Oxygen sensor not reading...cause or effect?
Could be either, probably effect, but it could also be both, what with the way everything is interconnected on these things.
Seems I remember watching it noting a sticky output before, what's a sprinter use O2 for?
The O2 sensor is mounted in the exhaust manifold to monitor how much unburned oxygen is in the exhaust as the exhaust exits the engine. Monitoring oxygen levels in the exhaust is a way of gauging the fuel mixture. It tells the computer if the fuel mixture is burning too rich (less oxygen) or too lean (more oxygen). The computer uses the oxygen sensor's input to regulate the fuel mixture, which is referred to as the fuel "feedback control loop." The computer takes its cues from the O2 sensor and responds by changing the fuel mixture. This produces a corresponding change in the O2 sensor reading. This is referred to as "closed loop" operation because the computer is using the O2 sensor's input to regulate the fuel mixture. The result is a constant flip-flop back and forth from rich to lean which allows the catalytic converter to operate at peak efficiency while keeping the average overall fuel mixture in proper balance to minimize emissions. It's a complicated setup but it works.
Then throw in the EGR valve, which recirculates a portion of the engine's exhaust gas back to the engine cylinders, which dilutes the O2 in the incoming air stream and provides gases inert to combustion to act as absorbents of combustion heat to reduce peak in-cylinder temperatures, which lowers the NOx.
Add to that the Mass Airflow Sensor which measures the amount of air intake into the engine, and the Air Temperature Sensor (cold air is more dense than is warm air) and if any one of these things is malfunctioning it could cause any one of the others to throw a code, which may or may not be the actual problem.
That's why the Low Boost Pressure error code, which puts you into LHM, can be do frustrating. You're like, "Well duh, I can see that there's low boost pressure, idiot, now tell me WHY." There are dozens of things that can put you into LHM. The chances are if it's an EGR error code, it's probably an EGR valve, as they seem to last about 300,000 miles give or take. But it could be that big honkin' metal thing the EGR directs gases into, which can get clogged up, restricting the air intake and throwing an EGR code. Or a cracked hose or fitting, or a missing valve stem cap.
