My check engine light recently came on. I used a OBD reader to retrieve the code P1135 as well as the following "Inspection/Maintenance" (I/M) reads:

3 Incomplete I/M monitors: Catylist, Evap, 02 Sensor
4 Complete I/M monitors: misfire, fuel, comp (comprehensive components), and finally, O2 Htr.

So far I have cleaned the MAF sensor, and checked the upstream and downstream 02 sensors.

Cleaning the MAF sensor didn't help anything. I cleared the codes afterwards and they all promtly came back.

Before I get into my 02 sensor results let me explain how the 02 sensors are supposed to work according to my haynes repair manual. When the car is started, a digital multimeter should read 0.1 - 0.2 V coming out of the sensor, which is during open loop mode. After about 2 minutes the sensor is supposed to shift between 0.1 to 0.9 V.

I got some wierd results when I checked the 02 sensors:
The downstream sensor htr circuit has a resistance of 14 ohm which is within spec. The Htr circuit gets 12Volts, which I assume is right. But when I backpinned the 02 sensor output and started the car the voltage quickly jumped up to a tad above 0.9 V (~0.92V) then after a minute or so rapidly dropped to 0.060V. The output stayed pegged at 0.06V for about 5 minutes.

When I checked the upstream 02 sensor the resistance of the htr circuit was open (infinity), which is out of spec. Also, the heater voltage is 9V! I'm confused about that because the wiring diagram I have shows the htr voltage for both the upstream and downstream 02 sensors coming from the same place. The implication is there is a bad connection somewhere in the upstream 02 sensor wiring harness causing a Voltage drop. When I checked the 02 sensor voltage output I got a pretty much constant 0.5V output while the truck was running.

So...It appears that both sensors may be bad. Could 2 bad 02 sensors be causing all the other codes that I read? Btw, my truck has 115,000 miles on it.

 

Your first sensor isnt an o2 sensor. Its whats called an air/fuel sensor. It does the same job as an o2 sensor but its considered a wideband sensor and operates differently voltage wise than on o2 sensor. Replace your 1st sensor with the correct denso A/F sensor and you should be back in business.

As far as the incomplete monitors, you need to have a couple complete drive cycles for the monitors to reset themselves. They will be incomplete when you have a check eng lite or when you clear the codes or batt is dis connected. Once you replace your a/f sensor, clear the code, drive the truck a couple days, everything should be ok

 

Thanks I'll try that. I didn't know that the upstream "air/fuel" sensor had a different output. The haynes repair manual sometimes seems to be incomplete.

 

you just need to replace the bank 1 sensor 1. which is the before cat air fuel sensor.

 

o2 sensors have a sweeping voltage when its operating properly. if you looked at it on a graph, it would be a rapid up and down sweeping line. An a/f sensor holds close to one voltage once at operating temp. I think its like .33V, Im not exactly sure since I dont have my reference material here. That kind of stuff is best looked at from a factory manual. you sometimes need to take the haynes and chiltens manuals with a grain of salt

 

a/f sensor stays at .65 nominal volts. you need to watch it's waveform which is calculated inside the ecu. unless your obd II scanner can specifically read the waveform no way to t-shoot an af sensor


p1135 is the air fuel sensor heater is junk. it is a dead on code.
your a/f sensor 100% absolutely is porked and you need a new one. (unless the wiring harness is junk)

also do not bother with getting an air fuel sensor anywhere but a toyota dealer.