ECM-400C Three-way catalytic converter efficiency

[Pittsjock]

Gents:

The wife took her 2007 XC70 (195k) to get inspected and failed to mentioned to me prior that the CEL had just gone on. The car failed.

The car has had recent PCV service, a cleaned oil pan/sump and runs nicely. Gas mileage is reasonable for use at around 22 (mostly short trips at less than 50 mph). Gas mileage pops up to 23-24 on highway. The car has a little oil leak that I am chasing, but I don't think burns much oil.

I pulled the codes with VIDA and got ECM-400C Three-way catalytic converter efficiency, bank 1, Signal too high. There are no other codes on the car.

Both oxygen sensors are giving readings and based on my research, seem to be within spec. The front is ranging from around 1 to 15 and the rear is cycling between about .16 and .99.

Anyone have any suggestions for the next level of diagnostics? The car is pretty high mileage at this point - 195k, so I guess the catalytic converter could be toast, although this does not seem to be a common failure.

[JRL]

Read my reply on XC70.com

[abscate]

Clear code, drive for a week, res test and pass. Unless the code comes on back in 200 or fewer miles, use this to pass smog until car EOL

[Pittsjock]

Thanks Abscate, but the code comes back too quickly because some test is not completing. I think this points to a sensor/wiring/circuit type issue...?

[abscate]

If it can't complete the O2 sensor test ,I would check wiring and for 12 VDC on the heater

This should show up as a different code than cat efficiency though

[Pittsjock]

No other codes...???? I will check wiring.....TY!

[JDS60R]

front is an A/F sensor -little diff from O2 but same principals apply.

The front s happy at 1 I am assuming you meant 1.5 vs (15) in your post. If it is 15 we have an issue. (should never go over 5) Would also like to know it goes below 1 every once in a while. If VIDA says sig to high and you are seeing 15 then you know what to replace. Sensors are on sale on ebay amazon FCP right now for about $86. I always buy and install both front and rear as they both add to controlling fuel trim

The rear should run .6 on level ground ,steady state ( like 45 mph on flat road with cruise control on.

[Pittsjock]

The front s happy at 1 I am assuming you meant 1.5 vs (15) in your post. If it is 15 we have an issue.

The rear should run .6 on level ground ,steady state ( like 45 mph on flat road with cruise control on.

Thanks JDS. So, I did mean 15....mostly it is hovering between 1 and 5, but if you run the engine up to 2.5 to 3k rpms, and then let off the throttle, it will spike up and then return to the lower numbers.

If you watch the rear sensor in VIDA, it goes from .1 to .9 or so in a pretty steady up and down. From what I read, this is normal?

I inspected both the front and rear sensors and did not see anything particularly abnormal. For some reason, the code cleared and the CEL went off this afternoon. It also cleared in VIDA and the DTC test came up green.

I need to do a bit of maintenance on this car anyway so it sounds like new O2 sensors (front and back) are in order.

Thanks again for the help!