Check Engine Light

[4-Ruiner]

My check engine light came on last week. I took it to my mechanic and we scanned the code. It came up "Lean Bank 171."

So basically I am not delivering enough fuel, right? Rather that just starting to replace O2 sensonrs and other expensive parts, he told me to just go ahead and drive it until I notice a loss in power or something strange. He reset the code, and I drove for almost a week until the light came on again.

What should I do, guys? Any advice would be helpful. If it's not the O2 sensors could it be the fuel pump or fuel filter? What else could it be?

 

[greasefingers]

An Intake manifold leak would produce a lean mixture. This is because the MAF sensor measures the grams/second across MAF, but cannot know how much additional air is being introduced somewhere else.

Five to six years is all one can expect from early model year oxygen sensors. I do not know about late model years. It is a main part of the emissions system and is covered under a warrantee. If you have the Owners manual, then look into this.

The O2 sensor is itself is very hard to check. The output plotted over time is a sinewave. The voltage fluctuates from around 0.1 to 0.9 volts. So a multimeter will almost be useless. It will tell you if the heater circuit of the sensor is receiving power and a resistance check would tell you if the heater is Shorted or Open.

 

[bsackamano]

I also had fuel lean CELs on my '99 around 100K miles. The dealer replaced the MAF sensor. It still hesitated but the light went out for 2-3 months until it started reporting misfires on 3 cylinders. After some research I think the problem was clogged injectors all along. If the fuel is not atomized properly it will not burn completely and oxygen will be left over. When this goes through the exhaust, the O2 sensor sees it and assumes not enough fuel is being injected or that it is running lean. This doesn't explain why I was only getting lean codes on one bank as you are, but I still think that is my problem. I'll find out for sure later this week when I have an injector service. Anyway, watch for hesitation, dropping fuel mileage, and misfire codes.

 

[4-Ruiner]

Well, the light went off mysteriously the other day...so I am just gonna go ahead and drive it for a while. I do not notice any hesitation or loss in power.

 

[Ltd4Runner4x4]

I just recently had the same problem--check engine light came on and the diagnostic reading said that the mixture was too lean. I tried changing the upstream O2 sensor, but the light just came back on. I took it to the dealer and they did a quick diagnostic check and it ended up being the mass air flow sensor. I got the part from a dealer in TX online for about $110 and it took 10 mins to replace it---problem fixed.

 

[NCSCOTT]

I just recently had the same problem--check engine light came on and the diagnostic reading said that the mixture was too lean. I tried changing the upstream O2 sensor, but the light just came back on. I took it to the dealer and they did a quick diagnostic check and it ended up being the mass air flow sensor. I got the part from a dealer in TX online for about $110 and it took 10 mins to replace it---problem fixed.

I do not mean to thread jack here. But Nice to see another Raleigh member.

 

[Spider5]

Check the fuel filter or fuel pump as possible problems. A very clogged up fuel filter gave me this code before on an old Tercel. Most likely however, it is the MAF.

 

[mikes4runner]

Hold on the first thing you should do is to clean the MAF with some carb cleaner then reset you ECU to clear the code. easy and a comman thing on newer cars/trucks. before you start replacing the MAF or O2 sensors. I am surprised the mechanic did not do this

it is routine maintence on my MR2 Spyder



MIke

 

[Spider5]

Hold on the first thing you should do is to clean the MAF with some carb cleaner then reset you ECU to clear the code. easy and a comman thing on newer cars/trucks. before you start replacing the MAF or O2 sensors. I am surprised the mechanic did not do this

it is routine maintence on my MR2 Spyder



MIke

:iagree:

A dirty MAF is very common with this problem especially if you added an oil based air filter. But, unfortunately, a bend MAF plate it also quite common, and when this happens replacement is best.