Codes P2177, P0401 and P0137?

KLEENEX TISSUE BOX

MEMBER
2008 MAZDA 3
2.3L
4 CYL
2WD
MANUAL
230,000 MILES

The first code that appeared was P2177.
After a few weeks P0401 showed up.
Prior to both codes the EGR valve was replaced. Vacuum leak test with brake cleaner showed no major leaks. No immediately visible exhaust leaks.
On a cold start, engine typically revs up to 2000 rpm with no gas input

I suspected a dirty intake, clogged EGR pathway, or even messed up MAP sensor. But I haven't looked into it yet.

Few weeks later, P0137 code shows up

Internet says:
P2177: Engine lean off idle
P0401: Insufficient EGR flow
P0137: Heated o2 sensor low voltage

Please advise.

7 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Based on the codes, it sounds like you have a vacuum leak. Have you checked around the EGR to check if the gasket is in good condition? If there is a leak, it could be causing a lean fuel mixture and limiting the amount of flow to the system.

I attached a pic below showing the EGR valve location. Confirm there are no leaks. Additionally, check around the different vacuum hoses for damaged, cracked, or disconnected hoses.

Here is a link that explains how to do it:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Let me know if this helps.

Take care,

Joe

See pic below.

Image (Click to make bigger)

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Wednesday, August 28th, 2024 AT 7:52 PM

KLEENEX TISSUE BOX

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4 POSTS

Hi Mr. Joe,

I inspected the various vacuum hoses. One hose seemed to be not on all the way, so I ensured that it was. No change was made in performance, however.
I also sprayed brake cleaner while the engine was idling around the EGR gasket's location, throttle body gasket, vacuum hoses, and intake manifold. No change in idle speed or performance occurred.

EGR valve removal on this model is a tedious procedure because there is a massive coolant hose blocking one of the bolts. I will observe the gasket once there is a clear diagnosis that points to a leak in that area. I will consult with my teacher who is a certified mechanic to aid me with visual inspections as well.

I also recorded some fuel trim data to provide to you.
On cold start:
Oxygen sensor 2 bank 1 remains between 0.1-0.3V.
Once heated up O2 voltage remains around 0.7V or 0.9V at idle.

Fuel trims at operating temp:
LTFT goes from 12% to 20.31% when any throttle is given
STFT At idle: Between 0% and -3%. At 1500rpm: 3-5%. At 2500rpm: 7-10%. At 3000rpm: 13%

Please advise Mr. Joe

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Sunday, September 1st, 2024 AT 10:03 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The STFT looks perfect, which indicates no lean fuel mixture as indicated by the code. The oxygen sensor readings are also good. The code indicates low voltage, but they are within the normal range.

Have you tried clearing the codes to see if the same ones return?

Joe

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Sunday, September 1st, 2024 AT 8:09 PM

KLEENEX TISSUE BOX

MEMBER
4 POSTS

Hey Mr. Joe,

Today I cleared the codes. After about 10 miles of driving Check Engine Light came on for:
P2177
Here is some freeze frame data for P2177
Stft: 9.375%
Ltft. 20.3125%
Rpm: 2344
MAF air flow rate: 13.85g/sec

Please advise sir.

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Monday, September 2nd, 2024 AT 5:09 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Since that was the first code to return, that is where we need to start. If you look below, I attached the diagnostics specific to the code. Take a look through them and let me know if this is something you are comfortable performing.

Take care,

Joe

See pics below.

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Codes P2177, P0401 and P0137?

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