Emission Warning Light

Bryn I have a couple of readers I can pop by after work if you want?

Lambert
Many thanks I’ve sent you a PM.

My neighbour has a reader and so it’s come up with “P0420 catalyst system below threshold” which guessing is something to do with the lambada sensor. Suggestions please
Bryn

As I said. Cold and wet where you are? Any mods like mine?

If it is emissions, then it is triggered by the post- catalyst sensor.

There are two sensors:

One in the exhaust before the catalyst (pre-cat sensor) that is used for fuelling. If it fails the fuel consumption usually goes up as the car defaults to a basic fuelling map.

One after the catalyst (post-cat sensor) this checks the catalyst is working by looking for a reduction in oxygen content compared to the pre-cat sensor. (It reduces because the catalyst reacts any nasties with oxygen)

If the oxygen doesn't go down, the emissions warning is triggered (catalyst system below threshold), but the car drives just fine, no limp mode, no increase in fuel consumption.

This may be because

1) the catalyst is worn out/poisoned and it cannot do its job (new catalyst required)
2) The catalyst isn't reaching operating temperature as yakuza says- maybe you are driving trough a lot of water which is cooling it down.
3) there is a leak in the exhaust somewhere before the post-cat sensor, and air is being drawn in, which provides the extra oxygen.
4) the sensor is out of calibration (new sensor required)

I'd have a look for a leak in the exhaust where the pipe goes into the catalyst.




 

bryn wrote:

Unfortunately that obd code reader recommended by Pheaton isn’t compatible with my iPhone. Can anyone recommend one please
Bryn
And just for clarity it’s the yellow engine management light which I have assumed is the emissions light. Thanks

Apologies for that, as it's Bluetooth I just assumed it was suitable for both flavours as I know Torque is compatible

bryn wrote:

My neighbour has a reader and so it’s come up with “P0420 catalyst system below threshold” which guessing is something to do with the lambada sensor. Suggestions please
Bryn

First, be aware that on newer (anything built after 2003) vehicles there are two lambda sensors, one before the catalytic converter and one after.

The first sensor, known as the upstream sensor or B1S1 (Bank 1 Sensor 1 on an inline engine) is used to determine the fuel mixture, the second  sensor, the down stream sensor or B1S2 (Bank 1 Sensor 2) is used to ensure the catalytic system is working properly - the output of B1S1 would normally be a constantly changing voltage between roughly 0.1~0.9 VDC, the output of B1S2 would normally be a relatively stable voltage around 0.5~0.7 VDC - a P0420 code is set when the output of B1S2 closely matches the output of the B1S1 sensor

You need to look at the waveforms being output from the sensors, an exhaust leak upstream the B1S1 sensor can cause that sensor to "level out" so the output is similar to that of the B1S2 sensor, or a defective cat converter can cause the B1S2 to vary in the same manner as the B1S1 sensor.