Another CEL Thread!!! P0138 and P2195

First check all wiring. On my RAV4, the A/F sensor wires have more electrical tape on it now than the original insulation due to rodent chewage.

 

DTC P0138: Oxygen Sensor Circuit High Voltage
DTC P2195: Air/Fuel Ratio Sensor Stuck Lean

The basic problem is that the engine air/fuel ratio is on the lean side. I suggest that you check the engine oil filler cap and oil dipstick to ensure the cap is tight and the dipstick is fully inserted. Check the two PCV hoses to make sure that they are inserted into their fittings at the throttle body. (You probably can't see the other end of the hoses at the valve cover.) Check the connection between the air cleaner housing and the throttle body to make sure the screw clamp is tight.

If this is all good, then raise up the front of the car on jackstands, get under the car and check the wiring to both the air/fuel and oxygen sensors to see if there is any damage.

If you don't find any problems, then replace the air/fuel ratio sensor first and reset the DTC. Then drive the car and see if the DTC returns. If so, then replace the oxygen sensor, reset the DTC and drive the car.

If your car still logs the same DTC after doing all of this, then you may have a fuel line pressure problem or a fuel injector problem.

I recommend that you buy the correct Toyota air/fuel ratio sensor and oxygen sensor rather than buying aftermarket.

 

Bosch is a good aftermarket option.

 

I disagree. Bosch can make great stuff for the OEMs, but much of their aftermarket line is decidedly down-market. And if a dealer has to sort out the problem later, they may not want to mess with the non-OEM parts. If not, their first order of business will be to toss the Bosch sensor.

 

Yes.

Another reason I suggest buying the correct Toyota parts is that, in the event the OP is not successful in fixing the problem, when the dealer tech takes a look at the car and sees non-Toyota parts, they will be deemed suspect and the OP will have to pay undiscounted prices for the correct Toyota parts, plus the labor involved in installation.

If the OP buys the Toyota parts on his own then he has a chance to buy from one of the Toyota dealers that offer ~25% discount from MSRP for web orders.

 

Perhaps the OP should check the air filter and clean the MAF sensor before replacing parts. It's easy enough to clean, just get the CRC MAF cleaner and follow the directions.

 

Patrick and jk450, I respectfully disagree with both of you. If either of you have stories of Bosch O2 sensors being a disaster in the Prius compared to paying extra for the Toyota part, please start a new thread so as not to hijack this one. I've yet to have a problem, or hear of others who have had a problem, with Bosch O2 sensors. I'm not claiming that all Bosch aftermarket parts are good, but they did invent the O2 sensor. From experience on the Honda Insight side, a 5 wire Bosch A/F sensor, $175 from Amazon, is the replacement of choice, given that the Honda MSRP is $400.

Edit: I started a new thread on aftermarket parts. Please continue this part of the discussion there.

 

I won't argue the question about whether the aftermarket Bosch O2 sensor is actually better or worse than the Toyota-supplied part.

My main point is that if the OP cannot repair the problem himself and has to go back to the dealer for help, the first thing the dealer tech will do is to replace, at the OP's expense, any non-Toyota parts that are potentially relevant to the car's problem. Hence, the OP will now be paying for these parts 2x, at highly disadvantageous prices.

The correct Toyota air/fuel ratio sensor costs $162 while the oxygen sensor costs $113 here:
Champion ToyotaWorld

I do not think these prices are so high, as to make it worthwhile to use aftermarket which may have the wrong wiring harness connector, etc.