P0171 code

I have had the p0171 code for about 6 months now. I’ve replaced the fuel filter, checked for vacuum leaks, cleaned the maf, replaced the intake elbow. I was wondering anyone else has had this issue. I guess I’m going to start replacing sensors now. Does anyone know of any tests I can do to determine if the A/F sensor or maf is bad? I don’t have an obd2 scanner that shows fuel trims but I do have a voltmeter.

thanks,
Eli

 

I got this code and the culprit was the vacuum switching valve.

 

I had a dirty MAF sensor; however she wasn't showing any codes at the time as I remember. Symptoms were pinging under power/ load; then little flat hesitation spots at high speed; like a lean fuel or clogged filter . After checking my fuel pressure , it was spot on. I bought a scanner, and my fuel trims were high. All this lead me to a forum thread that suggested to clean the MAF. Have to reach down in a spot with a long screwdriver on a rag with some brake cleaner. And be careful . It was magic, just scratching some black crude of the sensor!

 

If you're cleaning your MAF with a rag on a long screwdriver covered with brake cleaner, you should definitely look up how to properly do it.

 

Perhaps it wasn't the text book method, as I also read. But that was over 60k miles ago, and still working fine; and cheaper than a new MAF. If you could direct us in the proper method, I would appreciate it. As I remember the P0171 code was for a lean condition , which could indicate multiple suspects. Just my 2 cents , since I spent months tracking my specific issue down.

 

Remove the MAF, disconnect power supply, spray with MAF cleaner (not brake cleaner), let dry, reinstall. Never physically touch the wire.

 

I've done this already. Does anyone now how to test the af sensor

 

I think it would throw a different code if it were the af sensor. Mine just went bad and it didn't give me P0171. I could be wrong though. I'd test the vsv valve to make sure it's working.

 

How would I test that?

 

I cleaned out MAF and replaced air/cabin filter light came back on week later. Swapped MAF w my other toyota and put in 1 bottle of techron complete fuel system pumped 91 light came on 2 wks later. Then put in 1 bottle of gumout high mileage fuel injector cleaner no CEL now. Say what you want about the fuel system cleaners but it seems to work for me. I probably would of changed the sensors if that didn't work then take to mechanic last resort.

 

Do a Ohms test with a multimeter.

 

Thanks @Timmah! . Do you think the af sensor could be causing the p0171 code? Or do you think it’s something else

 

I think there's a chance it's the MAF. Did you clean the two little sensor wires really well with MAF cleaner? It's not the bulb looking thing. That's what detects the temperature of the air coming in the intake. You want those two tiny wires cleaned.

You can also test the MAF.

 

I really appreciate the pages from the FSM. Ill test those tonight

 

Not sure what kind of OBDII reader you have, but if you can connect it to a app like Torque it can help you troubleshoot too. I was getting a P0171 too. The symptoms where hesitation at higher throttle especially going up a hill or with a lot of people in my truck.

Here is what I saw on the Torque app.
The X-axis is time. From the throttle position, you can see I floored it. The MAF g/s rose to about 88g/s. The 02 1x2 V sensor dropped to zero.


Since the MAF sensor had over 150K on it and the previous owner used a K&N air filter and I could see some of the red K&N oil in the intake, I just replaced the MAF.

$96 Denso 197-6020 Mass Air Flow Sensor, Regular

Denso 197-6020 for about $70 on Amazon.

After the replacement was in, I could feel the difference and the Torque app showed this.
MAF g/s now near 120 and the O2 didn't drop to zero.


The original MAF was obviously under reporting air flow.
Since you cleaned the MAF, I would think that would have improved the problem if the MAF was the problem. It will be interesting to see how your MAF tests out with an Ohm meter.

 

I will let you know tomorrow. Ran out of light this afternoon :/

 

Well @Timmah!, I tested the maf and af sensors this afternoon. The af sensor came back at about 2.3 ohms. When I touched the contacts on the sensor it would jump up to around 60 ohms then come down to 2.3. On the maf it was about 2300 ohms. I tested both after the truck had cooled off for about 45 minutes. From looking at the FSM pages you sent it looks like both the sensors are ok right? Any suggestions on what to try next?

 

At ambient temp, the A/F sensor should have fell into the .8 to 1.4 ohms range. 2.3 ohms is outside the spec. Maybe check it again when the exhaust is all the way cold and see what you get. If you get the same value, it's outside the spec and I would replace it. If you use my video to replace the sensor, make sure you read the video description.

https://www.youtube.com/embed/CtngAVxJxkE

 

Ok thanks, how long would you wait after driving to check the sensor?

 

I was also wondering, does the key need to be in the on position or anything?