DTC P0138 at highway speeds

My first suspect would be whoever replaced it.
In the Haynes manual instructions for replacing it there are some major warnings about special handling and replacement instructions. Evidently the sensor is very fragile and won't tolerate a number of things, especially involving the electrical connections.

 

Shouldn't this replacement have been covered by the federally mandated emissions control system warranty?

 

Canadian gasoline contains MMT (Methylcyclopentadienyl manganese tricarbonyl) which can adversely affect O2 sensors and catalytic converters. The emissions warranty on Canadian model vehicles is generally shorter than US Federal emissions warranties

The ACEA (Association des Constructeurs Européens d'Automobiles)conducted tests and determined that there were apparent increases in emissions - and fuel consumption - by 50,000 miles using MMT gasoline. By 100,000 miles, the difference was significant, especially for emissions

Ethyl Corp - the same nice folks who put lead in gasoline - have an army of lawyers and are always fighting the removal of their cash cow from gasoline.

 

My bad. I did not notice that the OP is from Canada.:doh:

I do know that US laws do not apply north of the border.

 

No worries. Here, have a drink on me

Gluk-gluk-gluk-gluk-gluk-gluk-gluk <clink>

 

Perhaps that gas damaged the catalytic converter?

If the problem is not the sensor, then its likely that the Catalytic Converter might be faulty...

 

There should be two O2 sensors, one before the catalytic, one after. The one after is responsible for performance measurements of the catalytic. This could turn out to be a pricey repair

In Canada, Toyota only provides emissions coverage for 36 months or 60,000 km, with some parts only covered for 24 months or 40,000 km. The 96 month or 130,000 km emissions coverage in Canada has many exclusions

If you're interested, the ACEA has very specific evidence of emissions control equipment damage running MMT gasolines. This is in their WWFC report

http://www.acea.be/images/uploads/pub/Final WWFC 4 Sep 2006.pdf

The discussion of MMT starts on pdf page 26, near the bottom of the page. Many photos are included

 

Just to get technical here... There is only one O2 sensor.... The front sensor is an air/fuel ratio sensor. Much more reactive and sensitive and also much more expensive.....


BTW A/F sensors and O2 sensors are only covered 3 year 36000 miles in the USA. The catalytic convertor is 8/80.

 

Did you provide this TSB information to them?

http://www.vfaq.net/docs/TSBs/EG018-03.pdf

Not sure if you are still in warranty though...

Anyway, having similarly high-way only DTC code (P0420), I can tell you my guess why you are getting your DTC at high-way only. It is that the car computer would not even attempt to perform certain diagnostic tests unless you are driving on the highway after the car has reached certain state. Look at the TSB above for conditions for this code. Basically, your "readiness" status would never be "ready" if you never go thru the compete set of diagnostics the computer does. And that would never happen if you do not drive on the highway. In my case, I could drive for weeks and not get the code but my emissions system check readiness was "not ready". Once I got on the highway, the car went thru the diagnostic cycle and sure enough the DTC would come-up.

Not sure however how to diagnose/repair your problem. Mine was a clear-cut Cat Converter failure so I had to replace the cat converter, reusing the old O2 sensor and it worked great. Btw, the sensor part can be had from Toyota for about $100. Charging you additional $300 labor is a little excessive IMO to replace it...

 

An out of range oxygen sensor would most likely be caused by an exhaust leak. Air (oxygen) getting into the system or the engine is misfiring.

 

This is certainly true for emission systems. If you clear codes, unless the ScanGauge does it somehow differently, the I/M status should *not* be ready immediately. I think . In my '02, after I clear a code my scanner says "I/M status not ready". It is not a scanGauge but a generic OBD-II scanner with "Live View", so similar to ScanGuage I suppose. It takes me several days and highway cycles of 5 minutes over 55 mph to clear all the emission system checks and then the status becomes ready.

Dealer prices I find often are inflated. I have checked the price from ToyotaParts4u.com and I've seen a quote on these forums for another online/phone Toyota dealer at around $109. But this is for the rear O2 on a '01-03 model. Not sure if the rear O2 sensor on the '04+ is different/more expensive though (I think only the front is different on the newer Prii but I might be wrong here).

 

Not in the mood to jack up my Prius, so I will take your word for it. Didn't pay much attention to the catalytics on my FJ, but I thought a month ago when I greased it I noticed O2 after the cats. Perhaps just a truck thing

 

It wouldn't hurt to inspect the plugs, though a misfire should also set a CEL. An exhaust leak, well I wonder just how much effort that Toyota dealer put into fixing the problem.

Using the genuine Toyota scantool, it would have been easy to look at live data and confirm the performance of the O2 sensor.

Additionally, they should have done the drive cycle as suggested by the TSB. If they are only willing to replace parts until the problem is "fixed" it's time for him to find a different dealer

 

True, according to the Haynes manual.

 

Ok checked the TIS manual. Yep, one O2

 

A/F sensor before the cat tells the ECU how to adjust fuel trim. O2 sensor after the cats tells the ECU how well the cats are functioning.:attention:

 

Sorry kocho, but I just checked and that TSB is listed as Obsolete by Toyota. The revised one is EG038-04 and involves reflashing the ECU. Not sure about the dealers north of the border, but here in the states,we are now using a new diagnostic tester, Techstream. It is a notebook that took the place of the previous tester. By going into the Health Check section, any updates for any calibrations will be highlighted here. It is a lot faster and does more then the older tester. According to TSB, the warranty is for 96 months or 80000 miles,whichever comes first. Have the dealer recheck for any updated calibrations, Prius Pete, which may take care of your condition. Not sure if Canada is different in calibrations, but it might be worth a try.