Error Code

[Zxrob]

Guys and Girls

I put a decat exhaust on the MR2 last year, wired in a resistor to "fool" the ecu, all has been fine, probably done around 6-700 miles with no issues, today, went for a long drive and the engine light came on, got back, plugged in an OBD and error code P0420 came up which is to do with the cat,tried to erase the code but could not, now, two things

1. why would it come on after such a long time, I have checked the wires and all where I soldered is fine

2. Why wont it let me erase the code, the reader is a cheap bay one, memoscan U480,

Cheers Rob

[Ardent]

1. In normal situations the light comes on after two trip logic.
Given the resistor mod that may change things.

2. May say more about the reader than the 2. I would have expected it to have cleared the code.

[Zxrob]

1. In normal situations the light comes on after two trip logic.
Given the resistor mod that may change things.

2. May say more about the reader than the 2. I would have expected it to have cleared the code.

Thanks for the reply

2. I thought it may be the reader, I also googled it and found a couple of instances where a cheap reader would not erase the code, I suppose I could check it, if I say removed one of the precat sensor plugs, I presume that would throw up a code I could try and remove

1. I wander if the resister has over heated and gone caput as it is quite close to the exhaust

Cheers Rob

[Ardent]

I like 2. Easy test.

May or May not need to be up to temp. Ecu only takes input when warm. That said I would to think it would throw a code straight off. In a, hey wheres the sensor gone  kinda way.

[Ardent]

Anyone local with a second reader?

[Petrus]

Disconnect the battery for 15 minutes or so.
Should clear the memory.

As to the sensor; I mounted in a distance piece. Simpler and reliable.

[Gaz mr-s]

I'm puzzled by resistor being used in connection with a de-cat pipe.
I have a de-cat pipe on mine, & it has the boss for an O2 sensor.

The job involving using a resistor I know of is if the beater circuit goes in an O2.

So what's this one?

[thetyrant]

Where did you wire in resistor ?   Usually you wire them into the heater wires circuit on lambda sensor when it starts acting up (different code to this), its nothing to do with signal sensor gives to ecu about what is going on in the exhaust so weird if you didnt get PO420 cat code until now.

As above if fitting decat (or sports cat sometimes) you need an extender/defouler on Lambda sensor post cat to trick ecu into thinking there is a good working cat in system, it works by moving the sensor further away from its normal position  right in exh stream and has smaller hole so less exh gas gets to it, which is usually enough to trick ecu and keep light off.

[Petrus]

I'm puzzled by resistor being used in connection with a de-cat pipe.
I have a de-cat pipe on mine, & it has the boss for an O2 sensor.

The job involving using a resistor I know of is if the beater circuit goes in an O2.

So what's this one?

When you fit the sensor t the decat pipe without any provison, the ecu will through an error code because it registers the cat is not funtioning.
To avoid this, the sensor needs to give the correct signal as if the cat is fitted.
This can be doen by a distance piece, taking the sensor out of the direct flow or electrically but putting a resistor in the wire, lowering the voltage of the signal to the ecu.

[Zxrob]

I'm puzzled by resistor being used in connection with a de-cat pipe.
I have a de-cat pipe on mine, & it has the boss for an O2 sensor.

The job involving using a resistor I know of is if the beater circuit goes in an O2.

So what's this one?

I think I got carried away, I wired in the resistor to eliminate the 02 codes, which it has done, you are correct, what would cause the P0420 code to come on, how does it sense/where would the ecu get that reading from

Cheers Rob

[Zxrob]

Where did you wire in resistor ?   Usually you wire them into the heater wires circuit on lambda sensor when it starts acting up (different code to this), its nothing to do with signal sensor gives to ecu about what is going on in the exhaust so weird if you didnt get PO420 cat code until now.

As above if fitting decat (or sports cat sometimes) you need an extender/defouler on Lambda sensor post cat to trick ecu into thinking there is a good working cat in system, it works by moving the sensor further away from its normal position  right in exh stream and has smaller hole so less exh gas gets to it, which is usually enough to trick ecu and keep light off.

Ha, you posted this as I was typing
Yes wired into the heater plug to eliminate the 02 codes which it has done, yes there is a boss welded onto the pipe for the sensor that comes up the back of the headlight, do I just fit the extender in that, will that eliminate the P0420 code

Cheers Rob

[Petrus]

do I just fit the extender in that, will that eliminate the P0420 code

Cheers Rob

Eliminate no, prevent it coming up again yes.
You need to clear the memory for the code to get erased or reset it through the OBD port.

[Gaz mr-s]

Ha, you posted this as I was typing
Yes wired into the heater plug to eliminate the 02 codes which it has done, yes there is a boss welded onto the pipe for the sensor that comes up the back of the headlight, do I just fit the extender in that, will that eliminate the P0420 code

Cheers Rob

I wired in a resistor to stop a P0135 heater cct code last year, but read later that if an O2 sensor fails like that it's probably past it's best & the emissions aspect may not be working as well.
An extender may solve your emissions code, if not may need a new O2. I'd recommend a brass one.

Since you did soldering you'll do crimping too.  Just look for the cheapest Denso 4 wire sensor you can find, get a cheap crimping kit, & use the Toyota-fit plug from your faulty sensor. One solution is a Dox-0109