Oxygen sensor general info

Just thought I'd summarize O2 information for people as these cars get older.




(Gen 2 Repair Manual states: Drive the vehicle at 44 to 70 mph for 5 to 10 minutes.)


Oxygen Sensor OX1A (Gen 1 only)
Bank 1 Sensor 1
Upstream (on exhaust manifold)
Wideband O2 sensor, Engine ECU uses this to adjust fuel trim (replaced with A/F in Gen 2)
Voltage varies rapidly from 0.1 to 0.9V (average around 0.5V approx 2Hz) when ICE is running
Check with voltmeter pin 12 connector E10 (gen 1)
Generic OBD2 reader as O2V11
http://priuschat.com/forums/gen-ii-...ation-oxygen-sensor-bank-2-a.html#post1372802


Oxygen Sensor OX1B
Bank 1 Sensor 2
Downstream (on exhaust after cat)
Narrow band O2, ECU uses this to determine Catalytic efficiency or problems
Voltage changes very slowly hovers around "0.6V to 0.7V" (0.8? or 0.9? normal?)
Check with voltmeter pin 11 connector E10 (gen 1)
Generic OBD2 reader as O2V12
Prius 1st gen - Replacing the Catalytic Converters
The down stream O2 sensor can be accessed by removing the floorboards in the passenger compartment.

You can directly measure the resistance of the heater element on the 4-pin oxygen sensor plug. Measure between pins 1 & 2 and it should be 11 to 16 Ω at 20C. (Assuming same heater for the upstream O2 sensor)


Possible DTCs
P0135 - Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 1) or
P0141 - Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 2)
* Heater current is less than 0.25A (at 0.3 second after heater is turned ON)
* When the heater operates, heater current exceeds 2A
P0130 - Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 1) (Except Calif.) or
P0133 - Oxygen Sensor Circuit Slow Response (Bank 1 Sensor 1)
* Output voltage does not both go above 0.48V and below 0.42V (bad if always too low, always too high or always between 0.42 and 0.48)
P0136 - Oxygen Sensor Circuit Malfunction (Bank 1 Sensor 2)
* Output voltage remains between 0.45V and 0.55V when driven over 62 mph

HCAC Bypass Valve (Gen 1 only)
P1436 - Bypass Valve Malfunction
* Bypass valve not operating during cold start or warm coolant but engine load > 30%
P0420 - Catalyst System Efficiency
* deteriorated response for Sensor 1 Bank 2 (downstream)

If you have DTC codes related to downstream O2 or the catalytic converter for a Gen 1 Prius, please check this:


Stupid, criminally designed, exhaust diverter. This would be the view looking down from the armrest if the floor was transparent. You need to work the linkage rod free and make sure the vacuum hose that connects on the lower left of this picture (into the diaphragm) is working to move the linkage. You can put a brake vacuum pump on the diaphragm to operate it. It is part of the $1700 one-piece catalytic exhaust so be careful and keep that thing free and maybe use high temp grease.

Scavenges exhaust during cold start and during deceleration:



Other
Upstream catalyst = between 430C and 800C (vary with vehicle speed)
Downstream catalyst = between 290C and 675C (vary with vehicle speed)

Other relevant threads:
http://priuschat.com/forums/generation-1-prius-discussion/96134-oxygen-sensor.html
http://priuschat.com/forums/generation-1-prius-discussion/92240-oxygen-sensor-replacement.html
http://priuschat.com/forums/gen-ii-prius-care-maintenance-troubleshooting/103565-cel-code-p0138.html
http://priuschat.com/forums/gen-ii-...on/96929-location-oxygen-sensor-bank-2-a.html
http://priuschat.com/forums/gen-ii-...ooting/89967-oxygen-sensor-collar-around.html

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Gen 2
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Gen 2 - Removed bypass valve


Gen 2 - added DTCs for Bank 1 Sensor 2 (downstream)
P0136 - Malfunction
* Heated oxygen sensor impedance Less than 5 Ω
* Output voltage (max) less than 0.6 V or (min) always above 0.24 V
* 30 seconds or more, Estimated sensor temperature Less than 750C (1382 F)
P0137 - Low Voltage
* Heated oxygen sensor impedance 15 kΩ or more
* Output voltage always less than 0.25 V
* 55 seconds or more, Estimated sensor temperature 450C (842 F) or more, Intake air amount More than 0 g/sec
P0138 - High Voltage
* Output voltage always over 0.6 V
* 1.2 V for 10 seconds or more.


Gen 2 - New A/F Bank 1 Sensor 1 (upstream)
In Gen 2, Bank 1 Sensor 1 sensor replaced with planar A/F wideband sensor
A/F sensor (upstream) info from Patrick Wong http://priuschat.com/forums/toyota-...10-o2-air-fuel-ratio-sensors.html#post1311984
Toyota 2004 Prius wiring diagram shows the following color coding (bank 1 sensor 1):
Red: AF+ (sensor connection to Engine ECU)
Green: AF- (sensor connection to Engine ECU)
Yellow: Pulse width modulation for A/F heater
Black: +12V
* The heater current is supposed to be > 0.8A and < 10A or else a DTC will be logged.
* A/F sensor heater element resistance (pin 1 and 2) should be between 1.8 to 3.4 ohms (at 20C [68F]).
* A/F sensor has warmed up, at idle speed the sensor voltage is supposed to fluctuate from < 3V to > 3.35V.
* If the voltage remains greater at all times, then the air/fuel mixture is lean.

Sensor voltages on ECM on Connector E5 pins 23 to 28 and Connector E5 pins 22 to 28

A/F sensor (upstream)
Less than 3.0 V == +25 % injection volume (rich)
More than 3.35 V == –12.5 % injection volume (lean)

Oxygen sensor (downstream)
More than 0.55 V == +25 % injection volume (rich)
Less than 0.4 V == –12.5 % injection volume (lean)

.

 

I would be curious anyone with scanguage or even generic OBD-II what the historical reading is on the downstream O2. I seem to get over 0.8V and it will stay that way even a few minutes after the ICE is off. I would think it would want to be around 0.5 if engine, but I have a +3% LTFT. Anyways, it would be good for a benchmark of known good versus aged or going bad ones.

 

I edited the post to include the Manual test condition of 55mph for 5 mins, Bank 2 (downstream) should be 0.6V to 0.7V.

 

I would really like to get some more feedback from others on the downstream O2 sensor. From digging into all these details, it is clear to me that Toyota added DTCs for this sensor that are not in Gen 1, but the sensor is the same one.

It is my belief that you can have a bad downstream sensor that will lead to the ICE running rich if the voltage stays too high and doesn't change voltage. From what I can tell you can run with downstream O2 always at 0.9V in Gen 1 and no codes will be thrown, but you will probably be throwing way too much gas down the cat. Leading to poor mileage and needing a new cat after a short time.

It could be the downstream O2 sensor is only used to throw trouble codes just to confirm the catalytic converter is working. The manual implies the Engine ECU also uses downstream voltage to adjust the Fuel Trim. Does anyone know? From what I gather, any downstream reading above 0.5V means there is less oxygen which means the cat is doing it's job, assuming it isn't high because of extra unburnt fuel. The voltage should also change more slowly downstream because extra fuel is absorbed by the cat when it is rich and then the injectors go back to lean it absorbed some extra fuel to catalyze when lean, which smooths out signal. If downstream varies a lot that means you are bypassing the cat or it isn't absorbing and/or catalyzing.

 

Can this be a sticky?