Hi Guys

Since I bought this vette ('93 LT1) I have had a code 28 that turns on the SES light.
I disconnected the battery ground to clear the codes (had a couple of other codes that haven't come back yet) and took the car out today to get some gas, a round trip of about 18 miles. The car ran ok, no SES light until I got almost home (within 1/2 mile).
When the SES came on, it killed the motor, then it would not restart until I flashed the trouble codes (via paperclip in the ALDL).

I haven't done any troubleshooting yet, the previous owner said the code 28 had been there for a while and suspected an iffy a/c compressor wire/connector, I had the a/c turned off today during the trip.

Would this wire/connector cause the engine to die?, or am I looking at a potential ECM problem?. Is there an 'easy' way to pinpoint the true cause without a scanner?.

Any help or advice would be appreciated.
Thanks
Sara Lou

 

It would be a good idea to try a "real" scanner while driving the car. A code 28 by itself will not turn on the SES light.

 

What would be considered a "real scanner" for these OBD1 cars?

 

'28' is all I am getting when I pull codes via the paperclip in ALDL. I do have datamaster, but it is intermittent at best, and i'm weary at driving this thing while its dying randomly.

When I drove it today, I travelled about 9 miles to the gas station, turned the car off and put gas in. It fired right up when I left the gas store, and I drove back home without problem until I got within 1/2 mile of home (8 1/2 mile return trip), at which point SES light comes on and it died and would not start.

I pulled codes and got a '28', it started after removing paperclip, got about 1/4 mile and it died again. Same senario, no start till I pull codes, same code '28'.

Sara Lou

 

Anyone?.

Sara Lou

 

Basic codes below. 28 does not look like it would shut the car down but I'm not sure about that. Maybe someone else can help.

DTC - 12 No distributor reference pulse (diagnostic test active)
DTC - 13 Oxygen sensor circuit open or no activity
DTC - 13 Left bank O2 sensor circuit open or no activity
DTC - 14 Engine coolant temp sensor error (high temp indicated)
DTC - 15 Engine coolant temp sensor error (low temp indicated)
DTC - 16 System voltage too low
DTC - 17 Camshaft position sensor error
DTC - 21 Throttle Position sensor error (signal high)
DTC - 22 Throttle position sensor error (signal low)
DTC - 23 Intake air temp sensor error (low temp indicated)
DTC - 24 Vehicle speed sensor error (open circuit or no activity)
DTC - 25 Intake air temp sensor error (high temp indicated)
DTC - 26 Quad Driver Module (QDM A) error
DTC - 28 Auto transmission range pressure switch error
DTC - 31 Wastegate solenoid circuit error
DTC - 31 Gear Position Switch (PRNDL) error
DTC - 32 EGR system failure
DTC - 33 MAP sensor circuit error (signal high indicating low vacuum)
DTC - 34 MAP sensor circuit error (signal low indicating high vacuum)
DTC - 35 IAC problem or idle error
DTC - 36 MAF sensor error
DTC - 36 24x Crankshaft position sensor circuit error
DTC - 36 4T60-E Shifting Error
DTC - 37 TCC brake switch circuit error
DTC - 38 TCC brake switch circuit error
DTC - 39 Clutch switch circuit error
DTC - 39 TCC error
DTC - 41 Ignition control error
DTC - 41 MEM-CAL error
DTC - 41 C³I Cam Sensor Signal error
DTC - 42 Ignition bypass circuit error
DTC - 43 Knock sensor error
DTC - 44 Oxygen sensor error (lean condition indicated)
DTC - 44 Left bank O2 sensor error (lean condition indicated)
DTC - 45 Oxygen sensor error (rich condition indicated)
DTC - 45 Left bank O2 sensor error (rich condition indicated)
DTC - 46 Pass-Key II (VATS) system error - circuit out of freq range
DTC - 47 UART (serial data) circuit error
DTC - 51 PROM error
DTC - 51 Incorrect MEM-CAL
DTC - 52 Fuel cal-pak incorrect or missing
DTC - 53 System voltage too high
DTC - 53 Digital EGR Valve solenoid 1 error
DTC - 54 Fuel pump circuit low voltage
DTC - 54 Digital EGR Valve solenoid 2 error
DTC - 55 ECM error
DTC - 55 Digital EGR Valve solenoid 3 error
DTC - 56 Quad Driver Module (QDM B) error
DTC - 57 Boost Control error
DTC - 58 Trans fluid temp sensor circuit error (low voltage)
DTC - 58 VATS system error
DTC - 59 Trans fluid temp sensor circuit error (high voltage)
DTC - 61 A/C system performance
DTC - 63 Right bank O2 sensor circuit error
DTC - 63 MAP sensor circuit signal voltage high (low vacuum indicated)
DTC - 64 Right bank O2 sensor lean exhaust indicated
DTC - 64 MAP sensor circuit signal voltage low (high vacuum indicated)
DTC - 65 Right bank O2 sensor rich exhaust indicated
DTC - 66 A/C pressure sensor circuit error (low pressure indicated)
DTC - 67 A/C pressure sensor circuit error
DTC - 68 A/C clutch relay circuit error (shorted to ground)
DTC - 69 A/C clutch relay circuit error (open circuit indicated)
DTC - 69 A/C high pressure switch error
DTC - 70 A/C pressure sensor circuit error (high pressure indicated)
DTC - 71 A/C evaporator temp sensor circuit error (low temp indicated)
DTC - 72 VSS signal circuit error
DTC - 73 A/C evaporator temp sensor circuit error (high temp indicated)
DTC - 75 Digital EGR solenoid #1 circuit error
DTC - 76 Digital EGR solenoid #2 circuit error
DTC - 77 Digital EGR solenoid #3 circuit error
DTC - 79 Transmission fluid overtemp
DTC - 80 Transmission component slipping
DTC - 82 3x Crankshaft position sensor circuit error
DTC - 85 PROM error
DTC - 86 A/D error
DTC - 87 EEPROM error (flash memory error)
DTC - 90 TCC error
DTC - 93 Transmission pressure control solenoid circuit error
DTC - 96 Transmission system voltage low
DTC - 98 Invalid PCM program
DTC - 99 Invalid PCM program

 

What were the other codes that cleared?

That 28 is coincidence... you have fuel issues...filter or pump. Pressure test fuel system. Go from there. Next would be ignition.

 

The other code was a O2 sensor, but that hasn't come back.
After it dies (soon as SES light comes on), it will turn over but won't start. I then have to 'flash' the codes (all I get is '28') before it will start again.

The previous owner assured me he changed out the fuel pump just before I bought it, but didn't do the filter. It runs ok (not perfect, but reasonable, like it needs a tune-up), right up until the SES light, then BAM, it dies.

Looking up code '28' says it's "Quad Driver Module Number 3". Which I believe is A/C and fan relay related, but I also read somewhere it may have something to do with the VATS system inside the ecm too, which, the way the car behaves is something I feel may have a lot to do with the problem.

Sara Lou

 

Code 28 on a 92/93 LT1 Corvette is the "Quad Driver Module Number 3" DTC which is related to the AC system (fan(s) and AC clutch). Code 28 will not turn on the SES light by itself as it is not considered critical.

Anytime the engine stops running (stalls) in the key on position the SES light will come on. It does not necessarily mean a related code has been set.

Code 28 could conceivably be related to a stall condition but it is more likely that your problem lies in the fuel or ignition system. A FSM (Factory Service Manual) will help you get to the bottom of this. A fuel pressure gauge and some way to check for spark will allow you to start isolating the problem.

 

THANK YOU!! . That explains a lot to me. Knowing that the SES light is a consequence of the stalling and not the cause, makes understanding the problem so much simpler.
When it is explained to me like that, I can now comprehend what everyone was telling me that the '28' was not my problem. I will now approach this diagnosis without the mindset of the 'haunting 28'.

I will start with the fuel system, mainly because I hear the pump prime whenever I turn the key to 'on', whether or not I attempt to start the car, the pump will prime everytime I turn the key, which tells me its not holding pressure.

Sara Lou

 

The pump will prime for 2-3 seconds every time you turn the ignition on. You still need to check that pressurized fuel is getting to the engine with the guage.

 

Really I didn't know that. I was basing my assumption on my firebird ('94), once it has primed, it holds pressure and doesn't prime again when the key is turned off and back on.

I'm assuming the fuel pressure valve is the thing on the fuel rail (passenger side) that is upside down and looks really hard to get too!!.

Sara Lou

 

It looks hard to get too, but you can remove the cap from the schrader valve and hook a fuel pressure gage on there without too much trouble - small fingers help.
Please buy a factory service manual TODAY. It will take a while for it to arrive and we can help you out until then. The $100 you spend on it will save you thousands of dollars later.

You are looking for 40 psi when the pump primes the rails. Once its primed leave it connected for an hour to make sure it stays around the same psi. If it leaks down then you have leaky injectors or bad fuel pressure regulator.

Good luck - and Welcome!

 

The quad driver chip will set a fault condition if it sees a short or open on whatever it is controlling.

I looked at the schematic for this car and see 3 quad drivers. It's not clear to me which one is which, but based on the post by bjm206 it looks like #3 is U18, which controls the SES light, the cooling fan, and pin E9 and pin F7. I don't know what E9 and F7 connect to on your car. The FSM would tell you. Maybe somebody more knowledgable can help out with this.

For reference, the schematic is here:

http://www.exatorq.com/ludis_obd1/1227749schematic.html

This is a mirror site of Ludis Langens' old site, which disappeared into the mists of the Internet past around 2004 or so. Too bad. He made a HUGE contribution to the knowledge base on these old cars.

 

Thanks for the info guys, and thanks for the welcome jaa1992.

Thats pretty mind-blowing stuff Clliff!!. Looking at the link you posted everything i'm having problems with connect to the same thing (U2). Electronics are waaaay over my head.

Sara Lou

 

I use to look at that (Ludis Langens) site also but not for a while now. But just checked it out and it is still up and running.

I think there was another site on ECM repair but can't find that anymore.

 

If your car is showing signs of over heating and your ESC light continues to come on I would change the EGR valve on the top and back of the engine. I had the same problem and after changing the EGR valve I had no more lights, an engine that ran cooler, and at lest another 25HP working for me. The EGR valve must be replaced every 15,000 miles. Auto Zone for $52 with a life time gurantee. Try it and you will like it! The EGR valve redirects hot exhaust gases back into the intake manifold. When it goes bad, like mine did, it allows to much exhaust into the engine resulting in over heating. I was getting DTC48, DTC28, DTC43. The hot gagses where causing some engine knocks that caused the DTC43 to activate. You can use the codes but you should consider purchasing the mantenance manuals that help you to anylize the problem.