O2 Sensor

[BlueNSX]

The TCS and Engine Light are illuminated On Dash :no: I was told that this = O2 Sensor failure.

Will decats cause this ?

How do you tell if its the front or back sensor ?

Does Dali have the best replacement ?

Any suggestions please

Many Thanks

[goldnsx]

Mark,

I hope you got home well after the Le Mans weekend. It's was great fun!

Who told you that it's a o2-sensor? Did you pull the error codes to confirm?

[markc]

I think it was me, Mark and I met earlier today.

"Check Engine" and "TCS" lights illuminated on the dash just means there is some sort of problem. You need to pull the OBD Code to understand what the cause is.

I have the "Check Engine" and "TCS" lights illuminated on the dash. I pulled the codes using the paper clip method, 4-2 in my case, which is "Rear Primary HO2S Heater Circuit Malfunction (Bank 1 Sensor 1)".

Passed the MOT last week like it anyway :)

Mark

[AR]

I had the same problem before. As others have said the most likely cause is a failed 02 sensor. Since you had headers recently it could be that they used some sort of penetrating oil and buggered them. Or maybe Honda did it by spraying the same on the Cats. BTW before you go throwing money at it, check the wires they used to extend them as there might be a loose connection somewhere.

When this happened to me the car would not go into VTEC at times.

Cheers,

Ary

[Silver Surfer]

Remove and plug back in the clock fuse and see if this removes the error code.

The same happen to me when I decatted the car and fitted bypass pipes. I hade also replaced one of the O2 sensors (or Kevin of Kevspeed did :D).
The light disappears after you switch of ignition and switch on again and gradually it appears less and less.....fingers cross it has not happened for the last 1000 mile run. It seems to come on only when accelerating in the higher gears (4-5th)! It seems to keep away when the error code has been reset.

SS

[goldnsx]

I think it was me, Mark and I met earlier today.

Oops, sorry for the confusion.


"Rear Primary HO2S Heater Circuit Malfunction (Bank 1 Sensor 1)".

Interesting error code I've heard of two times. In one case they've changed the o2 sensors and checked wires according to the manual. Still had the error code. They finally changed the ECU but the car is not finished yet. I hope for you that it's the o2 sensor but believe that in many of those cases it's the ECU itself. *fingers crossed*

The behaviour Silver Surfer describes is also know on Prime on OBDII cars. They just reset the ECU from time to time.

[markc]

Interesting error code I've heard of two times. In one case they've changed the o2 sensors and checked wires according to the manual. Still had the error code. They finally changed the ECU but the car is not finished yet. I hope for you that it's the o2 sensor but believe that in many of those cases it's the ECU itself. *fingers crossed*


This should be a very straightforward one for the car (it's ECU) to diagnose. It's looking at the O2 sensors heater circuit and if it finds it completely open circuit (wire broken) or closed circuit (shorted out) it throws a fault. In the case of an OBDII NSX (with 4x O2 sensors) it'll be either...
Front Primary HO2S Heater Circuit Malfunction (Bank 2 Sensor 1)
Rear Primary HO2S Heater Circuit Malfunction (Bank 1 Sensor 1)
Front Secondary HO2S Heater Circuit Malfunction (Bank 2 Sensor 2)
Rear Secondary HO2S Heater Circuit Malfunction (Bank 1 Sensor 2)

Here's my understanding of the basics of O2 sensors and how the car uses them...

The O2 sensor/s are there to measure air/fuel ratio (mixture) via the exhaust gas. If the mixture is too rich (too much fuel) the ECU instructs the Fuel injection system to inject a bit less fuel, if it's too lean (not enough fuel) it instructs the Fuel injection system to inject a bit more fuel. This is called closed loop operation.

O2 sensors, by the nature of the materials used in them, need to be hot to work. Each one therefore has it own heater element which helps bring them up to operating temperature. This still takes a little time though (30-60 secs) so during this period the ECU doesn't bother using the signal from them. The ECU uses a fixed air/fuel ratio and does not go into closed loop operation.

At start-up the ECU tests the O2 sensors heater circuits and if it finds a short or open circuit it thows a fault and illuminates the Check Engine and TCS lights on the dash. Interrogate the system (with a paper clip :) ) to determine the cause of the fault.

It could in theory be the ECU finding a fault with itself ie the section that reads the heater supply, but it is much much more likely to be the O2 sensor (heater element) itself or a damaged wire supplying it.

In an OBDII car, O2 senors are placed either side of the CAT/s. The ECU is looking for a higher O2 reading (voltage) after the CAT/s to determine that the CAT/s is working. If you remove the CAT/s you have to "frig" the second O2 sensor to read higher than the first. The most reliable way to do this would be electronically ie intercept the signal voltage and modify it to be the correct level. The other way is to move the O2 sensor further out of the exhaust gas flow so that it reads differantly. The latter is what most de-cat/bypass pipes do but you may well get errors.

It depends on what the ECU actually does with these readings, ie use them to alter the air/fuel mixure, as to whether you'll experience any performance issues or if you just have to pull the clock fuse every time it does.

Cheers

Mark