I was trying to get my 96 ranger 2.3, 250K miles, smoged today,but I was told that it would fail because some of the systems are not ready. The o2 sensors, the heated o2 sensors and the cat system. I drove around for about 150 miles but it seems that the systems are still not ready. After a bit of reading I think it might be because of my oxygen sensors. From a bluetooth scanner, I could see that the upstream o2 sensors voltages are bounce between 0.2V and 0.8V, and the downstream sensor is steady at 1.275 V. Anyone know what the voltage values should be, and if replacing the sensors will allow the car to pass smog? Thanks in advance!

 

Upstream seem to be working, but all O2s only last 12 years or 100k miles, only sensors that do wear out

Downstream O2 should be steady but at 0.75-0.85v
Over 1v should set a code, and 1.275v for sure means that O2 is bad or has a shorted wire

O2s generate their own voltage using a chemical reaction with Oxygen once they are heated above 600degF(after 12 years they run out of chemicals)
0.1v is high oxygen levels, called "lean" by computer
0.9v is low oxygen levels, called "rich" by computer

0.45v is the sweet spot for best power and MPG for Upstream O2s, computer is constantly changing injector open times to keep upstream O2s with 0.45v as the average
This is why the upstream voltage changes so fast and and has a wider voltage range to get a good "average"

Cat converters heat up from exhaust temps but also by burning unburned gasoline in the exhaust, this burns up toxic gases but also burns up any left over oxygen in the exhaust
So downstream O2s tend to be steadier voltage at an average 0.8v, low oxygen levels

1986 thru 2012 Rangers all use Narrow band O2s
Later model vehicles did use wide band O2s, 0v to 5v, just FYI, in case you see conflicting voltages, wide band O2s are better when using turbo chargers which became more common in later model years

 

Could it be because the cat is bad? Or is most likely that the oxygen sensor needs to be replaced

 

At 1.275v I would replace O2 first, and check its wiring harness as best you can

If Cats are bad then downstream O2 would show voltages under 0.7v, as the Cats are not burning up enough oxygen so are not working to burn up toxic gases either

Hold on a minute
You want to be testing O2 B1 S2 on a 2.3l 4cyl engine

Hard to read the screen shot but looks like B2 S1 which a 4cyl doesn't have and that would explain the 1.275v reading

O2 sensors are designated this way
B1 = bank 1, a 4cyl engine just has 1 bank/side
B2 = bank 2, on a V6/V8 engine this is drivers side

S1 is upstream O2 near engine
S2 is downstream O2 after Cats

So a 4cyl engine would have B1 S1 and B1 S2 as its two O2 sensor

A V6/V8 single exhaust would have B1 S1, B2 S1 and B1 S2
With Dual exhaust B1 S1, B2 S1 and B1 S2 AND B2 S2

Confused, lol

Anyway check B1 S2 on your reader as the downstream O2 voltage

 

Update
Bank 1 Sensor 2 shows 0V, bought a new o2 sensor, but it still shows 0V. Doesnt matter how long I let the car run, if I rev or hit the brakes, etc.
I checked the voltage coming to the heater side of the sensor and it shows 14V so it should be fine, but when I connected the old o2 sensor and let it dangle, it didn't heat up at all. I can touch it with my hands. I connected the old sensor directly to the battery and it heats up just fine. Any reason why the sensor wouldn't accept the power coming from the connector?
Also do you know which pins on the pcm go to the sensor? I want to try a continuity test from the pcm to the sensor, but haven't been able to find the info anywhere.
Thanks

 

Yes, the O2 heaters get 12v(battery volts, so 14v engine running) with key on from fuse 20 in engine bay fuse box, they both share that one fuse and one wire, a light blue/orange wire

But the heaters are each Grounded separately by the Computer(PCM), and PCM will set a code if it doesn't see 12v on that ground wire with key on

P0135 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 1)
P0141 02 Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)

And no codes?
A heater is just a coil of wire, so 12v in = 12v out, so before PCM grounds the wire it checks to makes sure it "sees" the 12volts, if not it sets one of the codes
And it would set the code if either the 12v or the ground wire was disconnected/broken
Leave the O2 unplug and start engine, should get CEL pretty fast, just a "sanity test" for PCM

What does B1 S1 show with key on?
B1 S2 should be the same on cold start

PCM also has these codes for B1 S2, the oxygen sensor only part, not heater part
P0136 02 Sensor Circuit Malfunction (Bank I Sensor 2)
P0137 02 Sensor Circuit Low Voltage (Bank I Sensor 2)
P0138 02 Sensor Circuit High Voltage (Bank I Sensor 2)
P0139 02 Sensor Circuit Slow Response (Bank 1 Sensor 2)
P0140 02 Sensor Circuit No Activity Detected (Bank 1 Sensor 2)

So if a wires was bad it would set a code, for sure

 

Does fuse 20 for sure control both o2 heaters? I disconnected it to see which check engine codes I get but I only got a code for the upstream heater. P0135.

 

Go here: https://www.ranger-forums.com/genera...1-models-3747/

Get your 1996 Owners manual

Page 314

Engine fuse box
Left hand side HEGO is the O2 heater fuse, looks like a 15amp fuse in that diagram

HEGO = heated exhaust gas oxygen "sensor"

 

I see, so fuse controls both heaters. Since the pcm only sends one error code for the upstream oxygen sensor, is it likely that the pcm is bad? Any way to know for sure?
Back to the original question, I’ve driven the car over 500 miles and still haven’t been able to set any of the monitors. I figure if the computer is bad, doesn’t matter how much driving you do. It won’t set the monitors

 

Yes,could be bad computer if its not setting codes and you can't get P1000 to go away

Here is a step by step to help clear P1000: https://www.totalcardiagnostics.com/...-driving-cycle