Diagnosing bad MAF (P0171)
07-16-14, 12:48 AM
#16
Whoops, now that you mention it, I probably am thinking of the IAT sensor bulb (the amber colored bulb that is clearly visible in the MAF). But I also cleaned the two little wire elements that are hidden deep within the recesses of the MAF. So hopefully that's all there was.
07-17-14, 11:45 AM
#17
Driver School Candidate
Thread Starter
Hi all, hoping someone can help by providing some measurements from a working RX300.
Background: I am getting a solid CEL with code P0171 (Bank 1 Too Lean). Having seen many posts identifying a bad MAF (mass airflow sensor) as a possible culprit for P0171, I'm trying to systematically test the MAF to diagnose whether it is bad. I'd prefer not to just replace the MAF unless I am pretty confident it is the culprit. (See my prior ClubLexus post here.)
I have a RX300 repair manual that describes some diagnostic steps for determining whether a MAF is bad. One of the steps it describes is testing the resistance of the MAF's IAT (Intake Air Temperature) sensor. Below are the relevant excerpts from the repair manual. I tested mine and am getting between 5,000-6,000 Ohms at ~ 76 degrees Fahrenheit, when it should really be closer to 2,000-3,000 Ohms.
Can anyone else check the resistance they are getting with a known good MAF and let me know? Should only take a couple minutes and all you need is a (Philips) screwdriver and a multi-meter.
Thanks!
P.S., I have already cleaned my MAF so that should not be a factor.
Background: I am getting a solid CEL with code P0171 (Bank 1 Too Lean). Having seen many posts identifying a bad MAF (mass airflow sensor) as a possible culprit for P0171, I'm trying to systematically test the MAF to diagnose whether it is bad. I'd prefer not to just replace the MAF unless I am pretty confident it is the culprit. (See my prior ClubLexus post here.)
I have a RX300 repair manual that describes some diagnostic steps for determining whether a MAF is bad. One of the steps it describes is testing the resistance of the MAF's IAT (Intake Air Temperature) sensor. Below are the relevant excerpts from the repair manual. I tested mine and am getting between 5,000-6,000 Ohms at ~ 76 degrees Fahrenheit, when it should really be closer to 2,000-3,000 Ohms.
Can anyone else check the resistance they are getting with a known good MAF and let me know? Should only take a couple minutes and all you need is a (Philips) screwdriver and a multi-meter.
Thanks!
P.S., I have already cleaned my MAF so that should not be a factor.
12-07-14, 05:39 PM
#20
Driver School Candidate
Thread Starter
Yes, I think it was. I did some testing of the MAF using a voltmeter, per the instructions in the Lexus service manual (see my earlier posts in this thread). It was giving bad / out of band measurements, so I figured it must be bad. I bought a MAF pulled from a working RX300 and dropped it in. That was several months ago, and haven't had P171 come back. The weird thing was, the used MAF that I bought was giving roughly the same bad / out of band measurements on the voltmeter when I tested it. But it worked in making the CEL go away.
12-08-14, 03:07 PM
#23
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