OB99W

A 2005 is less likely than your 2000 to have bad HGs, but for the sake of this discussion, let's assume that they're the likely problem. In fact, let's assume that HGs are 10 times more likely than the radiator cap to be the problem. However, HG replacement at a typical shop is about 100 times more than the cost of a radiator cap. It's certainly worthwhile cleaning or replacing the cap, especially given that Subaru TSB 09-45-06 (which I linked to above) covers this specific possibility.

Is the car being parked outdoors, or in a garage? If the latter, I can tell you what worked for me when I had the same problem.

It would not be typical for a recent Phase-2 2.5 to have an internal HG leak. As both you and davebugs mentioned, the radiator cap is something to consider first. Since the problem became obvious just a few days after service at a dealer, it might be related to that work. While doing an oil change, most techs will check other fluid levels. If the radiator cap was removed, and some contaminent got into the cap seal area, it might be the cause of your problem. If the seal is compromised only a little, it could take a few days of the coolant expanding into the reservoir and not returning to the radiator for it to overflow. I'd start by thoroughly cleaning the cap, including all the ''nooks and crannies'', and check for any irregularities in the seal. Also, clean and inspect the radiator neck, especially sealing areas. There was a TSB on this topic... ...okay, I did a Google search and found a link: http://www.thel7.com/TSB/09-45-06.pdf .

The ''46'' code you previously mentioned was likely misread, and is probably ''56''. ''56'' is ''Abnormal G sensor output voltage'' -- that's ''G'' as in ''gravity forces''. The code doesn't necessarily indicate that the sensor itself is bad -- it could be a connector/wiring issue. The ABS valve relay is inside the ABS control module. While it's certainly possible to have two separate ABS problems, you should still verify that the battery voltage isn't low, since that can sometimes cause the control unit to misbehave.

I don't have a listing for ''46''. ''51'' is defined as ''Abnormal valve relay''. However, ''42'' is ''Source voltage is abnormal'', and that should probably be dealt with first. It could signify a battery/alternator problem, a connection/wiring problem, or possibly just that a fuse was pulled. First, check the battery voltage, and if it isn't normal do what's necessary to take care of that. Next, I'd suggest starting with clearing the ABS memory so that the codes can be checked again. To clear the ABS memory, connect a ground probe to B82 pin 6, and turn the ignition switch ''ON'' (don't start the engine). You should get the codes, as before. Then pull the probe from pin 6 and quickly reinsert it three times (you have to complete that within 12 seconds or so), leaving it in pin 6 the last time. You should then hear the ABS unit sequence (expected when codes are cleared) -- allow it to complete the cycle. After turning the ignition ''OFF'' and then ''ON'' once more (again, not starting the engine), the ABS codes can be read. At that point, you might just get the ''11'' code, or more. Recheck codes after another drive, and post what shows up then.

I don't know anything about the Bosal cats, but I was curious. I found them at: http://www.partsgeek.com/catalog/2000/subaru/outback/exhaust/catalytic_converter.html . Do you know which model you'd be getting, and what the performance difference is between them -- the selling price certainly is different, and not just at this particular website.

Here's the previous thread: http://www.ultimatesubaru.org/forum/showthread.php?t=99926 I came to the same conclusion about the CTS in my post #5 in that thread. More to the point, in the earlier thread Roamer said that the problem was immediate upon cold start. Since the ECU runs open-loop and ignores the O2 sensor until things warm up, how could that sensor be the cause of the complaint? The O2 sensor (presumedly front one) might indeed be sluggish, but something else (probably the CTS) is the likely culprit.

Good question. With all the other recent threads on this topic, I forgot to ask if this one was a '96. Well, a '96 can complete the I/M monitors and be ready after a proper drive cycle -- but it won't retain that once the engine is shut off. If the car we're discussing in this thread is '96, see the links in my posts here: http://www.ultimatesubaru.org/forum/showthread.php?t=99635 .

An aging O2 sensor can cause the mixture to run rich, but that doesn't usually lead to misfire. However, at significant altitude (where the air is ''thin'') it might be possible for that enrichment to be sufficient to cause rich-misfire. Properly diagnosing the problem should probably include an OBD-II scan tool, looking at sensor performance, fuel trims, etc.

You can probably get away with a less exacting drive cycle. See: http://findarticles.com/p/articles/mi_qa3828/is_200511/ai_n15871211/pg_3/ They're the people who design the car while having to contend with EPA regulations, among other things. The drive cycle that includes ''30 minutes of 55 mph without the throttle angle changing'' is suggested for the fastest way to be assured that all the monitors will be ready, but it obviously isn't the only way to accomplish that.

Proper drive cycle(s) will result in the I/M monitors status changing to ''ready'', as long as the ECU doesn't detect certain faults during the cycle.

Your '97 ''Postal'' is behaving like it has a '96 ECU in it-- perhaps it's an early-production unit. See the links in my posts here: http://www.ultimatesubaru.org/forum/showthread.php?t=99635

Still, requiring a quart of oil per 600 miles is significant. However, in addition to any that's burned, a small leak could account for part of that. As has already been mentioned, burned oil typically produces bluish smoke. A well running engine burns (''oxidizes'') the vast majority of the fuel. Properly oxidized carbon becomes carbon dioxide, while somewhat insufficient oxidation results in carbon monoxide. Really insufficient oxidation produces soot (mainly small carbon particles). So yes, black smoke is usually carbon, and indicates incomplete combustion. It's sometimes hard to tell from the color exactly what the source is -- black-ish smoke could be from a combination of incompletely burned fuel and oil.

You're welcome. It does seem like the neutral switch itself (or its operation/connection) is the likely cause of the code in your case -- the ECU thinks the car is in neutral when it isn't, and acts accordingly. When the ECU triggers the P1507 code, it also puts the system into a ''limping'' mode, and that's probably the poor-running condition you experienced.

You're welcome. While you're at it, verify that the PCV valve isn't sticking open -- that can have the same effect as an intake air leak (leans the mixture, possibly causing misfire).

Check for intake air leaks, and also see this: http://endwrench.com/images/pdfs/DiagTroubSum04.pdf .

A good compression reading will confirm that the valves are closing (sealing) correctly. However, compression testing won't reveal if a valve isn't opening sufficiently, unless the condition is very severe. (Intake valves not opening enough could require more crank rotations to build up cylinder pressure than on cylinders with correct valve adjustment.)

One possibility is an intake air leak. That would have the most effect at idle, since at higher speeds/loads, the larger volume of air being used by the engine ''swamps'' out the leak. Much of the time, EGR valve problems are from the valve not opening or passages being blocked with carbon. However, if the EGR remains open more than it should, that can cause misfire, and sometimes doesn't trigger an EGR code.

Not necessarily -- the ECU can ''believe'' the engine temperature is what the CTS reports.

You seem to be describing an A/F mixture that is too lean. A common cause of cold start/running problems is a defective CTS (coolant temperature sensor). Of course, since the engine requires a richer mixture than usual when started cold, something else that doesn't allow for the right ratio could cause similar symptoms.

Could you clarify the oil consumption? Does ''1/4 of oil'' mean ''1/4 of a quart of oil'', ''one quart of oil'', or ''1/4 of the engine's oil capacity''? The first would be equivalent to one quart in 2400 miles, which wouldn't be terrible. Either of the other two would be significant oil consumption.

If you reread my post #4 in this thread, you'll see that I suggested some possibilities for P0420 other than actual catalyst inefficiency. (And yes, the front O2 sensor should be Subaru OEM -- it can make a difference.) A competent mechanic should be able to do a diagnosis that will either confirm alternatives or rule them out. Here's more info, including some causes of P0420 to consider: http://www.catalyticconverter.org/news/news_page.cfm?Key=codes-po420-po421-po430-po431&News=120 By the way, I have no particular predjudice for OEM parts, other than when experience shows it makes a difference in certain applications. Sometimes the advantage is performance or longevity, and sometimes it's just that a part fits without having to ''modify'' or ''persuade'' it.

Your profile says ''New York'' for the state -- please let me know if it's anywhere near Ithaca, so that I can stay off the roads until you get around to installing the switch.

There's another dynamic working when it comes to catalytic converters that you might not be considering. The car manufacturer has to contend with the EPA-mandated emissions warranty for new vehicles. It would make sense for Subaru/Honda/Toyota/etc to use a part that isn't likely to fail during that period. Assuming the OEM replacement is equal to the original, it also should be expected to have a long life. Aftermarket converters only have to have catalyst that makes it 25,000 miles to satisfy the EPA. See: http://www.catalyticconverter.org/news/news_page.cfm?Key=catalytic_converter-&News=20 Still not convinced of the difference between OEM and aftermarket? Then see this, which starts off explaining that ''high flow'' is misleading, and then what the differences are in cells/inch and amount of catalyst used: http://www.catalyticconverter.org/news/news_page.cfm?Key=catalytic_converter-&News=89

See http://www.ultimatesubaru.org/forum/showthread.php?t=99777 , especially the links given in posts #3 and #10 of that thread.