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Corolla. Crank but no start. (DTCs P0171, P0420)

Hi everyone,
Background: I’ve had various DTC codes over the past few years: 0446, 0133, 0441, 0440, 0130, 01300, 0420. Car has 188,000 miles.

I had both O2 sensors, MAF sensor, fuel pump and filter replaced, PCV valve cleaned and a tune and vacuum leak fixed 20K miles ago but was still getting codes, P0130, 0300 and 0420.

In the last couple of weeks I’ve been getting P0171 (too lean Bank 1) which appears about 8 miles after code reset. Additionally a couple of days ago it stalled and only started with starter fluid spray. I found a leak (water spray) where the air intake manifold joins the throttle body and fixed that. Also recently noticed hesitation when accelerating which was getting worse. Car stalled again. Couldnt get started. Started next day then later didn’t start.
Was also getting P0420, 0446 and also 0133 codes in the last couple of weeks.

Any input? Vacuum leak, fuel pump, filter, fuel injectors? Battery seems OK and it ran for several seconds with starter spray so I guess electricals ok?

I have another vehicle so I have time to try and get it at least started on my own.

What year?

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Look for an air leak in the intake or the exhaust on the bank 1 side.

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  1. I forget to include that!

You need to put a scanner on this to read live data. Ask your question at 8th generation forum. Registration is free

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It’s a 2001. ( sorry for the late reply. My new account was on hold)

I think it’s time to get a later model car.

Sounds like the fuel pump has failed. Measure the fuel pressure, check for power to the pump.

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Thanks for your useful replies.
The car started today and I read the live data while idling once warmed up.
They are:

STFTrim (%): between -5 and 2
LTFTrim (%) about 20
MAF (lbs/s): 0.01
LoadPCT (%): about 19.6
TP(%): 10.2
O2B1S1(V): between 0.1 and 0.8
O2B1S2 (V): Between 0.1 and 0.8
SparkADV: Between 11.5 and 14.0

What stands out for me is the long term fuel trim, which in my limited understanding is too high,
Vacuum leak?

Can you post the fuel trims at high rpm/ engine under full load?

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While idling and reving to 3,600 rpm:
Short term was between -8 and 3
Long term was about 26

I didn’t want to drive far but with my foot on the gas and accelerating:
Short term was about 16
Long term was about 34

Increase+ fuel trim at higher RPM indicates MAF or fuel delivery problem.
Can you post the MAF reading during hard acceleration.
It should read around 50-70 g/s. If so then verify fuel pressure as has been suggested.


Thanks. The car was very hesitant to accelerate (seemed OK in reverse) with, at least at first, little response to gas. But when I got it moving with my foot down on the gas the MAF reading got up to about 33 g/s.
I didn’t want to go to far and have the car stall.

The 20+% long term fuel trim means the computer is having to increase the injection of gasoline by 20% above what it thinks it should based on the other sensors, in order to get the fuel air mixture correct at the O2 sensor in the tailpipe. This means some combo of fuel system and air leak problems. Low fuel pressure could cause this. Likewise, air leaking into he engine (like from the brake booster). A third possibility is that air is leaking somewhere between the engine air filter and the throttle body. Suggest to remove all that rubber stuff and inspect it on the bench for problems. You have a known good engine air filter installed, right? There’s a fourth possibility, an exhaust system leak occurring before or near to the O2 sensors. My first guess is a low fuel pressure, so suggest to have the fuel pressure measured. What’s the status of the fuel filter? If it is original to the car, might want to replace it as part of the mix. Has the MAF been cleaned? Given that it won’t even start, I’m still leaning towards low fuel pressure. Most of that other stuff, if it was the problem, wouldn’t likely make it impossible to start. It would just run poorly is all. When you say it won’t start, you mean it cranks ok, but doesn’t catch and run, right?

Thanks for your reply. I mentioned in my initial post that the car stalled and wouldn’t start. This was true for a couple of days. But now it seems to be starting on each attempt. However it is very hesitant to accelerate and idles rough.

The fuel filter, fuel pump, MAF sensor both O2 sensors were replaced about 20,000 miles, two years ago. This is in the original post.

Sounds like it is time for a fuel pressure measurement. That’s usually done idling in the driveway (or shop floor). In your case your shop may have to rig it up so they can measure the fuel pressure while driving.

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