item you need to have.

Jeff
 

GuyzVette

Well-known member
Joined
Dec 19, 2005
Messages
86
Location
Wichita, KS
Corvette
Polo Green 1994 LT-1
Haven't been here in a while, and I've been busy. I was searching this thread for something else, and saw my thread here, and I had left it unresolved. I apologize. I found someone with a car like mine, that had the manual like mine. The manual was a little difficult to try to pinpoint the problem, but what I WAS able to do, was to look at his car, and then look at mine. Problem was the MAF sensor connector on the bottom of the air intake was not connected. And the wire had fallen down where I couldn't see it. It wasn't until I saw the other car, with the connector, that I could tell something was missing. I could also find out where the wire came from and track it down in mine.

So, thanks for all your help!
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
Most 94s and 95s, except ZR-1s, were part of GM's "early rollout" of OBD-II diagnostics.

The ECMs in those car have full OBD-I systems along with "partial OBD-II capibillity." These systems' OBD-I works like other 81-93 systems. The partial-OBD-II was there only for the program GM was running at the time which collected data about the field performance of their OBD-II system. Any OBD-II codes set would not turn on the SES light but would store a code. Anytime one of these cars came into a dealer, the dealer read the OBD-II side of the system and, if codes were set, sent a report to GM. At the time, the only equipment which supported this partial OBD-II capability was the dealer scan tester, the Vetronix TECH 1A fitted with an OBD-II auxiliary software cartridge and a 12-to-16 pin adapter.

As for OBD-II hardware, all 94-95s had the 16-pin DLC and had some of the sensors, actuators and wiring harness which would be come standard in 1996.

The pin 4-12 connection is for CCM diagnostics and the H48 code, which you saw on the IP display, is a history code. 48 sets whenever the ECM detects engine reference pulses but no signal from the MAF. As long as the SES is not on and you don't see "C48", then it
s a fault that may have been a one-time deal or is an intermittant that's happened in the past, but is not occuring now. I'd clear codes and road test. If you don't see the check engine light, again, I'd not worry. If the code sets again, then I'd troubleshoot according to the DTC48 information in the Factory Service Manual.

You can clear codes on a 94-95 by either 1) disconnecting power to the ECM for at least 30 seconds, 2) disconnecting the battery for 30 sec., 3) using the clear codes feature of a scan tester or 4) using the CCM diagnostics (pin 4 to 12) code clearing instructions listed in Section 8D of the FSM.
 

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