nvlav8tor

Last night I pulled the codes off my 94 coupe, because the sys is blinking at me. Here's what I got: C34, H33, and H34. Does anyone know the difference between an H and a C code. I know one of them has to do with the MAP sensor, but that's it. I would appreciate your input. :flag

rick lambert

I can't answer your question, :( but you might want to go to http://www.c4vettes.com/ecm.htm-I have no idea what the letters account for :rolleyes: I suspect the codes themselves are what you should focus on.

GOOD LUCK :seeya

nvlav8tor

Thanks Rick, but that site is currently down for construction. Or, I might be using it wrong. Do you know what link I should click on? :flag

Tony.96LT4

Don't know if a 94 is the same as a 96 but "sys" codes 33 and 34 deal with the data clock. 33 is Data clock circuit shorted to B+ or CCM internal open. 34 is Data clock circuit open or shorted to ground. "H" I think stands for history readout and "C" stands for current readout. Hope this helps.

nvlav8tor

Thanks for the input. I've tried installing resistors and a new battery, I just can't seem to beat this thing. :flag

ittlfly

Sending you an email with attachment that may help. Good luck.

SunCr

C means current; H is history so it's no longer present. You can clear them and see what comes back - should be the 33, but it's curious that you had both. These are MAP codes. How's performance/idle? The 34 means the idle voltage was high when it should have been low. It can be a bad ground but with both codes, you might suspect the reference wire or PCM (which depending on your mileage, might just be covered under the Fed Emissions warranty). Gray is the 5 volt reference. Green is the return. Black is ground. MAP range is 1 to about 4.8 volts. At idle, it should be about 1 to 1.5; WOT 4.5 to 4.8. The 33 means the voltage remained low with engine speed above 700 rpm, so another suspect would be the green wire, the connector or the MAP itself. As to the wiring, no-one spliced in a new harness did they? I only mention this because I experienced this once - some idiot (who will remain nameless of course) crimped in a new harness after breaking the MAP connector. the crimp loosened creating an intermittent stall that took two dealers plus the original DIY to diagnose. You're lucky to have codes - check the wiring carefully.

SunCr

Just remembered - check the vacuum supply to the MAP too!

nvlav8tor

Thank you so much! I'll give it a shot. :flag