NaVeeD

Hello everyone..i bought GS300 2003 around 5months back. I live in Dubai and it was shipped from California. When i bought the car i changed spark plugs and coils. Recently i am starting to get Check engine , VSC and VSC OFF. I check the codes and i also get a PO430 pending code on OBD! I dont know what to do or where to start from i changed the O2 oxygen sensors but no luck i am also having an issue with petrol as it takes too much can anyone help thank you

slaapen

Have you cleared the codes and see if they came back after you changed the sensors?

NaVeeD

Thank you for replying,
yes i cleared the codes and it comes back on
yes i have changed the sensors twice in 3days but no luck

slaapen

So you've changed all the o2 sensors and still came back on which means there's something before the o2 sensors that's triggering them.

If you don't pump premium gas, then that should be your first start. Have you tried checking or changing the MAF?

NaVeeD

i am pumping premium gas only octine 98 .. i cleaned the maf sensor 3months back but i think its fine..i toke it to the workshop and the guy said i need to change or clean the converter!! 🤦🏻*♂️ thats cause im getting a Po430 code

slaapen

Before you take the cats out and replace them or clean them, are your o2 plugs grounded good and not corroded? A low circuit reading might indicate it's not get a full 12 volt reading on the o2 sensor?

bruceb58

Look at his first post and look at what was setting the code for the O2 sensor. It's the heater circuit that is failing, not the O2 output. BTW, O2 sensors do not put out a 12V output...much lower voltage.

Premium fuel has nothing to do with anything. The Octane of the fuel has no effect on O2 performance.

To the OP, your cat code can get set if you have an exahaust leak upstream of the Cat convertor. Make sure you check that before replacing it. When you replaced the O2 sensor, did you use the antiseize that is designed to be used with O2 sensors? It has to be a conductive type of antiseize. Are you using OEM O2 sensors like Denso?

What do you mean it takes to much petrol? What type of mileage are you getting? Does the engine seem to be operating correctly? Are you low on power?

NaVeeD

yea i checked for any exhaut leaks but there isnt any leaks and yea i did put the original O2 sensors

i get a very bad mileage and when the car is stopped and when i push the gas the accelration is so bad

update:

i changed my converter as well but the issue is still there check engine, vsc and vsc off! Can anyone help me out or ill have to sell this car off. It has started to get on my nervous now but i love this car! Can anyone help?

vijayn

It could be a the main heater circuit that needs repairing as in the 12V source for all four heater coils. They should be coming from one main supply, maybe a relay / fuse. I would have a look at a wiring diagram and check where the 12V source is coming from for the heater coils for the o2 sensors and go from there.

bruceb58

It's the same 12V that comes from the fuel injection relay and it also is the source for the O2 sensor itself.

This, of course, is all in the wiring diagram service manual and can be easily checked with a meter.

vijayn

Yeah true, it looks like the 12V supply from the EFI Relay supplies quite a few components. According to the attached wiring diagram, check for 12V on the "Black/red wires on your oxygen sensors. This is the heater 12V supply. If you don't get 12V there while ignition is on, then work you way back to the two junction connectors "J/C 11" and "J/C 3" on the diagram.

The diagram is not put together in the proper order so you will have to scroll up and down to get match where the wires are going.

bruceb58

Not only is it the supply to the heater circuit but it is the supply for the O2 sensor itself. Could be a resistive circuit I guess and still allow the O2 function to work but I am thinking you would have bigger problems if there was a problem in that 12V supply circuit.

vijayn

These oxygen sensors on our GS300 are not the wideband type or the Titania type, they are the narrow band Zirconia type. When heated up, they will produce there own voltage depending how much o2 is coming into the exhaust. They don't have or need a supply to run them unlike the Titania type.
The reason I say to check the heater circuit connection is because the code isn't a "lean" code. The only way for the those heater circuits codes to come by is open circuit on the heater supply or ground or all 4 o2 heater elements are actually faulty

bruceb58

OK..agree with you. Definitely worth checking out the heater voltage.

NaVeeD

thank you everyone for commenting but i dont have the meter nor i know how to check the wirings ill take it to the wiring shop and tell him to check all the wirings

just wondering if anyone is in Dubai who can suggest me a shop? Thank you