My friend bought a Volvo S60R a few months ago with a few modifications on it. The car still appears to be in excellent condition except for one issue we have been chasing: a check engine light indicating low voltage on Oxygen sensor 1 (the one closest to the engine).
We have: 1.) replaced the cat-less downpipe with an HPD high-flow catalytic converter downpipe; 2.) Replaced BOTH O2 sensors; 3.) cleaned the mass air sensor; 4.) tested connectors (they appear to function just fine).
The weird thing about the new downpipe is that the second O2 sensor was hitting the driveshaft when we screwed it in, so we had to relocate it with an elbow and an extension.
We tried unplugging the front sensor from the harness and we succeeded in getting a different error code than we saw with everything hooked up.
His phone app, which is capable of monitoring lotsa neat-o things (it's called Torque), tells us "Closed Loop, using O2" with the sensor plugged in and "Open Loop, system failure" with the sensor unplugged.
Torque sees voltage from the rear sensor (sensor 2) but nothing from the front. However, a voltage tester confirmed that we were getting a signal from the sensor! Maybe the sensor is sending the wrong signal?
What should we try next?
Find the vacuum leak. The front sensor is a wide band, so you won't get the same kind of 0-1V signal you see from the rear, you will read lambda. If you look at the correction factor, you will find its over 20%, at which point it kicks a code. Try this- clear the adaptive memory, and start the car. Watch the fuel trim correction, and if its out of range on the input side (vacuum leak, bad MAF, etc) it will start out running a bit rough, then smooth out as the correction factor increases.
Codes that state things like "front o2 voltage low", or "o2 not responding" very seldom mean your sensor has failed. Generally they mean its having to overcorrect for an error in fuel measurement or delivery.
Thank you for the suggestion.
I wonder if the vacuum leak could be coming from the tap where the previous owner ran the boost gauge? That could be a place to start.
In reply to confuZion3:
http://forums.swedespeed.com/showthread.php?166473-OBDII-to-Volvo-Code-Converstion-List
http://forums.swedespeed.com/showthread.php?41379
http://forums.swedespeed.com/showthread.php?146927-O2-sensor-troubles
Also, check the exhaust especially the middle silencer for leaks, they are known to rust and rub up against the driveshaft during rain and snow due to thermal expansion.
Frankly, I think it's probably going to be cheaper and easier to take it to a Volvo Independent Repair shop for a more educated diagnosis.
