Volvo Fault code 2-1-2

[Egg-nogged]

Hi, i have a problems with my 95 T-5 estate, its a re-occuring fault code
2-1-2 (Oxygen sensor signal internitant/not present). The fault code will not always appear, but if it does it will normally be after approx 15-20 minutes into a journey (presumably after the ECU has switched over from pre-set ratio to Oxygen sensor signal) with no affect on performance etc. After the fault code appears it can be reset with no problems. Apart from this annoying code the car performs faultlessly. I have changed the oxgen sensor to no affect, i have checked the voltages from the new oxygen sensor and they are correct. I then suspected the wiring, and changed the two signal wires from the ECU to the oxgen sensor, with no affect. I am out of ideas and was wondering if a fault elsewhere on the car could cause this faut code, any ideas would be appreciated, cheers

[White850Turbo]

That certainly is strange. I presume the signal wire is giving a reading of about 0.5 volts at idle? The sensor is OEM Volvo and has the original plug for the sensor? How is the petrol consumption? Perhaps there is a connectivity problem from the sensor wires to the socket. The only surefire way to determine if and when the signal is intermittent would be to run a datalogging setup through the OBD-II port and view the voltage from the o2 sensor.

[matthew1]

Which sensor did you replace? There's two; perhaps it's the other sending the signal .

[Egg-nogged]

Hi, the fuel consumption appears unaffected, as does the performance, there is only one oxgen sensor fitted to my car, its on the down pipe infront of the cat. The sensor is not OEM, however its all wired in ok (have checked it about 10 times!) i used a blow torch on the bench to check voltages with a multimeter and the oxygen sensor performed within limits. It does seem like a bad contact somewhere to me as the fault is intermitant. As you say the best way to check would be while the engine warms up and constantly monitor the voltage. Cheers