Steve Weldon

I have a 1992 Toyota Pickup with the 3.0 V6. It tripping code 24, "Open or Short in intake air temp sensor circuit for 500msec. or more (THA)"

Am I wrong in reading this to be a "sensor circuit" vs. just a sensor I can easily test/replace? If so, what is in this circuit and how do I test it? And if not, where is this sensor and what is the part number?

Any help would be appreciated.

Thank you.

scope103

For all answers, The Good Book you must read: http://web.archive.org/web/201003261...92volumeai.pdf

The intake air temp sensor is in the VAF, and is not separately replaceable (well, you can DO anything, but there is no part number for it). You are wise to note that the problem is in the "circuit"; no diagnostic code can be read as telling you "replace THIS part."

So the first thing to check is the connector to the VAF; make sure it isn't loose or messed up. Pull the connector, and run the tests given in the FSM cited above. Let us know what you find.

And just in case:

Steve Weldon

Thanks! I have a used OEM MAF on the way, should get it Monday. I'll update you then.

Charchee

I don't know why in the world they would have designed them this way with the two screws that just beg to be pulled out. When I bought my 89, the MAF was trashed from someone fooling with those screws trying to remove the connector. It will come all to pieces if you remove the screws and pull on the cable.

You might also take a peak inside the air flow channel and see if the little gate is moving freely. I've seen them get stuck open which, I would think, could give you a constantly open fault. I use a special MAF cleaning spray now and then to clean mine on both of my Runners. The 3.0 and 3.4L engines use a completely different kind of MAF but the spray seems to work well on both and will make my 3.4L run better and idle smoother every time I do it.

scope103

If you are thinking of code 31 or 32, you SHOULD not get either of those with a stuck vane. A stuck vane would make the truck accelerate poorly when cold (open loop), but it should clear up as soon as the truck was warm enough to go into closed loop.

IF you are going to open up the VAF, checking the vane is probably a good thing to do. But for me, I would never open a VAF if it passed the diagnostic tests.

The tests that, it seems, Steve Weldon chose to skip.

Charchee

That's right. I was trying to help another guy with an open loop symptom at the same time and got the two threads tangled up in my head I guess.

How does the engine run when the CEL is on with this code by the way. Are you having any issues other than the CEL?

Steve Weldon

Update - The wrecking yard got in the MAF yesterday and what a ratty looking corroded piece it was. But still, at $65 it as somewhat of a bargain and when it comes to electronic devices I'd much rather have a used OEM Toyota part, than a who knows where in China it was made part.

Immediately things got better. The idle which was all over the place, the tach showing zero one moment, 300 the next.. you could hear it idling high through. The engine would stumble when accelerating, hard starts, no starts, all that and code 24 are gone. I couldn't be more thrilled. Thanks everyone.

Here's some things though. The old one tested good several months ago, a month ago, a week ago, and today.. yet obviously it was bad.

Once code 24 went off.. I was now getting code 21. It wont' stay on, but it won't go away either. It will stay on for 15-20 minutes, then off for 10.k It cycles. I changed the o2 sensor 405 months ago wiht an OEM Denso. Is it possible with the engine so poorly tuned because of the bad MAF, that the o2 sensor ended up with "stuff" on it that has yet to burn off.. or maybe it needs cleaning? I'll remove it this Friday and test/clean it.. maybe replace it if it tests bad. The wiring loom plug is also worrisome so I'll take a good look at that also..

Sure is nice to have the truck running well again. Thanks!

Steve Weldon

Today the new 02 sensor came in. So I wire in a new harness (and double check it) and new sensor, clear the codes, and still an 02 fault. What else coudl this be? Vacuum leak?

scope103

It will help if you stop calling it an O2 fault. It's much more specific: "Open or short in heater circuit of heated oxygen sensor for 0.5 sec.or more.". http://web.archive.org/web/201211190...85diagnosi.pdf Note the word "circuit"; while that code is often traced to a bad heater in an O2 sensor, it could be anywhere in the circuit.

You could check the heater on your new O2 sensor: http://web.archive.org/web/201003261...01heatedox.pdf . It's easy to do, so why not? (inspection of the feedback voltage is a good idea if the sensor is not working quite right, and as you can see from the manual bad sensor performance CAN produce a code 21 under certain circumstances w/o a heater issue) But the other part of the heater circuit is the harness. Check to be sure you have 12v on the harness side between HT and B+.