Check engine light on?

My wife to take the truck to get a ca. Smog test. She noticed the service engine light did not come on when she first turned the key on. Before starting. Any ideas where start to trouble shhot this one fuses all look good. Maybe a bulb? Or is a sensor to test. Ca. No light at start up is automatic fail. Any ideas would be great.

Thanks. Im looking it up now

Replaceing thermostat on 97 ford ranger 4.0
engine light on.

I had a diaignostic check it showed the thermostat was bad. I need to know how to replace it.

Thanks
Leonard Smith

I have been driving more than normal and my check engine light came on today. The engine is okay on all fluid levels and is not overheating. Is this most likely an O2 sensor or could it be anything? Is it safe to drive or do I have to get it checked right away?

I just bought this truck for work but I am having a problem figuring out this check engine light

The engine runs good, slightly rough idle and I don't think it is getting the best mileage. I also think it is quite low on power. I cleaned the MAF thinking this may be the cause but did not seem to change anything. I cleaned it with an electrical cleaner that does not leave any residue.

Also, once I reset the MIL code, it seems to reappear after about 50 miles but it will be quicker if I'm using my a/c, which cycles too much (probably low on refrigerant)

I'm not one to throw a lot of money at a vehicle with this many miles so hopefully you can help me. I don't like to replace parts until I'm sure they are bad.

The code I'm pulling is P0712 - System too rich (Bank 1)

Here is the info I got from the scanner:

I/M monitors:

Misfire Mon: OK
Fuel Sys Mon: OK
Comp Component: OK
Catalyst Mon: INC
HTD Catalyst: N/A
Evap System Mon: N/A
Sec Air System: N/A
A/C Refrig Mon: OK
Oxygen Sens Mon: INC
Oxygen Sens HTR: INC
EGR System Mon: OK

Freeze Dat

Engine RPM: 1576
Load Value: 78.0%
Coolant Temp: 188f

Short Term Fuel Trim 1: -5.1%
Long Term Fuel Trim 1: -16.1%
Short Term Fuel Trim 2: -5.1%
Long Term Fuel Trim 2: -16.1%
Short Term Fuel Trim 3: 53.9%
Long Term Fuel Trim 3: 47.6%
Short Term Fuel Trim 4: 59.3%

Speed: 32mph
Fuel System 1: CLSD
Fuel System 2: N/A

Any help will be greatly appreciated!

I removed the vacuum hose to see if there was any fuel in it but it was dry.

Also, what do you think would be the most likely cause? I looked at the O2 sensors and they actually look pretty new.

Thanks for your help!

My 95 ranger starts and goes dead starts and goes dead does this for a while and finally cranks trucks runs great thought it was a fuel problem replaced filter and checked fuel pressure everything is fine seems like a sensor problem or computer but my check engine light is not on.