Rear O2 sensor bypass/CEL fix.

First off want to say that someone else figured this out,not my idea, but it was too good to not share on here. Back in about 04-05 I had my catalytic converter sawzall'd off and stolen. On comes the check engine light. Didn't think to much about the light being on because I knew what it was after a very short period of time. Climbing a steep grade with a load and putting more heat on the system, the light would go off. Once crested the hill and things started to cool off,,the light would come back on. Rear O2 sensor sending the signal that something was amiss. Truck never gave me any problems so no need to by a code scanner and I knew what the CEL light was from. (For the sake of arguments, lets say I had a really good idea why the light was on). Anyways,,here we go.





Radio Shack part #
1 micro farad cap 272-1055
1 mega ohm resistors 271-1134

On my truck there are 4 wires that lead to that rear O2 sensor from the connection plug at the manual transmission tail shaft. 2 black and a sold white and solid blue I split the distance in the length of those blue and white wires and cut them in two at the center. You will probably have to pull back or remove the tubing/covering that covers those wires. I slit that cover down the center with a razor to about 1/2 distance, then cut around it, removing that portion. Snip and strip back the blue and the white wire that leads forward to the connection plug,,I left the two black wires intact and connected to the sensor. The reason I cut the blue and white wires at equal lengths between connection plug and sensor,,was so that they could be easily reconnected again if needed.

As you see the pic above of the constructed Mod unito),,the right side of the unit connects to the blue wire you cut and stripped back a 1/2",,and the left connects to the white wire that you also prepared the same way. (connection plug side)

Assemble the unit as you see in the pic noticing lettering up on the blue capacitor and color rings on the resistor. Right side of assembled unit connects to the blue wire, and the left side of above pic connects to the white wire.

You can solder connections if you wish, or you can crimp connect so long as you have good crimping tools and supplys. I did a little of both. A bead of silver solder was melted by iron down into the bottoms of those crimp connectors you see above. The unit was then crimped and soldered to the prepared blue and white wires down by the sensor that lead to the plug connection

Snipped white and blue wires leading to the sensor were covered with heat shrink tube. I didn't pull any connection plug or the sensor out of the pipe,no real need because I had the wire length I needed.

Total cost to turn out the check engine light due to a rear O2 sensor code,,about $4.

Pull battery connections BEFORE you start cutting. Not a bold typed set in stone rule,,but It's the way I did it. The ECU will need a reset anyways after doing the work.

I'm no electronics expert so keep the questions with that in mind.

 

Good stuff. Might end up going this route.

 

Thanks. It's really easy and cheap and you can re connect those wires if needed.

If the CEL light stays lit after doing this, then you might have another code waiting to be read.

 

About 4 days on this,,so far no light.

 

hmmm.. my rear o2 sensor was recently broken off when a rock pushed my exhaust piping up into the bottom of my cab.. this might be a good route to take.

any idea if it will work w/ my auto trans? any difference in wiring?

 

Rock auto shows a 4 wire heated sensor,,so I think it would work. Can't say for positive because mine is manual. The part numbers don't match between yours and mine on the sensor.

Easy to slit the covering/insulation that covers the wires to the sensor and see if you have 2 black, a white and blue wire. So long as that sensor wasn't mashed heavy on the rocks, and the heated circuit on it is still good.

After some more fine print reading, I am leaning twoards that heated circuit being intact and doing it's thing at the sensor.

So far, no CEL and damned if it didn't help the idle/warmup. I am idling down in about 45sec, compared to a full minute. Might be the season change.

$4 in one hand,,and a whole bunch in the other to fix it. Pretty easy choice or check.

If you give it a shot, please say so and the outcome. Thanks all.

 

Hey, you mentioned that someone else figured this out, do you by any chance have original link? Also how is it working now? Any fuel mileage increase? Thanks.

 

I did this and didn't have any luck. Maybe someone can point out where I went wrong? FWIW I got the URD sim kit and haven't had a problem since.

And yes I taped everything up after this.

 

sub'd

 

After doing some research I'm seeing that capacitor goes between blue and white wire, resistor thought has to be on blue only below the capacitor. That could be your issue.

 

:shrug: I've had the URD sim in for over a year now. I'm not going to pull it out and try anything else. Just figured I'd share my experience.

 

Stephen, did you unplug the URD sim from the system before the adaptation for the radio shack stuff?. Never had one of those so I don't know where they plug in at.



I disco'd the radio shack setup, just to see if it kicked the cel light back on,,and it did as I kinda knew it would. Reconnected that and reset the ECM, light went out once again.

 

sub'd

 

Got mine after adding a full JBA exhaust kit, definitely going to try this!

 

Dang it, its only 1st gen isn't it.

 

Pimpin my own thread,,to keep it at the top unashamedly.

It might work with a 2nd gen,, but cant verify. A few bucks and some time is all it takes. Work smart and it a easy reversal if needed.

No codes or cel so far, still truckin along.

 

I'd be curious to see air fuels. The rear narrowband o2 sensor is used not just for cat efficiency, but to calibrate the forward primary wideband sensor on 01+ Trucks and 98 or something 4runners. That means if the solid state components are not finely selected, IMO it may be able to pass you on your cat diagnostics, but could be throwing off air fuels a bit.

 

Mod
Dumb question, but is it the blue wire that needs to go on the red stripped side of the resistor? My brain is fried from work, so I just wanted to ensure before I give it a go. Also, any noticeable loss or gain of MPG? Thanks

 

Never heard of this before. I've always heard that the rear O2 did not have any bearing on fuel trims.

 

Nope. White to the red ring,,Blue wire to the gold.

I think I gained about 2 mpg,,but still checking that. Last tank was about 1-1.75 extra mpg. Winter blend will tell the tale I think. Haven't taken any long trips yet so it's a maybe on that.

The cold idle jumps down alot quicker once running, after the install, so that might be my mpg gain right there. Fooling the back sensor/ecu into thinking all is well and then it relinquishing its hold on the idle at a faster rate than before.