Working on my pastor’s 2008 Tacoma 2.7L with 77,000 miles, and getting a bit stumped. He just bought this truck, and on the way home the check engine light came on. Had the code read, and it was:
P0138- O2 Sensor Circuit High Voltage (Bank 1, Sensor 2).
He replaced the O2 sensor, the EFI relay, had the code cleared, and a less than 100 miles later the check engine light came back on- this time:
P0136- Oxygen Sensor Circuit Malfunction (Bank 1, Sensor 2.) This code is currently active, and also pending.
This is when he called me, and I am a bit stumped- because as best as I can tell from my scanner, the o2 sensor is operating as it should. (this Toyota has an upstream Air/Fuel Ratio Sensor, and a downstream Oxygen Sensor)
the “book” says at steady, warmed up idle
-upstream sensor should read at 3.3volts. I show 3.4volts
-downstream sensor should read between 100 mV and 1000mV. I show about 800-900mV, with it decreasing as expected immediately after releasing the throttle and idle drops. After I goose the throttle and let off quick, it does drop below 100mV, but only for a second or two- then it climbs back up to 800-900mV.
-downstream sensor should read above 5 ohms. I show over 5ohms constantly (usually somewhere around 200ohms)
-Fuel trims are good: usually about 5 numbers apart (ST reading about 0 to -2, LT reading around 3 or 4.)
I did a smoke test on the intake, and found no leaks. I have done a visual on the exhaust, and didn’t see anything that looks like it’s a leak. Even thought the p0136 is active, there is no freeze frame data to be found, so I can’t see if I have an intermittent drop out of some of the readings.
I don’t deal much with gasoline emissions issues, and deal even less with Toyota’s (although my son did just buy one, lol, so it is in my future,) so any guidance/input/direction would be appreciated.
