Follow me here. It is my understanding that the 98 Cobra has three O2 sensors: one at the cylinder head and two in the ehxaust flow prior to the catalytic converter.
I have recently been experiencing my check engine light on. I took the car to Auto Zone where the woman () read my codes and told me they indicated a faulty #2 O2 sensor which could mean a few different things.
SO, #1 sensor is okay telling me theO2 intakeis on track. But the code indicates the #2 so I am wondering how,. if at all I can be surethe #2 sensor is bad and not just reading rich because I added a bottle of Valvoline SynPower fuel system cleaner to my tank before filling and now the injectors are working too well, adding too much fuel for the computer tune settings adjusted with clogged injectors? I guess I could (and will) test it electrically. But in the mean time I would like my check engine light off so, how do I do this without ruining anything computer related? And since i am experiencing no engine toruble can I assume since the code indicates the #2 sensor that the O2 intake is still functioning properly?

Thanks, Ian

 

What were the codes? Autozone's interpretation (woman or not) is worth a bit, the actual codes read are worth alot more...

 

I know the codes were interpreted to tell there was a malfunctioning HO2S 22 circuit.

 

98 Cobra has 4 O2 sensors total just to let you know. Two at each manifold and two after the catalyic converters.

 

yes, you are right. Thanks for the information.

 

Next question. Can a mixture be too rich and have the exhaust O2 sensor register above it's high end range?

 

[/align][/align]No, in fact a very rich mixture (> 9.5:1) will make a PZ O2 sensor output go low.[/align][/align](more than you probably want to know about PZ O2 sensors)[/align][/align]There are a number of O2 sesnor codes, some of which indicate a malfunctioning sensor and some which indicate a functioning sensor indicating that something else is wrong--it is important to know exacty which code was read to diagnose the problem remotely...[/align]

 

Thanks for the help thus far Cliff. The code was PO156.

My manual recommended I back probe the sensors with the car warm to get the voltage output for each sensor. I got a bit comfused about what back probing was and so I think I may have tried to read the voltage incorrectly. Will I be reading from the sensor side of the connectoror the wiring side?

 

P0156 indicates a malfunctiong rear, driver's side,sensor--which shares troubleshooting info with P0136. Possible causes are:[/align][/align]
Pinched, shorted, and corroded wiring and pins.
Crossed sensor wires.
Exhaust leaks.
Contaminated or damaged sensor[/align][/align]When measuring O2 sensor voltages you need to keep the connectorconnected, and pierce (or cut-back) the insulation on the wires. The sensor must be hot or heated to operate correctly, and rear sensors must be heated as the exhaust gasses are too cool at idle to keep it hot (at least 662°F). If you unplug the connector the heater will obviously not be working.[/align][/align]The sensor generates a voltage, so if you could test the voltage with it disconnected (and you could maybe if you could unplug and test fast enough) you would be testing the sensor side of the connector.[/align][/align]You could also remove the sensor and perform the bench test shown on my O2 sensor page.[/align]

 

Here's the latest... I disconnected the sensor and re-connected it, drove the car for about 15 miles and the CEL went off. Problem solved. I think my gas system cleaner contaminated the sensor a little, or maybe the rich mixture left some high levels of fuel and got a bit confused...