1997 Volvo 850, n/a, Closed Loop Fault

I can't get the car to do anything but go from open loop directly to C_L Fault. The upstream oxygen sensor is brand new Bosch, correct OE part. The temperature sensor operates correctly, the engine has no fault codes in about 100 miles of driving, long term fuel trim is a little rich (-3.5) but nothing that would be all that unusual when running in open loop. Ideas?

Upstream sensor voltage readings swing as low as .170 under brief acceleration, up to about .805. Low at idle is about .230 or so, with an occasional drop beneath .2. Is that too wide of a swing? If so, what could cause that?

What factors go into a closed loop FAULT? My understanding is that if the oxygen sensor is sending signals that aren't out of range, and if the coolant temperature is sufficient, closed loop operation should commence.

I'm about to give up on it...

What’s the rear o2 sensor doing?

Does it run bad?

With this model there is no way to see that. Only the front is visible as far as I know (and others far more knowledgeable than I) have said.

It runs fine, Cheryl. My headache is that the car can't go through NYS inspection with almost all of its "systems" listed as Incomplete, and none of the system tests will run when the car has a closed loop fault and doesn't enter open loop operation. The car had 1001 Diagnostic Trouble Codes when I got it; I cleared them and replaced the rusted-out catalytic converter with a new, higher-end unit, and fixed loads of vacuum leaks, an EVAP leak, plus installed new wires, cap, rotor, etc. I just don't get what could be wrong! It seems to me that the 'fault' part means something, as opposed to the car's simply staying in open loop mode. But much of this is very mysterious to me!

Clear codes and inspect. No worries about readiness for the 96-98 volvos in NYS.

Are you sure of that, Fudgie? I've heard that California's smog checks are pretty lenient on '96 turbos, but are New York's that understanding? Will I have to speak to the inspector about it or is that automatic? I'd love it if so!

Inspect it. It will go through no issue. If the DMV machine doesn't like what it see's it will fail it. No biggie. Just clear the light right before you plug it in. Volvos of that generation had an issue with key off power if I remember right. Every time you turn it off monitors would reset

I trotted down to the mechanic I use and he had run out of stickers. But he assured me that nothing will pass without a certain number of readiness programs having run. Are you certain that there is an exception for '97 850s? I am still trying to figure out what could be preventing this thing from going into open loop. The mechanic said a pending code can prevent it, but I checked, and the car has no pending codes. I am baffled!!

New York inspection website says at least 25 years old for emissions exemption:

I have little experience with those cars, but the keep alive memory issue that Fudgie mentioned sounds plausible.

For giggles if it was my headache, I would try to disconnect the battery and hold the positive and negative cables to each other for a minute to give the pcm a "hard reset" (capacitive discharge).

Good luck!

What kind of numbers is the coolant temperature sensor showing from a cold start to full warm up - thinking default strategy
.

Yes. I am certain. Make sure the check engine light is off and inspect it. Rules don't apply to those old Volvos in NYS.

Temperature readings are just what they should be, in Celsius of course, but accurate ambient temperature at start up and the numbers climb appropriately until close to 100C (212F).

I'll go down this morning and report back in a few hours! Thank you for the confidence, Fudgie!

Success?

Perfect success! You are a genius my friend! Only three completes--the ones that always are that way the moment the engine is started--and like 9 INCs. No MIL, though, and the inspection went perfectly! It's on the road and with a nice red sticker! Thank you so much!