How does the O2 sensor heated circuit function?

[sierradmax]

Anyone have the knowledge to understand it's operation and can describe it in layman's terms?

I know there's a TSB for the issue related to the 05-06's but my 05 has been on the road, able to pass until now. Before I perform TSB 25-005-13, I'd like to see if there's something else I can check or resolve.

in September of 19', I finally put the Jeep back on the road after a full rebuild, new O2's, injectors, Cat's, and just about every sensor was replaced. I remember having 2 "not ready's" for emissions testing but after driving about 200 miles, only 1 was showing and it was able to pass. Now, I have had the same two but I'm well over 300 miles since I checked and I still am showing two "not ready" yet no codes.

 

[L J]

Which monitors are not ready?

 

[sierradmax]

Which monitors are not ready?

O2 sensor heater and Evap monitor

 

[SvtLdr]

I'm by no means an expert, but I'll give it a go. O2 sensors need to be warmed up in order to function properly. The hot exhaust gasses do a good job of that in warm temperatures. The O2 heater circuit is designed to warm up the sensor rapidly (faster than the exhaust would on a cold day) in order to get the sensor functioning properly and communicating with the ECU. This is all in the name of emission control and fuel economy.

 

[RMETeeJay]

What @SvtLdr said. Earlier, unheated sensors will eventually get up to temp (600 degrees), but uses more fuel and emits more gases until then. AFAIK, a resistor in the heated sensor wiring tells the computer when it's up to temp.

Did you use the recommended brand/model O2 sensors? https://wranglertjforum.com/threads/the-official-jeep-wrangler-tj-oxygen-o2-sensor-thread.4068/

Are the grounds for the O2 sensors' circuit solid?

 

[sierradmax]

Yes, all new NGK sensors were used. I'll check grounds and I think my scan took can measure all sensors

 

[pagrey]

A single cold start will clear EVAP if you don't have a leak, no codes and EVAP not passing after a cold start means you have that TSB or PCM issues. You also need between 1/4 and 3/4 tank of gas for it to run the EVAP test so make sure you have some gas but not a full tank.

 

[sierradmax]

What @SvtLdr said. Earlier, unheated sensors will eventually get up to temp (600 degrees), but uses more fuel and emits more gases until then. AFAIK, a resistor in the heated sensor wiring tells the computer when it's up to temp.

Did you use the recommended brand/model O2 sensors? https://wranglertjforum.com/threads/the-official-jeep-wrangler-tj-oxygen-o2-sensor-thread.4068/

Are the grounds for the O2 sensors' circuit solid?

O2 grounds are good. I drove around a bit with my scan tool. Sensors are reading but it's tough to understand what is closed & open loop. I did notice intake temps hover between 85 degF and 100 degF while the coolant stays pretty consistent at 194 degF. Those values, IMO, are a little low?

 

[SvtLdr]

It is normal for the ECU to cycle between closed/ open loop depending on driving conditions (i.e. throttle input, temps, etc.)

Those intake temps seem normal to me. Keep in mind that intake temps should normally be lower than your coolant temp after the engine is warmed up and in closed loop. What was the ambient air temp when you were driving around?

 

[sierradmax]

temps were in the low 60's

 

[RMETeeJay]

That coolant temp is a bit low (assuming you were fully warmed up?). What codes are you getting?

 

[sierradmax]

That coolant temp is a bit low (assuming you were fully warmed up?). What codes are you getting?

Post #1. No codes.

 

[pagrey]

It is normal for the ECU to cycle between closed/ open loop depending on driving conditions (i.e. throttle input, temps, etc.)

I don't think so, once the O2 sensors are up it doesn't go back. After a minute or so the O2 sensors should give reliable readings and it shouldn't go back to open.

 

[SvtLdr]

I don't think so, once the O2 sensors are up it doesn't go back. After a minute or so the O2 sensors should give reliable readings and it shouldn't go back to open.

I was under the impression that nailing the throttle will send the ECU back to open loop momentarily to make as much power as it can? Perhaps I am misinformed.

 

[RMETeeJay]

Post #1. No codes.

Sorry, I did read that initially but forgot.

I would maybe reach out to @Wranglerfix for advice before doing the TSB. He has a ton of experience dealing with the 05-06 computers, etc. One thing I'd be asking myself is why didn't it happen before the full rebuild? I would go over any wiring touched during the rebuild with a fine tooth comb, unplug the connectors from the ECM and securely replug, etc.

 

[sierradmax]

Well, I gave in and performed the TSB. Drove 5 miles, filled the tank to 3/4, then drove back to my shop. Let it idle and checked with a scanner. All emissions are now "complete". Go figure..