I have a 2000 Montero Sport 3.0 Liter that has just failed it's smog inspection here in CA due to some engine faults. The tech at the smog shop said that the faults indicated bad oxygen sensors so I have just replaced them (all 4 of them!). However, I now need to reset the engine fault codes. I used to be able to borrow an OBD reset tool from the nearby Auto Zone parts store but when I went there today they told me that they can no longer loan or rent the rest tools.

The guy at Auto Zone mentioned that there might be an easy way to reset the code like disconnecting the battery for a while and such. Does anyone know if there is a way to do this without going out an buying a $200 OBD tool?

Thanks!

 

You cannot reset OBD codes by disconnecting the battery. Whoever told you that at AutoZone knows nothing about OBD. Try other places that offer free OBD code reading and see if they'll reset it for you (Midas?) Once they are reading the code, it only takes the push of one button to reset.

If the cause of the error was really fixed, I think the lamp should have gone out by itself - or it will reset itself after the required driving cycle - could be a few days depending on how you drive. Do you know what error codes you had/have?

$200??? I bought an excellent code reader from Kragen/Checker/Shucks for $60 3 years ago. One of the best investments I made. You may want to shop around.

Good Luck.

Ron

 

This is the Sears version of the one I bought: http://www.sears.com/shc/s/p_10153_1...0928000P?mv=rr

If you search Innova OBD and you might find it for less.

Ron

 

Thanks for the info. I didn't think the code could be reset without a special tool.

BTW, the link you sent for your OBD tool is for a "READER" and that's all it does. It doesn't say anything about being able to reset the fault codes. What I found several years ago when I last looked at these was that the readers are plentiful and cheap but the ones that will actually reset the fault codes cost the big bucks!

 

Not true.

Sorry - now I see that the Sears link I sent did not have a complete description but here is the same product with a better write up:

http://www.carparts.com/INNOVA-OBD-I...=10618-2011191

Note this sentence: "Turns off "check engine" light, clears codes and resets monitors."

This is exactly the same as mine and I've reset my CEL many times with it.

I've been thinking about your post. If the smog station failed you, was the CEL on before you went for the test? If so, why did you go for the test? If the same shop advised you to change out the O2 sensors and then performed the work they should have given you back a truck with no error codes and repeated the smog test for free.

So perhaps you replaced the sensors yourself? In any case I do believe the codes would have been cleared once you solved the problem. We need to know what codes you had. There are quite a few posts about Codes P0421 and P0431 which have to do with failed cat converters, not bad O2 sensors, but many people, and inexperienced shops, go right for the O2 sensors when the cats are the problem. I've had to replace both my warm-up cats at around 170K miles but have never had a bad O2 sensor in 190K miles.

Ron

 

I reset codes all the time by removing the battery terminal. Simply put the key in the ignition to drain any excess power, and shazam you're good to go.

 

Thanks Sebba, you're right and my initial answer was incomplete. Disconnecting and draining will work as long as the cause of the fault has been fixed. If not, the light will of course come back on after a few cycles.

If don_zz's O2 sensors were the only problem - and they were successfully replaced - the ECU should turn off the CEL as soon as the truck has been driven in the cycle(s) required by that part of the program.

Conincidentally I'm going through the same thing with my wife's Discovery. Amazingly, she managed to leave the gas cap loose (again!!) two days proior to the registartion renewal deadline - which requires a smog test. I reset the light with my scanner and am now driving the truck all over the place to try to complete the cycle. The OBD scanner I have shows the status of each loop of the program and even if the lamp is off the smog station will fail it if any of the tests are incomplete. Draining the ECU memory as you suggested is my back up plan.

Ron

 

Let me try to answer all of your questions...

Thanks for the revised link to the OBD reader. It looks like a perfectly usable tool from the description and since you appear to like it, I'll just go order myself one. They've obviously come way down in price since the last time I shopped for one.

Sebba has the answer I was originally looking for but jrmdir's statements about the faults resetting automatically after some period of driving will also work. I'd rather not disconnect the battery and have to put in all the radio codes and channels and such again.

To answer the rest of your questions, let me start from the beginning. When the "Service Engine Soon" light came on a few months ago I was told by another "mechanic" that it meant that it was time to replace the timing belt. I'm used to the "Check Engine" light that the rest of my cars have so I accepted his explanation. When it came time for the smog check, I didn't think anything of it and took it to a "test only" station (as specified on the renewal notice). Not being a repair shop, they did not have a reset tool and could not help me (although I will get the car retested for free).

So being pretty adept at auto repair (I was a factory trained BMW mechanic WAY back when I was between colleges) I didn't think much about replacing the sensors myself. I've done it on all my cars generally without any fuss and the Montero was no exception. A few of them weren't the easiest things to get to but most of the time was spent splicing in the factory connectors to the generic Bosch sensors that I bought.

So I now have a car with 4 brand new sensors that needs to be reset and driven some distance (100 miles is what the guy at the smog station said). I'm going to be driving about 1,000 miles this next weekend so it should sort itself out during that time. A colleague of mine at work also volunteered his OBD reset tool so if he brings that in before the end of the week, I'll go ahead and use it to reset the sensors before the trip. If not, I'll just go this weekend.

The fault codes that were read are:

P0173 - Fuel trim malfunction (bank 2)
P0170 - Fuel trim malfunction (bank 1)
P0421 - Warm up cat efficiency below threshold (bank 1)

The car actually passed the emissions part of the test so the cat seems to be working pretty well, even with the bad O2 sensors. The mechanic at the smog station concurred with that assessment and said replacing the sensors would almost certainly take care of the whole mess.

Thanks for the feedback!

Don

 

those codes are not O2 codes. you need to replace the cat on the passenger side and check for an intake plenum or hose leak.
have you removed the intake at all lately?

 

Thanks for all the info Don. Sorry to tell you this but it's what I feared and I have to second what mitsupartsman said. P0421 is the code for a bad warm-up cat, bank 1, passenger side - period. I went all through this last year when I had the same code. Took it to a Mitsu Dealer who put in on their deep analyzer tool (MUT) and was assured that it was not the O2 Sensor. They replaced the cat ($1,000) and it fixed the problem. This year, like clockwork the other side failed and I got P0431 (driver's side) I replaced the left pre-cat myself for $530 parts only. Again, this fixed the problem.

Since then I found an OBD write-up I can send you that explains that the
P0421 code is from the cat test cycle which the ECU cannot even start unless all the O2 sensors check out OK.

Since you seem to be one of us DIY types, the best approach IMO, is to buy the factory part and install it yourself. Don't know what mitsupartsman.com has but there are a few dealers who sell at discount: www.mitsubishiparts.com is one.

As to the other codes, I have to defer to Mitsupartsman. If you search Montero P0170 and 173 there seems to be mention of lots of reasons including wrong O2 sensors.

Ron