99 4 runner check engine light problem - Toyota Nation Forum : Toyota Car and Truck Forums

steveo64 · 03-31-2005, 03:19 PM

Hi there,

I have had an issue with my check engine light coming on. I have a 99 4 runner limited (6 cylinder) and my main mechanic has had troubles diagnosing it. I get what was called a "lean code" ( P0171 I think). the truck has CA emissions.

My mechanic (that I trust) replaced the air/fuel ratio sensor (PN 234-9002) which is the same as the oxygen sensor on non CA emissions trucks I guess.

My mechanic sent me to the Toyota dealer after a few tries at a fix (after the light came back on). The best that happened was that they (my trusted mechanic) had cleaned the Mass Airflow meter well and this kept the light out for a solid month before they gave up and sent me to the dealer when it came on again.

Now the dealer has told me I need both a new Mass Airflow sensor and an new air/fuel ratio sensor.

My question is...I thought I already replace the air/fuel ratio sensor? How many of them (O2 sensors I mean) are there and how can I know that the Mass Airflow actually need to be replaced?

Should I try cleaning the Mass airflow again? and lastly, if I do this, can I reset the check engine light myself to see if it is better? or will it just go out if the situation improves?

Is this Mass Airflow meter something I can replace myself? It looks very straight forward sitting there beside the air cleaner housing.

thanks!

Steve

lakechewbacca · 03-31-2005, 06:48 PM

Mass air flow sensor is easy. Just a couple of clamps. It is very expensive. Cheapest I found was $175 with a $50 core charge.I just blew my engine in my 92 4runner. The meter I bought is only a month old. If toyota won't honor their head gasket recall, I'm gonna junk it. I'd sell you the meter if you want. I'll know by mid-week next week. PM me if you're interested.

***Bakemono*** · 03-31-2005, 07:20 PM

You should have 2 O2 sensors (1 in each exhaust manifold).
The trouble code should tell the mechanic exactly whats going on and they should be able to figure out what part is causing the problem.
Cap'n

steveo64 · 04-01-2005, 01:24 PM

Will the check engine light go out on its own after the parts are replaced? or does it have to be reset?

Will disconnecting the battery reset the check engine indicator?
thanks,

Steve

***Bakemono*** · 04-01-2005, 05:00 PM

Im not sure. On the newer vehicles that light will only go out once you clear the trouble codes with a code reader.
Being that its a '90, the light may go out once the problem stops occuring. I know that the check engine light on my '85 4Runner would come on during warm days. It would come on just before I shifter into 3rd gear and then would go off once I shifted into 3rd.
My '90 4Runner had the check engine light come on once when I replaced the air filter and forgot to reconnect the mass airflow sensor.
So, its possible than the light may go out once you fix whatever is causing the problem.
Cap'n

burger · 04-01-2005, 05:22 PM

unhooking the battery for a couple minutes should clear your codes.

steveo64 · 04-01-2005, 05:28 PM

thanks a bunch for the info!

steveo64 · 04-04-2005, 12:44 PM

Hi there,

I tried to clean the old Mass Airflow sensor and it basically stopped the engine from running.

The good news is that I got a new one from Toyota, $139 and after about 10 minutes driving the Check Engine light is out.

I am hoping it stays out.

So, I believe the computer must do an engine diagnostic periodically to see what is wrong...I know my Chrysler van did that, maybe it is a standard thing.

Ciao...