Bank specific codes caused by sensors common to both banks

Maintenance/Repairs
1

I have a question about diagnosing bank specific codes. Such as P0172: Bank 1 too rich.

Some may say that a possible cause of this is the mass air flow sensor. But wouldn’t this also throw a P0175 Bank 2 too rich as well?

2

Any of the following can cause such a code.

A dirty mass air flow sensor overstating the amount of air entering the engine which may cause excessive fuel delivery
A bad oxygen sensor
A leaking fuel injector allowing too much fuel to enter the combustion chamber
A faulty fuel regulator, which may not be regulating the pressure of the going to the engine as it should
A vacuum leak
A possible fault in the coolant system such as a stuck thermostat or bad coolant temperature sensor
Worn spark plugs

Tester

3

Why would this cause a P0172 code and not P0175?

4

It probably would also cause a P0175 DTC.

Tester

5

You need to look at live data and freeze frame data

Even though you “only” have P0172, it’s possible the bank 2 fuel trims aren’t that great, perhaps just below the threshold for setting a code

The fault code is only a starting point for your diagnosis

So . . . just because you don’t have a particular fault code doesn’t mean everything is great

4 Likes
6

Consider Tester’s list of potential causes for a P0172…

  • A dirty mass air flow sensor overstating the amount of air entering the engine which may cause excessive fuel delivery
  • A bad oxygen sensor
  • A leaking fuel injector allowing too much fuel to enter the combustion chamber
  • A faulty fuel regulator, which may not be regulating the pressure of the going to the engine as it should
  • A vacuum leak
  • A possible fault in the coolant system such as a stuck thermostat or bad coolant temperature sensor
  • Worn spark plugs

Not having a P0175 is a hint for what could be wrong.

Which one of these cause could cause the P0172 on ONE bank only? A bad O2 sensor (on bank 1) a leaking fuel injector, worn spark plugs or even a vacuum leak very close to bank 1.

Codes don’t tell you what’s wrong, they are only reporting the error, not the cause.

2 Likes
7

I concur w/OP, maf problem would likely cause both banks too rich, not just bank 1. First priority, I’d be looking for something that would only affect bank 1. This presumes the engine has two exhaust banks, each with their own oxygen sensors of course.

8

Notice the OP hasn’t even told what car this is…

9

My first priority would be looking at freeze frame data . . . what were the fuel trims on both banks when the code set?

My second priority would be looking at live data . . . what are the current fuel trims on both banks?

That should take only a few minutes to get the answers to both of those questions

Then you can proceed to do more testing

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