Multiple Error Codes - P0138, U0293, U0100

If you're really serious about becoming more proficient in diagnosing electrical/electronic issues, then you need to purchase a mid-tier multimeter (if you do not have one already) then you need to learn to use it by finding some good tutorials on YouTube that can teach you the basics of multimeter use and follow that up with some on basic automotive diagnostics.

Search this forum for Prius Repair Manual or Prius Electrical Wiring Diagram to download as you will need that information to guide you in diagnosing any codes you might pull from any of your car's ECU.

The P0138 indicates a problem with the electrical circuit of the upstream oxygen sensor. It is seeing voltage higher than it should be. The wiring damage may have in turn damaged the sensor or the sensor heater.

The U0100 indicates a communication problem between the power control module and the engine control module.

So, it seems likely you could have wiring damage in wiring that is common to both areas. Or, two unrelated wiring issues.

 

P0138 code description is Bank 1 sensor 2 (downstream) oxygen sensor circuit - "high". The signal from that O2 sensor varies from near 0.0V (lean condition) to near 1.0V (rich condition). If the signal is "out of range" high, or if it is higher than the ECM expects - then it can set this code.

You really want to look at engine data with a decent scantool. With a warmed up engine, normally A/F sensor reads around 3.3V, short and long term fuel trims are "near" 0% (+/- 5%), and O2 reads "around" 0.7V with a good catalytic converter.

One possible fault, the A/F is bad and "lies" (a little)- fuel trims go to maybe +10%, and O2 reads 0.8 to 0.95V. Still in normal range but sets a P0138- and the problem is the A/F sensor.

Or something in the O2 sensor is bleeding voltage from the heater circuit into the signal. Scantool shows about 1.25V (the max it can display) and sets P0138- this time it is the O2 sensor.

Or maybe there's corrosion or damage to wiring somewhere. Almost anything is possible.

But a blown fuse ain't really on the list for this.

A fuse problem can cause a U-series comm code, but if it was a fuse, then the car wouldn't run if one of the "major" ecu's (ECM, hybrid control, power mode, etc) couldn't communicate at all.

Also, the code listing on your post make me think that you're using a scantool like CarScanner, that only talks on the CAN network. Many systems on a Gen2 Prius don't talk to a scantool via CAN. You might have additional codes in other systems that can help in diagnosis.

I prefer a scantool that reports what systems it can communicate with and which ones have what codes.

You might want to read this thread that reviews several scantool apps and OBD2 devices. Some can scan all 15-16 systems on a Gen2.

https://priuschat.com/index.php?posts/3290690

Posted via the PriusChat mobile app.