Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
Today, I diagnosed a toyota crown 2002 6 Piston. It has two Air fuel sensors (Upperstreams) running on 900mv. The car consumes too much fuel and makes black smoke .I checked into O2 sensors activity and found out that there are too much random activity on them like jumping from 0.17mv (lean) to 800mv (rich) while on Idle. I removed both sensors and still the scanner showing Close Loop for both sensors but the activity on them shows 0.00mv this time.
I used propane to see reaction of AFS, both go rich but response is slow.
How come , I removed two AFS sensor even the ECU cant feel it?!!!!!! No check engine light.
Any approach or idea to analyze this will be much appreciated.
How long did you run the vehicle with the O2's disconnected? Do you recall what the trims were while you were running it without the O2's? It's my experience that Toyota does not have very good oxygen sensor diagnostics, and is usually very slow to pick up on a sensor issue. My own vehicle took about 20 miles to finally set a code for a dead upstream O2. :lol: That thread is here:
By comparison, I think other makes would pick up on the same situation much faster, due to the use of bias voltages. Dodge, GM, and Honda are examples. They're likely to detect a circuit issue faster, and react with open loop or some kind of back up strategy.
