Hi

For the past few weeks the CEL will come on and the go off usually within a few hours of coming on. Code shows P0171 "System too lean" anyone know what would cause that error to be intermittent?

From what I've read it can be caused by any number of issues like. O2 sensor, MAF, or leaky tubes. Anyway to narrow it down before paying for a mechanic?


If it was the 02 sensor wouldn't it be permanent, and have more then 1 fault code? Anyway to rule out the O2 sensor just using a OBD II scanner?

At idle with the car in park the short and long term fuel trims stay in single digits. When I start driving they can go upto 30%

 

Check your vacuum lines first. That's the easiest thing to check- and the cheapest to fix.

 

Yes, check all the vacuum lines, anywhere you can find them. Hardened from heat & age? Brittle & beginning to crack?

However, the scenario seems backwards. At idle is when the vacuum is strongest, so that's when you'd expect it to lean out.

 

How many vacuum lines are there?
So you're saying the fuel trim should be highest when idleing?

 

I guess I should have said anything that might be a vacuum leak.

Hose from the PCV valve to the manifold.
Hose from the brake booster.

Then there's gaskets where the intake manifold bolts together. And the throttle body bolted to the manifold.

As far as the fuel trim, not sure I'm thinking it through correctly... Idle is when the air flow is lowest, and the vacuum is strongest. So any vacuum leak becomes larger just as the "intended" air flow becomes smaller. Have to add a larger percentage of extra fuel to keep the O2 sensors happy.

 

Clearly it's just me, but the whole "V4" name in the title of this thread is driving me crazy. Splitting a hair here, if you have a 2001 Accord you either have a V6 or an I4 engine. Now back to our regularly schedule discussion.

 

I couldn't find any crack in any of the lines from my quick look.

The Intake manifold pressure at idle is 3.9 psi. Would that change if the vacume lines were leaking?

One thing seemed weird to be. O2 voltage bank 1 sensor 1 stayed around .75v while bank 1 sensor 2 kept fluctuating between .2 and .8v. Is that normal?

 

I thought I was the only one with that problem.

 

Are you measuring B1S1 with a scanner or volt meter?

If your accord has an a/f sensor, then the output is different for that type of sensor. Look up the OEM part number on a site like hondapartsnow.com and post it on here. You don't want to replace a properly working sensor.

 

Here is a log of 2 minutes of data hope it helps.

https://drive.google.com/file/d/1pBC...bQiKH4Q3E/view

I believe this is the part.

https://www.hondapartsnow.com/genuin...fold,3058068,6