Now, from what I understand from you guys and other sources, is that if you unplug a properly working sensor, the idle should be effected. So, here's my situation.
Before sensor replacement:
I had unplugged the sensor and driven the vehicle for a number of days in this state. It seemed to run fine, but I wanted to make sure all was as it should be, so I replaced the sensor and hooked everything back up (had the battery disconnected during the replacement - to reset the ECU - if necessary).
After sensor replacement:
The vehicle again seems to run fine, BUT.... if I go and unplug the sensor once the engine is warm, nothing changes. The idle stays the same - from what I can tell.
Is this normal? Or is the computer still not registering the new sensor?
I know I could just leave it at this, but I don't want to be running lean/rich and burning more fuel than I need to or burning out the cat. Any thoughts would be great.
I think the idle would stay the same, it's the ecu that is compensating for no reading from the sensor by staying in open loop. Please correct me if I'm off here.
Originally posted by mookie I think the idle would stay the same, it's the ecu that is compensating for no reading from the sensor by staying in open loop. Please correct me if I'm off here.
But my repair manual says that this is the way to check for a bad sensor - to disconnect the sensor once the engine is at operating temp. If the engine idle changes, the sensor is working - if it doesn't change, the sensor is bad.
Well, my sensor is obviously new - so what (if anything) is going on???
There should be a way to go into a diagnostic using the screw on your ECU. When it's in this mode you can count the flashes of the "Check Engine" light and that will tell you how many times the O2 sensor is flipping (lean/rich/lean/rich) in a set time.
Maybe your manual has the instructions? If not someone here should be able to walk you through it... You can also check codes this way. Pre OBDII (1995 and earlier) vechicles, at least in the USA don't turn on the "Check Engine" light for as many things as later models, so you need to check for other failures from time to time, even if the CEL isn't on.
Heath
__________________ 1997 Nissan XE Truck - 133,000 Miles
1990 Infiniti Q45 - 91,000 Miles
2005 Infiniti G35 Sedan - 34,000 Miles
Heath is right -- check the PCM using the instructions found in the sticky above.
The O2 sensor may or may not be used at idle. Remember, an O2 sensor has to be HOT to produce any voltage potential (at least about 600 degrees F). Usually at idle, your exhaust temperature is near that reading, so on a cold day perhaps, even after the engine is "warmed up", the exhaust temperature could still be below the O2 sensor's threshold for operation, which the computer knows is normal. This is why many newer vehicles use heated O2 sensors -- to provide readings all the time, even at idle (because the heater keeps the sensor at or above 600 degrees F).
The only real way to check if the sensor is operating is to keep it plugged in and monitor its signal when you're driving. This is done either with a voltmeter (see http://jadcock.oldsgmail.com/o2tapper/ for a solution I made for a different vehicle) or use the PCM's lights to monitor the cross-counts, which is when the voltage cross the stochiometric voltage of around 450 mV. I think the cross-count number should be at least 10 in 5 seconds or something? Your book should say how many your vehicle should be producing. On my old Cutlass, it was about 2 cross-counts per second, but the Nissan computer may operate differently than my Oldsmobile did. Consult your manual to verify how many cross-counts you should be reading.
Sorry for being a bit of a dummy on this. I know my way around vehicles pretty good, but some of this computer stuff is less straight forward.
I'm thinking my sensor should work at idle - it is a 3-wire (heated, I'm guessing) sensor. And I don't know if my '92 pathfinder has a engine light - never seen it.
Jadcock - your link to the O2tapper didn't work for me.
So, could someone please give me some detailed instructions here (aka: hold my hand). Including explanations of the acronyms (sp) such as PCM, etc. and where to find these things.
Sorry for all the questions - Thanks again for all your help.
Your vehicle should have a check engine light. I had the same question about mine (does it have one?) until I removed the gauge cluster and found that the light and the socket had been removed by a previous owner...presumably to sell the vehicle. This may be the case with yours (the light having been removed).
Regardless, I find it curious that yours has a 3-wire sensor. Mine (a '95 4-cyl) only has a one wire, which was the norm until the past decade. Maybe the V6 engines do have 3-wire sensors and the PCM is calibrated differently. There are many different acronyms for the engine/powertrain computer, and the term you use depends on what you're used to using.
PCM = Powertrain Control Module
ECM = Engine Control Module
For this application, you (I) would really be more correct calling the computer an ECM, since it really only controls the engine. In other modern vehicles, the engine controls the engine and transmission, and is referred to as a PCM, since it controls the whole powertrain.
On my truck, the ECM is underneath of the passenger seat. I removed the seat to access it, since the screw you use to change modes points toward the transmission tunnel...completely inaccessible with the seat installed.
View and print the sticky post under "From your friendly moderator". The message from Tolleyy explains the process on the 91-95 Hardbody and Pathfinder. It's fool proof as long as you go step-by-step. You can't mess anything up.
That link is correct...but it looks like the server my homepage is on is down. Nuts.
Linear Mode
