How to reset ECU? - limp mode (O2 sensor unplugged)

[elpiar]

Hi,

I replaced my stock o2 sensor with PLX wideband o2 sensor in preparation to boost my car and tuning. My plx controller has both wideband output 0-5v and narrowband output 0-1v for the ECU.

It ran great for a couple days, and then i accidentally mess the jumbled wires in the ECU area and disconnected the o2 sensor wire. The ECU goes into limp mode (very rich and rev limit at 2.5k)

Anybody has any idea how to reset the ECU? I tried unplugging the power from it but it doesn't fix it.

[s14_240sx]

The ecu wont go into limp mode if you disconnect the O2 sensor. Seems more like you diconnected your maf wire.

[sohcistehsex]

yeah your mafs is either bad or unpluged

[Kouki Chick]

Factory ECU can be reset by pulling the fuse.

[sharkerio_coupe]

Factory ECU can be reset by pulling the fuse.

might sound retarted...i don't care. But, which is the correct fuse to pull?! wouah, i think this might solve my problem...

-my MAF wire was torn (does that count as unplugged?)-i soldered it back-symptoms improved, but idle is still junky-i was told its prob in limp mode....-any who, so i'd like to reset my factory ecu...which fuse

does this sound like it should work???

[Silvia007]

You pull the battery and step on the brakes to drain all power from the system. Or you can just pull the ecu and there's a little knob that you can turn on the ECU itself.

[sharkerio_coupe]

tried i all and still nothing...

disconnected the battery, and did the break thing. it did turn off the cell turned off. the symptoms remained the same. then after a bit the cell turned back on.

the car runs rich, i get black smoke out the tell pipe...in now revs passed 2500 so i don't think it the maf anymore, plus i unplugged it and ran it on my friend car and it ran fine. Teh ECU continues to send out code 12 though.

i replaced my o2 sensor and tried to reset the ecu again, both by battery unplug and the ecu screw...nothing. i was thinking the distributor??? idk...i keep guessing and spending....i dropped it off today for a proffesional to take a look at it.

[Shusaka]

if it is a twin cam ecu, then here is how to clear the ecu:Step 1. turn your ignition on but do not start the engine.Step 2. turn the screw on the side of the ecu to diagnostic mode(all the way clockwise)and wait for 2 secondsStep 3. turn the screw back fully counter clockwise, wait 30 secondsStep 4. Turn the screw fully clockwise again and wait 5 secondsStep 5. turn screw back fully counter clockwise wait 3 seconds and start your engine, let it run for at least 15 secondsStep 6. turn your car off and wait 10 seconds then repeat steps 1 and 2 after step 2 is repeated look inside your ecu's diagnostic window and watch the red led, it should flash code 55, five long flashes and five short flashes ( _ _ _ _ _ -----) this is your all clear code and you should be good to go or your money back

[mrog71]

So on my 2000 maxima, there are 2 holes on the driver side of the ecu. I can't see inside very far - is the screw to reset the ecu recessed inside one of those holes (which were taped over)? I don't want to stick my screwdriver in there and screw something up...

thanks!

[Shusaka]

yeah that would be a bad idea and nothing but bad juju could come from that action with the holes and the screwdriver and the short circuiting!!! anyways i apologize for my simpsons professor frink reference to all of you who have no sense of humor, and now on to a more logical answer to your question. on a 2000 maxima you should have obdII which means a simple code reader should clear your peoblems and its only like a $39.99 trip to autozone as opposed to a $1500 trip to nissan to have them replace your ECU. On the 240SX all but the kouki and very select zenki models were obdI which is why we even have that screw there to begin with. to simplify this think of the screw on our ecu's as your $39.99 code reader, that screw will allow a small red led to flash us a code telling us our problem which we have to look up online to figure out, your code reader does this much quicker and more efficiently, so purchase the code reader and just make life easier, BTW 1995 240SX = OBD-I, screw yalls OBD-II Couch

[240man91]

if it is a twin cam ecu, then here is how to clear the ecu:
Step 1. turn your ignition on but do not start the engine.
Step 2. turn the screw on the side of the ecu to diagnostic mode(all the way clockwise)
and wait for 2 seconds
Step 3. turn the screw back fully counter clockwise, wait 30 seconds
Step 4. Turn the screw fully clockwise again and wait 5 seconds
Step 5. turn screw back fully counter clockwise wait 3 seconds and start your engine, let it run for at least 15 seconds
Step 6. turn your car off and wait 10 seconds then repeat steps 1 and 2 after step 2 is repeated look inside your ecu's diagnostic window and watch the red led, it should flash code 55, five long flashes and five short flashes ( _ _ _ _ _ -----) this is your all clear code and you should be good to go or your money back



great right up man ;p