Howdy folks--

I've got a fantastic old 1989 Volvo 245 that I love to death. I do most of my own work and can typically keep this car happy.

Just recently I had the Check Engine light come on. I checked the code and it was 2-1-2, Oxygen Sensor. I was surprised because the car runs fine, MPG seems normal, idles/drives like it always has.

So I checked the voltage from the O2 sensor and it wasn't reading anything, so I figured it must be shot........so I bought a new (expensive) Bosch unit from IPD, this morning I installed it (no problem), cleared the code.......and what do you know? The check engine light eventually lit again.

Well now I'm bummed because I flushed some money down the toilet (although the O2 sensor I pulled out was VERY black/dirty, so at least I got a good new part in there).

I've read that a vacuum leak can trick the ECU into reading this code. I'd be surprised that I had a leak since the car runs/idles so well, but who knows?
Also I've read that it can be a connection issue....I can't find a wiring diagram but I've read that the O2 goes through the fuel pump relay behind the glove box? Can anyone confirm?
I've also read that it can be an ECU issue........I have no idea what ECU I have.

Well folks there you have it. I'm not SUPER concerned because the car runs fine but I certainly want to have the Check Engine light cleared in case something serious comes up.

Any ideas would be great, thanks!

DeeDee

 

you should have LH 2.4 fuel injection, and EZK 116 ignition.

according to the table i use, 2-1-2 - Signal missing/faulty from oxygen sensor = Wiring fault to heated O2S sensor - High fuel consumption, driving problems

the proper test is to take a thin strand of bare copper wire, open the one pin connector to the O2 sensor (said connector should be near the wiper motor), and wrap the end of that wire around hte pin, and plug it back in. wrap the exposed bit of this copper strand around the + probe of a multimeter in DC Volts mode, connect the other probe to a reliable ground (the grounding screw for the wiper motor should be nearby). now start the car and let it idle til the temperature gauge starts to approach the middle. you should see a signal that swings from around .1-.3 volts to around .6-.8 volts and back, every couple seconds. the precise voltage doesn't matter, just that its from a value below 0.5 V to a value above it. What counts is that its swinging back and forth. if its doing that, the motor is in good lambda. if its not doing that there could be multiple reasons, from wiring harness issues, to excess air getting into the intake, low fuel pressure, etc.

 

Power to the O2 Sensor comes from the main relay which is also the relay for he fuel pumps and some other equipment.

there may be a leak before the O2 sensor in the exhaust system as well, pulling in fresh air. My guess would be a rich system however.

 

Oh I didn't know this was the procedure for checking the wiring, for some reason I thought I could check at the green wire, where the wiring bundle from the O2 sensor goes in to the firewall then in to the car.
I guess I'll pop the glove box this weekend and see the main relay/wiring situation, see what happens.

Mk

 

i dunno the wire colors, but the O2 sensor should have had two connectors, one with 1 wire and 1 pin, and the other with 2 wires and pins. the wiper motor is on the engine side of the firewall, these connectors aren't far from it (under and a bit to the middle ? its been a couple years since I was there, our 240 is 7 hours away at my daughters)