how can a straight six have 2 banks?

[chrisjm91]

I have a straight six here with a PO171 lean on bank 1 & PO174 lean on bank 2, and cylinder 4 misfire. I thought only "V" type engines had banks? I raise the rpms and long term fuel trim goes up with it And sitting at idle in parks its reading a 30% load.

[bskeels]

Typically the bank 1 is the upstream oxygen sensor (before convertor) and the bank 2 is down stream (after convertor), codes for the "V" type engines will state "bank 1 sensor 1 or 2" for upstream and "bank 2 sensor 1 or 2" for a downstream code

[Ozark Lee]

That 6th cylinder could be a problem since your sig indicates an 850 T5.



...Lee

[erikv11]

What car is this for?

[jimmy57]

When the engine has two or more front (upstream) catalysts and fuel trim has to be controlled for the groups of cylinders feeding each catalyst, the cylinder groups are known as Bank 1, bank 2, bank 3, etc.
The naming was originally used for V8 and V6 engines where the exhaust manifolds for each side, or bank, had its own oxygen sensor and fuel trim was controlled bank by bank so the catalyst on each side would work best. For in line 6 cylinders it is very common. Cylinders 1,2, and 3 are bank 1 and cylinders 4, 5, and 6 are bank 2. Volvo 6 cylinders from '99 are this way.
Some V12's are 4 banks due to using two separate 6 cylinder engine control modules and 4 upstream catalysts.

[misha]

That 6th cylinder could be a problem since your sig indicates an 850 T5.



...Lee

[chrisjm91]

Thanks for clearing this up for me. Like I said, I thought banks were "sides" of the engine for "V" type engines. But with a straight engine like a straight 6, using 1-3 as bank 1 and 4-6 as bank 2 makes sense.