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Heater blows cold on passenger side AND p0171 bank 1 code. Related?

I have two issues on my 1998 Buick LeSabre Limited.

  1. Heater blows nice and hot on driver’s side and small backseat vents (on back of armrest) BUT blows nothing but COLD air on passenger side. This is true upper, middle, lower vents.

  2. The check engine light just recently popped a p0171 code, bank 1.

Is there any chance these are related (vacuum leak)? If anyone has any ideas for fixing either/or, I would appreciate any guidance.

That means Bank 1 is running lean. Some sort of injector problem or leak on intake system, perhaps. Should not affect heating system.

Does the engine get hot like normal?

They could be related if the controls for the heater/AC system are vacuum controlled rather than electrical actuators as is more common in newer cars. If you don’t know how it works. ask at a dealership, or you might could figure it out by just taking a look at the car’s firewall area. Do you see any vacuum lines going through the firewall, near where heater/AC flap doors would be located inside the passenger compartment? If so, those are probably the power sources to move the heater system’s vent doors back and forth. You could temporarily block off those vacuum lines before they go though the fire wall and see if the lean code went away. If it did you’d be pretty sure there’s a leak in one of the lines under the dash somewhere.

More than likely the no heat problem on the passenger side is due a faulty passenger side blend door actuator.

These engines are well known for developing intake manifold leaks. So the P0171 code might be caused by a leaking intake manifold.


I will check all this out. Thanks much. How can I check to see if the Buick
does have intake manifold leaks? And if so, might you know of a good thread
or video or link showing how to repair/replace? I should note – the car
only has 43,000 miles on it. Bought it cheap from a kid who inherited it
from his great-grandparents and it wasn’t cool enough for him.

Get the engine up to operating temperature.

The O2 sensors don’t detect for a lean condition until the computer is in the closed loop mode.

While the engine is idling, take an aerosol can of throttle body/carb cleaner and spray it around the intake manifolds.

If the engine idle speed changes, you’ve found an intake leak.


On this vehicle, there is one upstream oxygen sensor and one downstream sensor. P0171 on a 1998 means lean exhaust. There is no way for it to determine if it’s bank one or two.

UPDATE: I really think the heater issue is related to bad
blend door actuator,
and will be working on it this weekend.

However, the p0171 code has been coming and going. Currently, it is not
showing at all. I do plan to run some tests this weekend to see if I can
pin down what it might be.