Check Engine Light, No Codes

OK, this is a puzzler.

The CEL is on in my 1995 850 (non-turbo). It comes on about 5 seconds
after the car is started and remains on. There are NO codes. The only
blink code is the "I'm OK and there are no other codes" code. My OBD
scanner shows no codes or pending codes. Pretty sure it's not the gas
cap, FWIW.

I've seen lots of odd automotive things, but never a CEL with no codes!

Any ideas?

JRE

 

The CEL is just a powered bulb grounded through the PCM. While there
are DTC's which will not show up on a generic code reader or in the
blink sequence, they are pretty much limited to internal PCM logic
issues. Your Volvo dealer can extract them if you're curious. More
likely you have a ground fault somewhere in the dash circuits.

 

This turned out to be a transmission code. No clue why my scanner and
the blink codes wouldn't show it, since it's a generic OBDII code.
P0715, transmission speed sensor. The code's reset for now and I'll
plan to do the resistance check this weekend.

 

The reason is that the OBD2 reader just reads the engine control module
so as in your case the DTC was set in the transmission control module as
the other poster stated the dealer is able to read out all systems in
the car with the Volvo System Tester (VST) this is made to read all systems

 

I have a similar issue on my 1995 850, the CEL light is stuck on and
my code reader doesn't show any code consistently. Occasionally I get
a P0755 to come out (something about a transmission selenoid) but then
it goes away.

Let me know what you find.

Mark