Downstream O2 sensor complications in Suzuki K12M

Hi,

If i go for an aftermarket exhaust system for my Suzuki Swift VVT which has a downstream O2 sensor what complications am i looking at by the absence of a catcon before the sensor.

Will an O2 sensor spacer or isolator correct this issue as it will take the sensor out of the exhaust stream. If this doesn't solve the issue then how do i solve the CEl problem and optimum performance of the engine?

If you have 2 lambda/O2 sensors/probes (or whatever people want to call it) one of them being pre cat and the other one being post cat then you should do the following:

First sensor should be in the down pipe after the header. Because of the pulsing and the back draft it can otherwise come to reading problems affecting performance and fuel consumption.

The post lambda probe is best put in a sealed sleeve/isolator, but needs to be connected to the ECU.

If the engine management warning light comes on then performance will be affected as most ECUs go into safe made. When rectifying the problem it might take several times starting the engine and driving the car before the warning light comes off.

I never have come across myself the problem that even with the probe in the isolator the warning light would come on, but heard that some people hat the problem. This could be that they have swapped pre lambda with post lambda, which sends the ECU into safe mode.

Ok, i hope i understood you right. For best performance the first O2 probe should be in the collector. and second can be anywhere after the first(?) but should be in a isolator.

Lengthening of the probe wires are required then, the OE location of the first probe is close to the head.

Another question, are the first and second probes identical in their construction apart from the lengthier wires of the second one?

Thanks for replying Peter.

The post lambda you leave out of the exhaust pipe and just stick it into the isolator. Just plug it into the elctric socket.

You can use the post sensor as the first sensor because of the longer wire. Sometimes you have a little plastic nose on the connector preventing plugging it so that the sensors can't be swapped accidentally. Often this nose can be cut away and you can fit the sensor. So try this first instead of trying to lengthen the cable.

I disconnected the down stream O2 sensor coupler this evening and went for a short 2km drive, the CEL didn't come on. I was expecting to see the CEL light as soon as i started the car. But it never came on not even after the drive. Why?

crankysan wrote:

I disconnected the down stream O2 sensor coupler this evening and went for a short 2km drive, the CEL didn't come on. I was expecting to see the CEL light as soon as i started the car. But it never came on not even after the drive. Why?

It depends on the software. Some ECUs do not react because the lambda might not be heated. In other cases the ECU software is not adapted to use the post lambda.

In other cases it might take a bit of time to come on.

The post lambda is not as important as the pre cat lambda. It still might log it on as a fault, but nothing will show on the dash.

Nano fan wrote:

In other cases it might take a bit of time to come on.

The post lambda is not as important as the pre cat lambda. It still might log it on as a fault, but nothing will show on the dash.

I'll update the thread this evening after a longer test drive. I hope no CEL comes!
I'll connect the BT OBD scanner and see any error log exists reg the 2nd sensor.

crankysan wrote:

Nano fan wrote:

In other cases it might take a bit of time to come on.

The post lambda is not as important as the pre cat lambda. It still might log it on as a fault, but nothing will show on the dash.

I'll update the thread this evening after a longer test drive. I hope no CEL comes!
I'll connect the BT OBD scanner and see any error log exists reg the 2nd sensor.

Be aware that some manufacturer's specific codes might not be picked up with the scanner, which is due to infringement reasons.

Went for a longish 50km test drive and no CEL popped up yippeee

But when i plugged in my BT OBD scanner the CEL popped up in the meter console and i searched for error log with the Android app. The error shown was sensor 2, bank 1 heating circuit incomplete... it didn't say the sensor was faulty or the cat was faulty, it just said heating circuit incomplete. I cleared the error and the light disappeared. There wasn't any power loss with the light on.

So there goes the reason why lots of people on various forums reported no CEL with 2nd probe decoupled. The light comes on the moment the scanner is plugged in. Makes sense since the second sensor isn't critical so the CEL isn't lit during regular usage, but when a scanner is connected to the port the ecu lights up the CEL so that the technician can look into it.

I am glad to hear it. I wish it would work the same way on our Marelli and Bosch ECUs.