2006 S60, CEL for fuel trim and MAF sensor

[zjevik]

Hi everyone,

Today I got my first CEL and I'm not sure what's the reason. Well, I know what's the reason but I'm not sure what should I do. I hope that someone here will be able to point me to correct direction. Here is the story:

I got the car two and a half years ago and I cleaned the PCV box and tube. Unfortunately at that time, I didn't know that you cannot reuse the intake manifold gasket so I reused it. I bought Vida about 6 months ago and I found out that I have ECM-120D (Ar mass - Signal too low). I didn't pay attention to it because there is no CEL and I thought it's small leak in the intake manifold gasket. The performance wasn't influenced and I had 22 MPG in city so I though MAF is good.

Fast forwarding to today, I got ECM-216D (Long-term fuel trim, bank 1 - Signal too low) together with ECM-21E0(reason for the CEL) and ECM-121B (Mass air flow sensor - Flow too low). I'm not sure if MAF is finally going bad or it's something new I should take care of. My recent MPG went down to 19 driving mostly in city.

Should I measure the voltage at MAF to see if it's out of specs or change it with one from scrap yard? Is there some DIY way of doing smoke test to find a leak? Or would you take it to some indy with a smoke machine?

Here are vida outputs:

Thanks for your suggestions!

[mrbrian200]

When it trips the ECM-121B (MAF-Low) means:
The relationship in closed loop for what the O2 sensor indicates fuel metering needs to be to maintain proper air/fuel ratio is incorrect for the amount of air entering the system as measured by the MAF: the MAF indicates to little air entering for the amount of fuel being used.

If you're not experiencing general drivability issues (stalling, hesitation, surging, rough idle, misfires), then most likely you have a minor/moderate air leak somewhere.

The easy way to find air leaks is with a smoke test. Or you can go over every hose/valve/connection with a fine comb. This includes the PCV/brake booster/vapor recovery systems.

There are other things that can cause these readings to go astray including bad sensors, plugged injectors, failed throttle body, head gasket issue.... But before you go down that path you should rule out an air leak. Depending on the mileage the oxygen sensor is probably suspect. When they fail they tend to indicate a false lean condition.

[zjevik]

Thanks for you feedback Bryan. The car has almost 120k and it was surging for a few seconds when I started it cold today. I did the smoke test and I didn't find any leaks. I connected a smoke machine to this hose:

I was also fooling around in vida and I found that the rear oxygen sensor is going all over the place. Here is a graph I got from almost warmed up car:

Is this normal? Vida says that the voltage should be around 0.6V. I plan on checking the cat when the car cools down.

[mrbrian200]

For the rear one, try unscrewing it, put a fresh dab of conductive anti seize on the threads and torque it back. I've seen a rear O2s work itself loose before on a VW with wild fluctuations like that. If that doesn't settle it down then the sensor itself is probably bad. The rear on only monitor the cat and isn't used for fuel metering. Surging is consistant with the front O2s failing, which is used for fuel metering. If you found nothing on the smoke test @120,000 the O2s is a pretty safe bet.

[abscate]

Thanks for you feedback Bryan. The car has almost 120k and it was surging for a few seconds when I started it cold today. I did the smoke test and I didn't find any leaks. I connected a smoke machine to this hose:
2.jpg

I was also fooling around in vida and I found that the rear oxygen sensor is going all over the place. Here is a graph I got from almost warmed up car:
1.png

Is this normal? Vida says that the voltage should be around 0.6V. I plan on checking the cat when the car cools down.

Can you smoke test upstream of the injector vacuum pump? I think so, but it might be worth trying direct to the manifold , that next connection after the " plastic thing"

[zjevik]

I will try to do the smoke test directly to the manifold when I have more time. The smoker I used last time disintegrated itself by the time I was done I'm quite busy now and I found out that the morning hesitation I described last time was caused by the smoke test. The car drives normally now, I drove it for about 50 miles and no codes came back yet. I'm starting to question if the sensors are bad.

Anyway, I was going to change the fuel filter and found this:

Do you know if I can just cut the line 2in above the filter and replace only a few inches? I really don't want to drop the tank and replace the whole line.

[mrbrian200]

Might not be necessary to drop the tank to replace that line. There's an access cover under the rear seat cushion to get to the pump (and the other end of the line you're looking at) I would bet you can get that out and a new one in without dropping the tank--it couldn't be much more than 12-16 inches long. It would certainly be better to replace the whole thing rather than splicing it. The other end at the tank/pump may look just as bad.

I see your PEM is still under the car. Does anybody know whether he can still get that relocated to the trunk at a dealer as an extended warranty item? I know they extended the coverage for this +6 years/unlimited mileage but I'm not sure which warranty parameter applies.. new vehicle limited which was originally 4yr/50k or whether it's considered an emission (part of fuel system) or corrosion issue (TSB/NHTSA docs specifically state the PEM is subject to "corrosion"). Emission and general corrosion terms are longer to begin with, up to 12 years.

???

[zjevik]

I thought the line goes all the way to the engine bay. If it ends on top of the fuel tank then I will change it. I will hopefully check it over the weekend. I was moving this weekend so I had to postpone this. But I got an idea for a new smoke machine.

I might stop by a dealer and try to ask them about the PEM and what they recommend to do with the line.

I will keep you posted!

[mrbrian200]

My bad. Yes that's the line which goes up front to the engine compartment. I'm not sure what's involved in replacing it. That amount of deterioration does seem premature for only being 10-11yo on a MY06. That hose on mine is getting a little stiff/not as bendy as it would have been new, but not looking anything like its in danger of bursting open as it looks on yours. That also may be of concern for a dealer/VCC to get a look at.

[zjevik]

Sorry I didn't respond for such a long time. I moved and started a new (temporary) job.

I visited an indi and a dealer and show them the fuel line. They both said that if I insist then they can only replace the whole line, they will not splice it. The dealer said that they would leave it as it is if it's not leaking. The indi said that there is a plastic line inside the rubber tube and the plastic line can still be fine.

I put some tape over the line, changed the fuel filter and I will check it regularly.

But let me go back to the codes. My commute was mostly stop-and-go traffic for an hour a day in 90+ weather. Now, I drive 35-50 miles/day, 70% on highway, and the computer mpg is now above 22. I drove more than 1k miles since the last update and the only code that is back is ECM-120D (Air mass - Signal too low). But here are the values from VIDA:

Counter 1 Started operation cycles since fault was last found. 61
Counter 3 All operation cycles since the fault was found the first time. 88
Counter 4 Confirmed operation cycles with active fault. 7
(Short term fuel trim, bank 1 5.47 %)

So I guess I will just leave it as it is and keep and eye on it. Thanks guys for your help! I'm sure I will be back soon