# 2008 Tacoma- p0136, but everything looks fine? **URL:** \ **Category:** Maintenance/Repairs\ **Tags:** tacoma, emissions, toyota\ **Created:** [November 30, 2020, 8:24pm UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851 "2020-11-30T20:24:46Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [November 30, 2020, 8:24pm UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851/1 "2020-11-30T20:24:46Z")
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. ---
**Author:** ![Mustangman](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/mustangman/32/44130_2.png) [@Mustangman](https://community.cartalk.com/u/Mustangman)\ **Post date:** [November 30, 2020, 10:00pm UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851/2 "2020-11-30T22:00:28Z")
That code P0136 code indicates it might be a bad harness or connector. Depending on the frame update rate of your scanner, you might not be seeing a drop-out or intermittent signal from the sensor. Maybe check the connector for corrosion and the wiring harness for damage as a first step. ---
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [November 30, 2020, 10:15pm UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851/3 "2020-11-30T22:15:10Z")
I checked the connector (component and harness sides,) and didn’t see anything. All looked clean and shiny. I will reverify. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [November 30, 2020, 11:19pm UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851/4 "2020-11-30T23:19:27Z")
> [@eddo](#): > > I show about 800-900mV, That center point is too high, indicating that the fuel system is rich. Both P0136 and P0138 can be caused by a failing air/fuel sensor. Are the fuel trims out of the normal range? ---
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [December 1, 2020, 1:08am UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851/5 "2020-12-01T01:08:35Z")
it is on the high side, but from what I am reading, still within specs, is it not? Fuel trims seem good: usually about 5 numbers apart (ST reading about 0 to -2, LT reading around 3 or 4.) ---
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [December 1, 2020, 4:13pm UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851/6 "2020-12-01T16:13:23Z")
Here are some snapshots I took last night after my drive home. Does this help any? ![1](https://global.discourse-cdn.com/cartalk/original/3X/6/3/63ac7bbceca3f3f2e2dbb4fa7444e5b374170078.jpeg) ![2](https://global.discourse-cdn.com/cartalk/original/3X/1/9/1951dc8a8894acaf3bf7f9dac71d1ce1b5d2164a.jpeg) ![3](https://global.discourse-cdn.com/cartalk/original/3X/0/0/004f2efc57707d48608e48df6fd167b8a68ba1b7.jpeg) ![4](https://global.discourse-cdn.com/cartalk/original/3X/d/7/d76ed9935a7435d42daaa54d2e5b0c3020bb3622.jpeg) ---
**Author:** ![eddo](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/eddo/32/2594_2.png) [@eddo](https://community.cartalk.com/u/eddo)\ **Post date:** [December 2, 2020, 8:04pm UTC](https://community.cartalk.com/t/2008-tacoma-p0136-but-everything-looks-fine/172851/7 "2020-12-02T20:04:08Z")
> [@Nevada\_545](#): > > > [@eddo](#): > > > > I show about 800-900mV, > > That center point is too high, indicating that the fuel system is rich. > > Both P0136 and P0138 can be caused by a failing air/fuel sensor. I think you got it. I went ahead and replaced the AFR, and the code has not returned- even in a long drive on Test Mode. here is after numbers- o2 voltage came way down at idle. ![5](https://global.discourse-cdn.com/cartalk/original/3X/d/9/d9574aa2bd1bc0c5c75016c8e75232725984279e.jpeg)