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[dandor]

Hi guys, Ive a problem with my omega, a few weeks ago my eml light came on, however the car still drove perfectly. I took the car to my local garage to be put on the diagnostic. The fault came back as the pre-cat 02 sensor, but when he checked it on the oscilloscope it was performing fine i.e the output signal was quickly going from 0.1 to 0.9 mv. The faults were erased and the car seemed fine for several weeks until the light came on again this time it was followed by terrible cold starting and a random occasional misfire which seemed worse at tickover. presuming it was the pre-cat again i changed it for a new one and had the faults re-checked on the diagnostics. Although i cant remember the exact codes numbers they were 1) Pre-cat 02 sensor 2) post-cat 02 sensor 3) immobiliser fault 4) heater circuit open 5) engine lean. Also when we looked at the readings from the pre and post cat 02 sensor the output from the precat was just a flat line of 0.1mv. Is there something simple im missing that could be linking these faults together and making a brand new 02 sensor give a bad output? my car is a 2.2 petrol 2001 cd auto. engine is z22xe. many thanks in advance. Dan

[zirk]

Hi guys, Ive a problem with my omega, a few weeks ago my eml light came on, however the car still drove perfectly. I took the car to my local garage to be put on the diagnostic. The fault came back as the pre-cat 02 sensor, but when he checked it on the oscilloscope it was performing fine i.e the output signal was quickly going from 0.1 to 0.9 mv. The faults were erased and the car seemed fine for several weeks until the light came on again this time it was followed by terrible cold starting and a random occasional misfire which seemed worse at tickover. presuming it was the pre-cat again i changed it for a new one and had the faults re-checked on the diagnostics. Although i cant remember the exact codes numbers they were 1) Pre-cat 02 sensor 2) post-cat 02 sensor 3) immobiliser fault 4) heater circuit open 5) engine lean. Also when we looked at the readings from the pre and post cat 02 sensor the output from the precat was just a flat line of 0.1mv. Is there something simple im missing that could be linking these faults together and making a brand new 02 sensor give a bad output? my car is a 2.2 petrol 2001 cd auto. engine is z22xe. many thanks in advance. Dan

heater circuit open 5, could be the Key, check connections for the Heater, or measure the resistance, should be low Ohms not High Impedance, check the Cables to the O2 Sensors haven't been cooked.

[dandor]

Hi Thankyou for your quick reply. ive just been out and checked the connectors for that part of the loom and all seems fine. i cant find no splits or corroded wires. what does heater circuit open actually mean? is it something to do with the pre and postcat sensors? Thanks again for your reply zirk

[zirk]

Hi Thankyou for your quick reply. ive just been out and checked the connectors for that part of the loom and all seems fine. i cant find no splits or corroded wires. what does heater circuit open actually mean? is it something to do with the pre and postcat sensors? Thanks again for your reply zirk

The Lambda's (O2) are heated, to aid with them getting up to the correct operating temperature when cold, never worked on a 2.2, so not sure if there 3 wire or 4 wire, but basically 1 wire is O2 sensor, 1 wire is Heater +Volts, and the other is -Volts return or Chassis Ground, or if 4 wire then the other 2 are independent -Volts return from memory. Also the outer case of the sensor is grounded.

If its showing Open Circuit Heater fault code, then the ECU is saying it the heaters(s) circuit is O/C. which could be the Sensor or its wiring. as said with the right tools (DVM or Meter) you can measure the heater loop circuit or check the Voltage feed.

The o2 sensor part (if working) will still work without the heater, but will take longer to operate correctly until up the temperature.

[dandor]

ah, that would explain it, i didnt realise the sensors were heated. Thanks for that. Do you think the sensor i bought may be a dud or the wrong type? its not a genuine gm one but it is an ngk. the guy in the parts place told me he would happily change it but he also said that the chances of it been faulty was slim to none and that it would be the first one in 20 years. Would a bad 02 sensor also trigger the other fault codes and the misfire? Again thank you so much for your help.

[zirk]

ah, that would explain it, i didnt realise the sensors were heated. Thanks for that. Do you think the sensor i bought may be a dud or the wrong type? its not a genuine gm one but it is an ngk. the guy in the parts place told me he would happily change it but he also said that the chances of it been faulty was slim to none and that it would be the first one in 20 years. Would a bad 02 sensor also trigger the other fault codes and the misfire? Again thank you so much for your help.

NGK aren't too bad, but if it was me, I would rather fit a known good VX one, even if second hand than go for a Pattern Parts one.

[dandor]

ok thanks for your help mate i'll get a gm one sorted and let you know how i get on. Dan

[dandor]

Right guys, finally got round to getting a propper gm precat o2 sensor, it has been fitted but im still getting same symptoms which are very bad rough idle at startup when cold. And when its hot im getting an occasional missfire and car seems quite under powered. Ive checked all the wireing for burnt or cracked wires but it all seems fine. Im really at a loss now and any additional info would be greatly appreciated. Thanks to all again in advance. Dan

[C20det]

To be honest I'm getting the same problems with my 3.2 & can't get to the bottom of it all the symptoms you are describing are the exact same as ones I'm getting, very strange tho

Did you ever get the problem sorted on yours?

Regards, Carl

[biggriffin]

You've both got the standard 2.6/3.2 pre-cat problem.
Only cure is get pre cat sensor moved to after main cat (there's a guide) or fit modified 3.0L downpipes.
 

[C20det]

You've both got the standard 2.6/3.2 pre-cat problem.
Only cure is get pre cat sensor moved to after main cat (there's a guide) or fit modified 3.0L downpipes.

Hi

I have my bank 1 & 2 sensor 2 already relocated to after main cat & bank 1 & 2 sensors 1 located in my original sensor 2 slots if that makes sense so if I moved the pre cat sensors as well to after main cat you reckon it should sort it?

Cheers, Carl

[biggriffin]

In plain English.

Move the pre-cat sensor to after the main cat. Leave the sensor that is in front of the main cat were it is.
So when finished,you will have 1 sensor in front of main cat and 1 after it.

[powerslinky]

In plain English.

Move the pre-cat sensor to after the main cat. Leave the sensor that is in front of the main cat were it is.
So when finished,you will have 1 sensor in front of main cat and 1 after it.

Biggriff , I am confused by this as well . . . .   working away from the manifold end of the cat assembly, which sensor should be moved rearwards the first one you come to or the one second.

In the maintenance guide on this it looks like the sensor between the 2 cat bodies is plugged & moved rearwards 

[biggriffin]

1st sensor stays put. 2nd sensor is refitted in new location after main cat.

[powerslinky]

1st sensor stays put. 2nd sensor is refitted in new location after main cat.

I'm clear on it now  . . . Thanks