2000 S70 Base Getting 12mpg

[abscate]

I think if the sensors were cooked enough to halve the mileage the short term furl trim would throw a code and light the check engine light , CEL

Diagnostic data would show that though.

[mikealder]

Does the check engine light come on when you first turn the ignition on, if not it could be a blown bulb or even a removed bulb by a previous owner to cover up a deep seated issue - Mike

[thankswww]

Well friends,

Since "fixing" the thermostat in the airbox, and resetting the ECU, I've gone from 12mph city driving to a consistent 15.2mpg. This is still pretty horrible, but at least there was a slight improvement.

The car has never thrown a CEL. Worst part is, the car seems to be totally asymptomatic, other than the horrible gas mileage! No problem with starts or idles, no visible leaks and no smells of fuel. No problem with the thing heating up to operating temp, or not heating up.

I have not yet replaced the O2 sensors. Looking at them, it doesn't appear that the previous owner has ever had them off either (though I'm just going by the exterior appearance of them).

With no other symptoms, it's getting extremely frustrating trying to hunt down the source of the horrible gas mileage. I'm at the point where I can replace the O2 sensors, and hope that does something. This mileage is horrendous.

As a last ditch effort, I will probably order new O2 sensors this evening and hope that this results in some kind of change for the better.

[thankswww]

Hooked the car up to an OBDII scanner just now. These are the results:

P0135: Front heated oxygen sensor (HO2S), preheating Faulty signal. Permanent fault.
P0327: Knock sensor (KS), front **Already ordered this one.
P0505: Idle Air controller?
P0141: Rear heated oxygen sensor (HO2S) Faulty signal preheating
P0443: Evaporative emission system (EVAP) valve. Signal missing. Permanent valve fault
P1671: Volvo CMP Actuator Performance Problem Or Signal Out Of Range

For a car that runs so well and has never thrown a CEL, I'm quite surprised.

Aside from the two O2 sensors, I wonder what else I may need to order to remedy these issues. Seeing as how I need to order all of my replacement parts from overseas, any suggestions on what I should replace aside from the two O2 sensors would be greatly appreciated. Would save me some money on shipping if I didn't have to make several orders in several shipments =)

[mikealder]

P0135 should be throwing the CEL on all the time, does the CEL illuminate when you turn the ignition to on then go out when you start the engine (it should do) if it doesn't the bulb is either blown or has been removed - Mike

[thankswww]

After checking again this morning, you are right! The CEL has been disabled. I'm guessing by the used car dealer who sold me the car.... but perhaps the bulb "burnt out" on its own? Christ.

[Denton]

After checking again this morning, you are right! The CEL has been disabled. I'm guessing by the used car dealer who sold me the car.... but perhaps the bulb "burnt out" on its own? Christ.

Wow. Did you run a car fax to verify the mileage ?

[thankswww]

I'm living abroad,in South Korea. No carfax here. Guessing the dealer disabled it because they didnt want to spend money on sensors and just wanted to sell it. Sadly, I expect this kind of thing here. This is one of the reasons I do all of my own repairs.

[mikealder]

Is the car a Turbo model or normally aspirated, if it is N/A then the pre-cat probe you need is a Denso Dox-1419 which should work out cheaper than the Volvo OEM unit (and it is the same identical part other than the colour of the box it is supplied in).
If it's a Turbo then stick to Volvo/ Bosch for the pre-cat - Mike

[thankswww]

This car is a 2000 non-turbo.

I spoke with FCP Euro and was told that two Bosche plugs would work for my car. Is this information incorrect? I would hate to make an expensive mistake while I can still stop the order.