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Open Loop Fault Hello Everyone, I'm new to posting, please excuse my forum etiquette. I have 2002 Civic LX Standard 4dr It's running in Open Loop-Fault - No fuel trims - No O2 Sensor Readings *** I do have power&ground to heater wires*** It runs and drives fine, but I can't seem to figure out what's wrong. Any help is appreciated. |
Re: Open Loop Fault And what happened when you plugged it into a code reader.. I suspect you tried and got no connection as the ECU is blown. |
Re: Open Loop Fault I have the exact same codes. O2 sensor heater circuit and heater main relay. My my code scanner does reed live data and showing activity on all PIds, except LTFT&STFT |
Re: Open Loop Fault Post your fault code numbers. And if your reader displays it, post the freeze frame data. |
Re: Open Loop Fault https://cimg5.ibsrv.net/gimg/www.civ...c62293e52b.jpgThis code pops up every time. Even after disconnecting the batter or erasing the codes with my OBD2. https://cimg8.ibsrv.net/gimg/www.civ...5ad3fa8747.jpg https://cimg4.ibsrv.net/gimg/www.civ...f77a7489b.jpeg |
Re: Open Loop Fault I KNOW you posted a picture but I can't see it in the post P0135....you confirmed power and ground to the sensor heater? Replace the front O2 sensor I always recommend DENSO or NTK brand-- whichever brand was originally installed by the factory |
Re: Open Loop Fault I have replace both o2 sensors, with OEM replacements. I’ve also checked heater power and heater ground on both sensor. They are good. I have ave the same readings with new sensors. Please note: the only time I get upstream activity, is when the following is down. Quick throttle the upstream goes lean. Then gradually goes back to .9V. and I unplugged 1 injector connector, idle gets rough and upstream starts isolating up and down, as it should during normal operation |
Re: Open Loop Fault Front sensor: Check resistance of the heater |
Re: Open Loop Fault Upstream resistance was 3.6ohms. Same as old,but I changed anyway. Same readings on OBD2 |
Re: Open Loop Fault Can some confirm that I checked my engine side connector correctly? Looking at the connect, bottom right pin, testing for 12v. I used my battery for ground and found 12v at the pin. Looking at at the connector, bottom left pin, testing for heater ground to ecm, I used the battery as my positive, and pinned the looking for ground. Was this his a good wire integrity test? |
Re: Open Loop Fault
Originally Posted by 2002CivicTDA
(Post 4743727)
Can some confirm that I checked my engine side connector correctly? Looking at the connect, bottom right pin, testing for 12v. I used my battery for ground and found 12v at the pin. Looking at at the connector, bottom left pin, testing for heater ground to ecm, I used the battery as my positive, and pinned the looking for ground. Was this his a good wire integrity test? You can't just go poking at the wiring for any old ground. You need an accurate wiring diagram and to follow wire colors to make sure of which circuit you are testing. OR if you match up the harness with the like colored pair of sensor heater wires, that can work too as long as nobody ever hacked up the engines harness connector. If you tested/found the sensor ground and just assumed that's the ground for the heater circuit, that's incorrect. B+ for the O2 heater circuit (blk/yel) comes from fuse #4. There is no heater relay. Ground for the heater is controlled and monitored by the PCM (blk/wht). It is not grounded until the engine is started and the PCM turns it on. The heater is run and tested after startup--and if the self test fails (5 seconds), the PCM then turns off the heater for the remainder of the run time and illuminates the CEL on the dash. |
Re: Open Loop Fault Yes sir... I did use a wiring diagram I found online. It seemed to me correct, per your description. Mare there any specific reasons why the system would be in “Open Loop-Fault”, assuming the o2 sensors and it’s witing are good? |
Re: Open Loop Fault Open loop fault is just a fuel control status, not a code.........likely you see it because the PCM is disregarding the primary O2 sensor due to the P0135 code, thus, open loop. |
Re: Open Loop Fault What do you recommend I check? I’ve peaked my diagnostic abilities on my own. |
Re: Open Loop Fault To check if the PCM is in fact controlling ground to the heater...... Sensor connected like normal: 1 Voltmeter connected to battery ground 2 Backprobe the blk/wht wire, (I might do this at the PCM in the dash instead of the engine compartment harness) 3 Key on 4 Should read battery voltage (Here I'm assuming the PCM won't ground it until the engine is started) 5 Start engine 6 should read 0v as long as the PCM is providing ground to the heater circuit (Some PCMs can modulate the current, so those wouldn't necessarily show full ground on the meter) |
Re: Open Loop Fault It’s reading 5.6mV vehicle running. 3.3 mV KOEO |
Re: Open Loop Fault 3.3 mV KOEO I'd guess either you didn't get a good contact in the backprobe, or the blk/wht line is grounded for some reason.....or you're losing the B+ somewhere between the #4 fuse and the sensor KOEO backprobe the blk/yel wire, make sure it has 12v+, backprobe the sensor side of the connector on the same circuit to verify that 12v didn't get lost inside the connector (bad terminal contact) How about you unplug the PCM and try this again KOEO voltage check on the blk/wht wire (backprobed with the O2 sensor connected)....that should eliminate the PCM grounding internally Also check if the wire is somehow grounded in he harness.... |
Re: Open Loop Fault I really appreciate your help. I might have to look for an ECU pin out, before I continue. I locateded the blk w/yellow strip, using point to point continuity test. But I can’t locate the blk w/white wireusing the same method |
Re: Open Loop Fault Doesn't the diagram you found show the B/W at the PCM connector? O2 B1S1 B/W wire @ PCM is connector A cavity 1 |
Re: Open Loop Fault I’ll start back tomorrow. ill also find a ecu pin out. |
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