jrallan26

My wife was driving in the rain last night. Right when she pulled into the driveway the "check engine light" came on.

The truck runs great, just the light on. Any opinions???

BTW the filter is bone dry.

Rick F.

Go to Autozone or some other auto store and have them pull the code. They'll do it for free. It could be most anything, but if you're running a stock paper air filter, my bet is it's an O2 sensor. That's one of the more common nuisance CEL's. You can reset it by pulling the ECU fuse for a few minutes. If the CEL comes back on then it's probably for real.

jrallan26

Update:

Went to Autozone and they cleared the check engine light. It was a tempature sensor.

Mr. Bob

what was the exact code???

Tacoclimber

Hey Jonathan, my truck did the same thing once when I drove through a pretty deep puddle... After a night of sitting, the light never came on again... I haven't been in as severe a rain storm since, but my guess at the time was it was the 02 sensor or the temp sensor. Just wanted you to know you weren't the only one...

jrallan26

code 128 tempature sensor

boluca

I am having the same problem with the check engine light. Had the code read and it was PO171, System Too Lean Bank 1 which they said was the oxygen sensor before the cat. I changed it out but the same code came back. The oxygen sensor was purchased from NAPA. Could it be a bad oxygen sensor or something else? Truck is a 99 4RUnner limited with 77k miles. Truck runs fine. I have 2 friends with the same problem but don't know their codes. I have checked the throttle body and it looks clean and have used some injector cleaner. Plugs look fine. Any ideas?

jrallan26

Did you clear the code and it reappears?

jrallan26

Did you clear the code and it reappears?

hupptoy

When I had this code, it was my MAF not my O2 sensor, although several shops (including one Toyota that said it was O2 sensor or bad gas...don't use them anymore...) said O2 sensor. 2nd Toyota shop went straight to MAF and it has been fine for years since (BTW, this is b4 I found online forums...)

Do a search on cleaning the MAF sensor and you should find what you need.

Do you have a K&N filter that you recently cleaned and re-oiled? If so, that is probably what caused the problem. If not, then ??

hupptoy

boluca

Stock air filter and it was replaced about a month before the light came on. I had the code read and cleared before and after the new oxy sensor and the light comes back on in about 30 miles. Always the same code, PO171. Of course I checked the gas cap first. Let me do a search on the MAF and see if I can clean it.

MTL_4runner

That is a rare code (P0128) you might want to have a look in the FSM for the troubleshooting procedure on that.

*Edit* Found this for you.....specifically for the 5VZ-FE
http://www.parksoffroad.com/tacomamo...de/cip0128.pdf

gpcollen1

Similar situation here - I had a friend of a friend Yota mechanic tell me it was definitely the O2 sensor - ended up being MAF after replacing the O2. Atleast I know my O2 is new!??!

G

MTL_4runner

I hope you didn't have the same code?

jrallan26

The check engine light showed up again so I took it to the shop. Found out the thermostat was stuck open. Is that bad???

Anyway the truck is getting fixed plus getting everything else serviced.

MTL_4runner

No, that is the best scenario....much better to stick open than closed.

boluca

Update on the PO171. After replacing the oxygen sensor the CEL kept coming back on with PO171, within a few miles. Cleaned the MAF with contact cleaner and the light has stayed off for 2 days so far.

blzorro

How do you know which o2 sensor needs to be replaced since there are two??

MTL_4runner

It will usually say bank 1, sensor 1 for the sensor before the cat and bank 1, sensor 2 for the one after the cat. In this case you always would replace the one in front of the cat first (unless you had access to an OBD meter so you could see the output signal......very helpful tool to have!!!!) since it usually is the first to foul because of higher carbon/oil ash exposure. In the case of P0171 the typical choices are MAF or O2 (but MAF is by far the more common cause of this particular code).