95 Tacoma 4 Cyl Error code P0171

snip

What qualifications do you possess to pick and choose through the maintenance schedule?

Since you stated P**** codes, you have an OBDII vehicle.

Those can be a couple of expensive codes, alright, and I would bet that the dealer's diagnosis is most probably correct. That's assuming that they actually tested the MAF and the cat before delivering the bad news, both of which would take a competent technician less than 20 minutess to determine. But anyway, we do see these codes on your model of truck (not inter-related, though) from time to time, with 171 being the MAF and 420 being the cat. Usually. My point, I guess, is that they need to be TESTED in order to make a determination before spending that amount of money. And also, several Toyota models were OBD2 compliant before the mandated '96 model year. Post if you need any more help.

Thanks for your reply qslim,

Are there any tests that I can do on the MAF or CAT? Would an OBD II tester be able to perform these tests?

Do you know if the MAF was used on other years or models? It might give me a better chance of finding one in a junk yard.

The part numbers on the MAF are: 22250-75010 AFH70-09 5620 was etched into it.

Thanks

Here's what I'd do.

I'd record the codes, then reset them. Then WAIT to see which comes back. Then, I'd consider which code (system) can cause a ripple effect in another code -- assuming there are multiple codes. For example -- not a very good example perhaps -- the gas cap can give a Gross Leak error and a General Malfunction error within the Evaporative Emissions Control System. Two codes that result from the same failure. There are other systems in a car that can do essentially the same thing, throw a code where you would expect it, then cause a ripple somewhere downstream that shows up as another code. (If I wasn't a die-hard top poster, I'd have known before I typed this that you already recorded and reset the codes, but let's keep moving ...)

My guess is you need the MAF sensor, and if you have a screwdriver and pliers, you have the tools needed to replace it. The CAT is probably a ripple of the out-of-whack MAF. You said that you reset the code a time or two, did you get the same codes every time, or did you get a couple of codes the first time, and the same single code each time your checked it yourself?

Also, OBD II _could_ be used in '95 because that is a cut-over year, especially with an August production date. OBD II was required by '96, but it could have been implemented earlier if the automakers wanted to. I suspect you might actually have one of the first OBD II cars, but that is open to debate. And, one would have to be there to know for sure, so I can't sit here and say that you definitely have OBD II. I would not be surprised to find that you have OBD II given the production date you told us.

I'm not sure I'd be comfortable with a sensor from a junk yard. The sensor is not a dealer item, and should be available from any of several different aftermarket parts suppliers.

I wouldn't be so quick to take aim at the CAT. There are no moving parts in a CAT, and there really isn't much that can happen to them. I'd be more inclined to think that a sensor that reports what the cat is doing has failed. And I'd be even more inclined to think that something that should be happening earlier in the combustion cycle is causing the CAT to do stuff that is out of spec.

I thought that I had read something a month or so ago that had the downstream sensor reading whatever it reads in too small of a window. That is, the sample time was too short or something along those lines, and when they changed the firmware to a longer sample time, then the reports of failure from the sensor went away. Maybe I'm confusing Toyota with another maker, but I'm pretty sure I read it in this forum, or in a link that I found in this forum.

Thanks for your input Jeff.

The on'y trouble code that I know is the initial one. I didn't read the codes on all the resets. I couldn't determine if I had an OBD system or an OBD II and I don't have an OBD II reader.

Maybe a couple of trips to AutoZone would be appropriate.

Thanks

Unfortunately the the tests for both of these components require some expensive equipment. To test the MAF sensor you would need a Diagnostic tester with the ability to display the vehicles data list. You can test the sensor directly with a volt meter, but you need the specifics from the RM, and doing so is not as effective as using a tester. Testing the CAT involves the use of a gas analyzer to perform an oxygen capture test. This will tell you how efficiently the converter is doing its processing. In any case, like I said before, a decent technician with the right equipment and a solid grasp of OBDII fuel control should be able to pinpoint the exact cause of both codes in less than an hour.

All of what you say may be true. No one should replace anything without performing basic tests. I was simply saying that often both of those codes point to the respective components, based on past experience. Don't go spending $1500 in parts based on that, though. You should always test what needs to be fixed without exception.

The OBD II connector is located along the bottom edge of the dash board, in the area where your left leg rests while driving. It looks sorta like a printer port on the back of a printer, except it has 16 pins instead of 40. If you can find this connector, you definitely have OBD II.

Let's explore this a bit. OBD II was mandated to be in place by the '96 model year. '96 models went into production in the late summer of '95, and I think you said your truck was built in August '95. You got one of the last '95 production trucks - your VIN is definitely '95 - but they build cars with parts that are on the shelf, and they might have finished up '95 production with '96 parts, especially if there was no significant change in '95 and '96 models -- which I think is the case here.

Here is some follow up:

After I cleaned the MAF, the Check Engine light came on again, so I looked for intake leaks. One of the intake plenum clamps was very loose. It looked like it had been put on, but not tightened at all. I tightened it and cleared the trouble code, by pulling the EFI fuse. After a few starts, the Check Engine light came on again. ARGH!

I went ot AutoZone. They had to be convinced that my 1995 Tacoma was OBD II compatible, but eventually they connected their OBD II meter and read the error code.

It was P0420 which briefly means "Catalyst System Efficiency Below Threshold". I asked him to clear it. He was reluctant but eventually he did clear it.

I have driven about 100 miles since the P0420 was cleared and have started the truck about 20 times and the Check Engine light has not come on (yet).

Now the second part of the mystery. How did the intake plenum clamp get loose? I have not done any maintenance on the engine recently. On August 26th I had the oil changed at 83,196 miles. On September 21st the check engine light came on for the first time. Now I have just 83,

Maybe it is just a coincidence.

Thanks for all your constructive input.