Benny701

Hey,
I have a 2000 GS400 with 227k mi. Recently, my CEL has been going on and off. I've checked the codes before and after to see if they are the same. They are: PO420 Efficiency Below Threshold and PO171 System too Lean (Bank 1).

I cleaned the MAF sensor, changed both air filters, and the throttle looked fine.

Here's the interesting part; since I've owned it (2nd gen), the fuel level indicator will not drop past 1/8 of a tank without her running out of gas.

I'm considering trying to drop a sparkplug and see if it burns off leftover fuel that's been sitting and check for leaks but, I wanted to ask if anyone thinks differently. Eg replace the O2 sensor first or have experience in knowing it's definitely the cat.

Anything would be helpful. Thanks!

BCP43002

For P0420 look at:
Gas leakage on exhaust system
Heated oxygen sensor

Three-way catalytic converter
for P0171:
Air induction system

Injector blockage

Mass air flow meter

Engine coolant temp. sensor

Fuel pressure

Gas leakage on exhaust system

Open short in heated oxygen sensor (bank 1, 2 sensor 1)
circuit

Heated oxygen sensor (bank 1, 2 sensor 1)

ECM

kevin3344

When mine ran out of gas with 1/4 tank it was the fuel pressure. I would have that checked and see if it helps.

https://www.clublexus.com/forums/gs-...ml#post9484003

Btw, I have a '99 GS4 with 218k.

Benny701

Thank you very much both of you! Keeping this amazing car up can be frustrating because it's solid but, becoming expensive. Upper and lower ball joints "failed" the other day -front driver- and, now, my mechanic (who's the best I've had yet) said the diff was leaking, front sway bar wear and tear, NAPA gave me the wrong caliper after another mechanic did a shotty job on a refurbished pin but did correct the problem (very thankful they stepped up), and ABS sensor is out for the count after the ball joints broke. I'm nearing my wits end. Trust me, I wish I could just take it in and have it taken care of with the best parts because it's the best vehicle I've ever drove.

MattGS300

Got the same codes - turned out it was a dirty injector in the #1 cylinder. A few tanks of premium with injector cleaner and all is right with the world again.

Benny701

I did try that...a couple times, to say the least. CEL always, eventually, came back on with same codes. Still working on it.

kevin3344

Hang in there. It can be frustrating when you have a lot of repairs at once, but these cars are worth it! Definitely get the fuel pressure test when you get the chance. The dealer can do it (expensive) or if you have a good indy. Most of the time when it stalls with 1/8-1/4 tank that points to the fuel pump. Let us know what you find out.

tiguy99

In for any updates!