I have two issues on my 1998 LeSabre Limited.

1) Heater blows nice and hot on driver'* 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.

Likely not. Temperature mix is electronically actuated. Do you have dualzone climate control?

I am not 100% certain, but I think the HVAC mix doors on your car are vacuum activated. There should be a vacuum manifold located behind the glove box with several different colored vacuum tubes branching off of it. Your HVAC issue and the vacuum leak code could be directly related.


Do you have automatic temperature control, or manual?

Thanks. I'll research and let you know. Also important to note -- this Buick has only 43,000 miles on it. Bought it cheap from a guy who inherited it from great grandparents so it'* not gotten much mileage. I do think some of the hoses, etc., could be wearing out, but engine, etc., should be fine.

One more thing -- it is automatic temp control. Has a feature so passenger can control their side, independently.

From what I recall of the automatic system, the air diverters are vacuum actuated, but the temperature mix is electronic, with the actuators a known problem area for cracking internal plastic gears.

I do think a complete inventory and service of failing vacuum lines would be in order, especially the rubber ones.

The plastic ones are probably fine until someone looks at them wrong, at which point they shatter in to a zillion tiny pieces.

For what it'* worth, the ATC system on the 98 LeSabre has a self diagnostic system that might shed some light on your problem. Press & hold the OFF, AUTO, and RECIRC buttons for 1 second, after which the DTC'* will display for 2 seconds each and then return to normal operation. The DTC'* are 2 digit numbers, and I am sure we can find a chart somewhere to interpret them. If you go into diagnostic mode and all that happens is the temperature flashes, there are no trouble codes set in the system.


I still think you are looking for a vacuum leak behind the glove box, but it also could be a broken plastic gear in the blend door actuator (very common on your vehicle).

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.

FYI, I tried this but nothing happened: "Press & hold the OFF, AUTO, and RECIRC buttons for 1 second, after which the DTC'* will display for 2 seconds each and then return to normal operation."

I had a problem with my 1997 Olds 88 not sending the air where I selected and a P0171 code as well. The air would always default to the defroster. I found the vacuum hose that goes to my HVAC was split wide open due to age. It was under the plastic cover at the firewall on the passenger side. I found it by following the hose that tees off of the big hose for the brake booster. Now my HVAC works as it should and no more P0171 code which was caused by that vacuum leak of the split hose....with cars this old you should keep some new vacuum tubing with you.

Did you find the problem?