#1
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Sentra 1.8S Stuck in Open Loop Mode, No DTC
I posted the following issue to b15sentra.net as well -- hopefully someone has had a similar problem and can offer advice!
So I recently got a WiFi OBD-II adapter and the "OBDCarDoctor" iPhone app to help me troubleshoot some issues with a friend's Jeep. There seemed to be O2 sensor issues, and I thought, let me compare the o2 sensor waveform with that of my perfectly running Sentra and see what the difference is. Well I was surprised to see that the Band 1 Sensor 1 O2 sensor voltage was hovering around 0.3V and not oscillating. On the highway it would sometimes go lean (~0.1 or 0.2V) and sometimes rich (0.7 or 0.8) but most of the time it was hovering around 0.3V or drifting, and not oscillating at all. I believe the "Fuel System Status" read Closed Loop, which is baffling, but maybe I am remembering wrong. Again, no DTCs (except for P0455 which I later fixed). Note that the car had just passed NY State emissions inspection a couple of weeks prior. So today I finally got around to replacing the upstream o2 sensor with a Bosch 13565 (I believe the previously installed one was the same type as it looked identical). And after starting the car, the o2 voltage still hovers at 0.3V at idle. However now, the fuel system status goes right to "Open Loop Mode - System Failure" with a couple seconds of starting. Again, no DTCs whatsoever. I disconnected the battery for an hour to try and clear the ECM, but no change. Does anyone have any idea what could cause this? One would think that if the system was defaulting to Open Loop mode due to a system fault, that there would be a reported system fault. I did notice that while driving the voltage reading often dips below 0.2V, but rarely goes above 0.31V (though it did get to 0.8 once or twice). This has me thinking that maybe a ground could be missing? But even if the o2 sensor wasn't behaving correctly, how would the ECM know so quickly after start up, and if it did know, why is there no DTC? Another part of me is wondering if this weird behavior is due to having the diagnostic tool connected. Its a frustrating situation since I want to get the best MPG I can with this car, but I don't want an expensive situation at the dealer when on the surface everything is working perfectly. Sorry for the wordy post -- any thoughts on this matter would be greatly appreciated! My next steps are going to be 1) measure o2 sensor voltage at the connector and confirm they resemble those reported by the ECM, and 2) see if the o2 sensor ground is tied to the chassis. |
#2
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Update
Update: This morning I checked the codes again, and it had a pending P1031 (Air Fuel Ratio Sensor 1 Heater Control Circuit Low Bank 1). So maybe it was detecting that at startup leading to the Open Loop System Failure condition, but for some reason, wasn't updating the DTC list?
I'm going to check the heater voltage and other connections to the sensor when I get the chance... still doesn't make total sense, but having a DTC pop up is giving me some hope. |
#3
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1. verify Bosch part #13565 Upstream A/F ratio sensor for your '04 Sentra. you can do your research at rockauto.com;
2. System in Open Loop - at cold start by default ECM ignores sensor feedback until engine reaches normal operating temp. when it takes longer to reach NOT, ECM decides to trigger a code either faulty T-stat or ECT sensor. 3. System in Close Loop - ECM is receiving sensor feedback and comparing data in its Look Up table or drive map and make adjustments to get desired results. Also read up and understand Fuel Trim. happy Troubleshooting. |
#4
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Thanks for your response! Actually I typed the wrong sensor number, it was Bosch #17179 and yes I've verified it is correct.
I monitored that fuel status from a cold start, and it starts out saying "Open Loop -- Insufficient operating temperature" for about 5 seconds, and then switches right to "Open Loop - system failure". I am becoming more and more convinced that it is a detected wiring issue that just isn't bubbling up to a DTC. I grabbed the P1031 diagnostic procedure from the service manual and will test that out, it sounds fairly straightforward. I'll update this thread with the results. |
Tags |
18s, dtc, loop, mode, open, oxygen, sensor, sentra, stuck |
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