I keep getting the check engine soon warning on my 94 Sonoma, 4x4, 4.3, 5sp.
It only comes on after about 30 to 40 minutes of driving. The temp is good,
oil pressure is good, oil level seems fine but it's hard to tell exactly
because it splashed up the stick real bad. When I shut the truck off it
resets immediately and I can go another 30 to 40 minutes before it comes on
again. Anybody heard of this before.
Thank you very much for your replies, this is an awesome newsgroup and I
need more help because
this isn't going very well. I tried to read the codes according to the
Haynes manual and it said I have to short pins "A" and "B" on the ALDL
terminal in order to get the "Service Engine Soon " light to flash to the
proper code sequence starting with code 12; which is the code to say the
diagnostic is working properly. My 1994 4.3L is a TBI manual tranmission so
I think I am reading the manual correctly in that I have an OBD 1 model.
When I do the diagnostic the code twelve should flash three times on the SES
but it comes on steady as if I haven't shorted the pins; which leads me to
believe that the PCM is not functioning properly and should be replaced. I
checked pins "A" and "B" and I do have the 5V reference voltage. The manual
doesn't tell me what to do if code 12 does not appear.
94 is an oddball year, 93 was the last ODB-I and 95 was the first real
ODB-II, 94 was sort of a transition year and is somewhere in between, some
call it OBD 1.5. You will need something to read the codes there, the
short A&B won't work.
I've tried every combination possible to read the codes, including a reader
but no luck. I did put a vacuum pump on and the EGR valve is shot. That
should resolve my SES light coming on but I still can't read any codes. I
guess the next step would be to change the PCM. I hate to do that since all
the other functions appear to be working but it's useless if you can't read
the codes. Anybody have any last resort theories before I change it?
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