So, what year are we talking about, how many miles and ditto Nad1370’s question?

P0171 and P0174 codes are fairly numerous and not that difficult to fix for the average DIY’r to accomplish.

P2198 and P2916(?) codes go hand-in-hand and here’s an example of how to start clearing them. A lot of indicators in what I’ve experienced say cleaning the MAF is a good start, and I’ll add... clean the Throttle Body while you’re cleaning the MAF. Please know that MAF’s do go bad, but cleaning them with something like some CRC Throttle Body Cleaner has been known to produce excellent results. While I’m at it, how’s the air intake filter? Basically, your engine is running rich and all sensors downstream of the fuel master mixer, the MAF, are alarming. Your MAF needs cleaning and your Throttle Body “flapper” isn’t sealing and functioning correctly and also should be cleaned. Do that, clear your codes, see what happens and get back with us.

Good luck.

The car has 178k miles. I have cleaned MAF sensor with CRC MAF spray, but only the resistor. The error codes were cleared with OBD device.
in the past I would get P0174 once in a year, but it became very frequent last few weeks. I thought clenaing MAF would help, but it didn’t it seems. I have also pulled the 25A fuse and left it out 20 mins to reset the ECU.

I was thinking of replacing the tank cap and MAF sensor and see if that helps, but wondered if there’s any other thing I should check or is common to fail.

You have lean codes in both banks.
If you had a 174 before and now a 171.
So many things can trigger a lean code.
But most common are a vacuum leak or your AF sensors going out.
Dont worry about the 2196/98 code since the ECU is fattening up the fuel enrichment to compensate for the LEAN code.
Once you get that lean code resolved, those 2 codes should go away.

Time to get your hands somewhat dirty.

AHA! At 170K+ miles, always change the gas cap. Clean the fuel filler seat and yes, replace the cap with a Genuine OEM gas cap. $20 well spent and one of the most neglected parts and I’ll add that it helped fix my own ‘05 ES330 along with cleaning the MAF along with the cleaning the Throttle Body itself. Keep in mind the big problem of junk and crud will be on the backside of the Throttle Body butterfly keeping it from closing properly and screwing with proper air flow through there. Put some silicon spray on the gas cap rubber seal and give it a few clicks to boot. Disconnect Negative pole of battery for 15 - 20 minutes, replace and take it for a drive to burn any cleaner out.

I’ll add that when I cleaned my Throttle Body, I took it off and had it “in hand” to clean, but with a toothbrush and taking your time a good cleanup can be accomplished without removal. Carburetor Cleaner is OK to use because it is “better” at removing gunk, but spray it away with CRC to remove any residue. Carb Cleaner cleans MAFs better, but be sure to spray it down with CRC afterwards to remove Carb Cleaner residue there. Also spray CRC on the electrical connectors to the MAF.

I also recommend a Clublexus favorite here, a bottle of Gumout Regane High Mileage Fuel System Cleaner into a tank of Hi-Test gas for the finale.

While I’m ranting and hoping I won’t be accused of “throwing parts and money”, a Genuine OEM PCV valve replacement is about $10 (DIY and easy to do) is worth thinking about if you have the volition to do so. They’re another of those “neglected parts” that few think about.

Happy trails and let us know how it goes.

The tank cap was replaced two days ago, and it didn’t quite help. It does take a bit more time for the codes to pop out so it probably helps a bit after all, not sure.
I was about to order a new MAF sensor and see if that would have helped, but today I got six codes. Four already mentioned, and P0137 and P0157 O2 sensor circuit voltage too low.

Are these also reflecting possible MAF sensor issue or I should replace O2 sensor as well?

So what you’re getting now is that both banks are showing the same problem and them both going bad at the same time is a sign that your real problem is still something “common” to your same previous codes as well as the new ones. IOW, I’d suggest at this point to wait until MAF is changed before moving along.

Here are the symptoms of your O2 Sensors going bad.

• Faulty Rear Heated Oxygen Sensor Bank 1&2
• Rear Heated Oxygen Sensor Bank 1&2 harness is open or shorted
• Rear Heated Oxygen Sensor Bank 1&2 circuit poor electrical connection
• Inappropriate fuel pressure
• Faulty fuel injectors
• Intake air leaks may be faulty
• Exhaust gas leaks

Like I said, the probabilities of both sensors going bad plus the other codes together is unlikely. Both sensors’ separate harnesses and electrical connections going bad plus the other codes together is unlikely. Your fuel injectors affecting both banks going bad together is unlikely. Exhaust gas leaks? Nah. Air intakes faulty? Considering the other codes along with the new ones? Maybe at best.

A Genuine OEM MAF is expensive and it “encourages” many buyers to go to an aftermarket device, but don’t be that guy.

Good luck and get back with us. ��

Amazon

Amazon

This does change things a bit knowing the AF Sensors didn’t go bad simultaneously, but getting the MAF and Throttle Body getting cleaned while sorting this out will help. P0171/0174 doesn’t mean they’re bad, it means the ECM has detected a big problem.

To keep the engine running properly, the Engine Control Module measures the oxygen content in the exhaust with oxygen sensors and makes adjustments to the mixture by injecting more or less fuel.

The control module operates within specific parameters and under normal conditions, it will make minor adjustments to the air/fuel mixture. When these adjustments become too large, a fault code is set. When the P0171/P0174 code sets, the oxygen sensors are detecting too little oxygen in the exhaust and the control module is adding more fuel than normal to sustain the proper air/fuel mixture.

When a vehicle has the fault code P0171 and or P0174, it means that computer can no longer automatically adjust the mixture between air and fuel. Code P0171 applies to Bank 1 and P0174 applies to Bank 2.

When the code says that the Fuel System is "too lean," it means that the computer has been adding more and more fuel, which is called Long Term Fuel Trim. Ideally, the Long Term Fuel Trim should be close to 1 to 2 percent. When a code P0171 is set, it means that the Fuel Trim is anywhere from 15 percent to as high as 35 percent compensated. When this happens, the computer knows that there is an improper condition in the control of the Fuel System.

Common Problems That Trigger the P0171 and P0174 Code

PCM software needs to be updated
Vacuum leaks (Intake Manifold Gaskets, vacuum hoses, PCV hoses, etc.)
Mass Airflow Sensor (MAF)
Plugged Fuel Filter or weak Fuel Pump
Plugged or dirty Fuel Injectors

Cheers

As the codes progress downstream from the MAF, the pairings of bank Sensor problems that are happening is “normal”. You have to start clearing codes by earliest occurrence and the latter problems now being experienced may just clear out with a reset.

The MAF is a very important and critical component of how well your engine runs and since it’s the furthest upstream, outside of the intake air filter which I’ll also address, from the engine sensors alarming... Start there and work downstream.

This car has 178K on it and cleaning the MAF has worked before, a time or two. So the MAF is clean. What about the Intake Air Filter? If the MAF works off temp and wind to signal the ECM how much gas to provide, then consider at least a peak at it in the name of “getting it right” this time and change it out. DO NOT consider K&B conversions. Oil based filters have been proven to cause problems with MAFs because of the oil on the sensor stem. To make things worse, most K&B users use more or improperly apply the oil after cleanings. Efficient Air Intake Filter/Fuel Systems were designed by engineers and sometimes defying their wisdom has it’s consequences.

The next item downstream that demands attention but seldom gets recognized is the Throttle Body. It MUST be clean and free of the sticky goo that collects mostly on the backside of the butterfly that keeps it from closing/opening on demand and the entire designed airflow pattern has been changed as well. I’ll advise going to the trouble of reading up and learning how to remove the Throttle Body so that a thorough cleaning of it can be accomplished. There are DIY videos all over the internet and many here at clublexus have them tabbed for anyone that asks. If the average person would take care these three components, many of the downstream codes alarming would be from actual sensor failure (age, heat, design) instead of what we witness otherwise.

If your interested, here’s an excellent article about MAFs and their function.... Easy reading.

https://www.samarins.com/glossary/airflow_sensor.html