P0420 code wide wideband oxygen sensor on B1 S1 narrowband o2 sensor on B1 S2

the description of the fault code P0420 is catalytic converter ageing loss of effectiveness
long term fuel trim -0.781% STFT -0.781
B1 S1 -0.047mA
B1 S2 0.470 V
Sensor 1 not switching neither is sensor 2 fuel trims remain the same.
I am not sure weather S1 is at fault or the cat or may be both


see screen shots attached

david landman wrote: the description of the fault code P0420 is catalytic converter ageing loss of effectiveness
long term fuel trim -0.781% STFT -0.781
B1 S1 -0.047mA
B1 S2 0.470 V
Sensor 1 not switching neither is sensor 2 fuel trims remain the same.
I am not sure weather S1 is at fault or the cat or may be both

File Attachment:

File Name: 24718de000...18c1.zip
File Size:755 KB

File Attachment:

File Name: 24718de000...18c1.zip
File Size:755 KB

see screen shots attached

Peugeot 207 1.6 litre 2007

Sensor 2 is there to monitor the cat and is what the computer looks at to trigger this code.

B1s2 looks correct.

I would pull a vacuum hose and see how it responds to a vacuum leak. Force it rich and lean to see how the sensor responds if it responds at all. If it doesn’t respond do a resistance check on the heater circuits and do a wiring integrity check using a test light at the harness to make sure it responds.

Air Fuel sensors (wide band) work differently than narrow band. AF is a steady signal with changes measured in miliamps.

Check 3 PID's on your scantool for your 02.

voltage
mA
Equivalency Ratio

The equivalency ration will show if the engine is in stoch... 14:7.1 the 1 is the indicator to look at. 1 is stoch... greater than 1 is lean and less then 1 is rich.

Voltage is different for each manufacturer but typically 2 to 4 volts. This voltage should be fixed unlike the narrow band 02 which oscillates.

the readings indicate the engine is running rich due to a lean condition. the rear 02 if fixed at 450mv indicates that it might be bad. The rear 02 will influence the front 02 to maintain a healthy CAT. The P0420 does not necessarily mean the CAT is bad. Do more testing on the 02's. Make sure the heater circuits are working. The 02's have to be in closed loop to get correct readings. Induce propane and a vacuum leak to see if 02 respond.

You did not post what make model and year car you're working on...

Great advice so far. For what it's worth, I think this shot tells a lot of the story:



I can't say for certain, but I'm guessing that you were holding the engine speed off idle before frame 1.670? The two sensors are definitely moving in step with each other. The fact that the downstream sensor goes full range after you let off the throttle suggests the wiring and sensor are OK, IMO.

As a matter of good practice, it'd be a good idea to verify that fuel trims are within 10% of zero, no exhaust leaks and such. But at the end of it all, I think it's gonna need a cat.

As the above the sensors and fueling look okay

---

I think you are going to be buying a cat.
Wideband sensors are a different ball game from the narrow band Zirconia. Fuel control is much tighter and is proportional rather than bang-bang rich to lean "switching". The snap throttle test is the simplest, if the output from the wide band sensor goes rich instantly and recovers quickly and smoothly when the pedal is released and fuel trims are in an acceptable range the sensor is generall okay. You can force the mixture rich and lean with added propane as fuel then vacuum leak for an artificial lean condition but when the downstream mirrors the upstream so closely on a snap throttle it points to a bad cat rather than a biased sensor or other issue.

How much history do you have on the vehicle ? As looking again at the traces it makes me suspect the the cat is completely gutted.

the vehicle is a Peugeot 207 1.6 litre 4 cylinder. 2007 year

owner of the vehicle says its been like that for a while, it also has a lack of power