I have a 96 ranger 3.0 that failed CA smog. It passed visual and emissions test. But failed the MIL/check engine light test. The odd thing is that there were 0 codes and the light is off. It failed cause of the non-continuous monitor test. Its not reading the catalyst, O2 sensor, O2 sensor heater and the EGR system. Not sure what to do next. I was wondering if anyone has run into this before. Or should replace the O2 sensors and retest it?

 

The O2 sensors should be replaced on 80,000 mile intervals as schedule preventative maintenance. If you haven't replaced them, you should consider doing so. There must be some codes. Find someone with a more powerful scan tool, some of the cheaper tools will only read generic codes.

 

The PCM remembers it's settings the same as your radio does.

Take a quick look at the 96 Ranger"engine controls wiring diagram" and check any fuses that are "hot at all times" and are wired to the PCM.

 

Khan: the smog shop said there were 0 codes.
XLT: I will do that and let you know if I find something.

 

Well I found a 20a maxi fuse that was blown. It powers the PCM memory. Hopefully that was the problem. Going to go and retest.

 

Yep that was your problem. Good job with the fix.

Now you will probably need to drive it for awhile while it learns it's new settings.

 

Thanks for the help. Im going to drive it over the weekend and plug it ino my scan tool and see if anything has changed.

 

Truck passed smog. Thanks for the help Khan and XLT

 

Well it's been a good week for the both of us, my 87 Ranger also passed calif smog with no problems last thursday.

Thanks for the update, i'm glad to hear you got it squared away.

 

ok newbie here to the little Rangers. We just bought my son a 93 XLT ranger 4x4. The MIL does not light up when you turn the ignition on, which means either the bulb is burned out, missing or something else. I have not had a chance to check it yet, and the smog station told my son that needs to be fixed before he can test it. So how does the gauge cluster come out in a 93 so you can get to the dash bulbs??

 

O2 sensors don't need to be replaced regularly, it's a waste of money. My 2002 has 4 of them that would cost a fortune. I just smogged my truck with 85k on it and flew through smog with 0.00-0.01 emissions. If you keep you vehicle maintained and tuned-up it wont burn up the 02 sensors.

 

93 Ranger XLT 4.0L update:
well I pulled the dash and the cluster, replaced the MIL bulb, sure enough it was burned out. Fired up the engine and it lit up within 5 seconds. I don't know how many codes I have, and we tried to figure them out by watching the MIL flash during the test mode. I could not make any sense out of it, so I am waiting for my new digital scan tool to show up and reads out each code number without having to count the flashes, then I can start the repair process. The truck seems to run ok, just a little rough and the idle seems to change slightly whenever it wants, so I am thinking IAC might be on the way out. Just gonna wait till I get the right codes from it and go from there...

 

Thats an opinion, what do the automakers and sensor manufacturers say about the sensors? You don't need to replace all 4 of them. I'll tell you what does cost a fortune. Catalytic converters cost a fortune. Keeping the vehicle tuned is not the answer, because no fuel is perfect, it is contaminants in the fuel that causes the sensors to fail. When the sensors go, the vehicle invariably runs rich.

O2 sensors are maintenance items. I just replaced the front 2 on my Taurus, installed for $208. The newer air fuel ratio sensors are more costly. If you wait for the computer to set failure codes on the sensors, its too late, they have already caused damage to the sensors and EGR, and have already left carbon deposits in the engine. These problems are not always immediately apart, though most of the time, either the converter will fail or you will get an EGR code long before the computer ever detects that a faulty O2 sensor was the original source of the problem.

A new dealer converter for your truck can cost over $1200, thats a heck of a lot more than the price of 2 O2 sensors. Even aftermarket converters can run as much as $600. And they will fail repeatedly unless the source of the problem is corrected, and most of the time, thats a faulty O2 sensor.

A quick way to check the function of the sensor (you have to make an assumption here, that the MAF is good and that several other sensors are working) is to take a scan tool, which not everyone has, and check the LTFT on both banks. If either bank is more than +3%, then the sensor has likely begun to deteriorate, and that is more than rich enough to cause carbon deposits to start forming, which in turn starts damaging other systems. If your LTFT is basically a zero, or very close to it, your sensors are working fine.

 

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