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Discussion Starter · #1 ·
Hi All,
I have a Astra G 1.8 and have been getting a random check engine light coming on. Put the scanner on it and got P0140 O2 SENSOR CIRCUIT NO ACTIVITY - DETECTED BANK 1 SENSOR 2. I assumed sensor #1 is the one before the cat and sensor #2 is the one further back under the car?
The odd thing is that when I checked the live data sensor #1 was showing odd numbers, jumping between 0.135mV then 0.800mV then 0.095mV. Whereas sensor #2 was showing anywhere between 0.410mV to 0.425mV on the 10 minute test drive. Why would I get a fault code on sensor #2 when its reading seems in spec and no fault code for sensor #1 which seems well out of spec?
Could anyone provide some help with this before I spend money on a replacement O2 sensor.
Thanks, BB
 

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Sensor 1 should go from approx 0.1v to 0.9v in a up and down swing.

Get the car warm and record some live data and put some propane into the intake and see if the rear sensor reacts. Also find a downhill and see if sensor 2 drops to near zero on over run. If not then it's probably dead or wiring issue.
 

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Discussion Starter · #3 ·
Hi Marks152, thanks for your response. So from what you said above it looks like sensor #1 is okay (just to clarify that is the sensor at the exhaust manifold). Before I read your reply i captured some live data and saw sensor #2 seems to move normally between .410-.420 apron. but then suddenly would drop to zero for a second or two then return to normal. So I thought it must be a faulty sensor. I replaced it with a new NGK sensor and cleared the code. But after a week or so the check light came on again. Do you think it might be a wiring issue? Do you know how to check the wiring? Thx
 

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Hi All,
I have a Astra G 1.8 and have been getting a random check engine light coming on. Put the scanner on it and got P0140 O2 SENSOR CIRCUIT NO ACTIVITY - DETECTED BANK 1 SENSOR 2. I assumed sensor #1 is the one before the cat and sensor #2 is the one further back under the car?
The odd thing is that when I checked the live data sensor #1 was showing odd numbers, jumping between 0.135mV then 0.800mV then 0.095mV. Whereas sensor #2 was showing anywhere between 0.410mV to 0.425mV on the 10 minute test drive. Why would I get a fault code on sensor #2 when its reading seems in spec and no fault code for sensor #1 which seems well out of spec?
Could anyone provide some help with this before I spend money on a replacement O2 sensor.
Thanks, BB
You may not be aware that the ECU on this models had a history of problems due to being bolted direct onto the cylinder head, and had a lot of thermal changes ie HOT/COLD running causing a lot of damage to the ECU circuit boards in terms shrinkage and cracks in the soldering circuits, that would open up and close at random. causing odd faults .I had an Astra Elegance Auto 1.8 that was a terrific car, in the 9 years I had it I had three ECU"s,the last one supplied was from a speicalist V/X ECU dealer, it was a unit from the Vectra that had been coded and modified/uprated to my car and VIN number, problems solved. and slightly better performance . The o2 sensor readings on the one before this one were the same issues with yours till it was realised that the ECU was causing this incorrect reading of the lamda sensors,and it was staying open all the time and not closing off after a few minutes in the warming up process. I had replaced two lamda sensors thinking they were not compatible with my car,replaced with a genuine v/x ones. same fault, so realised that the ECU was not getting the message .and replaced it once again,and this new was the answer
 
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