P0174 on Buick: How to Diagnose & Fix
System Too Lean (Bank 2)
2 Buick models · 2 documented issues · 2 critical · $400-$1,200 repair
P0174 on Buick by model: symptoms, diagnosis and fix
The 3800 Series II (and early III) V6 in Park Avenue, LeSabre, Riviera, Regal, Lucerne — and shared Pontiac Bonneville/Grand Prix, Olds 88/LSS, Chevy Monte Carlo/Impala — suffers infamous lower intake manifold gasket failure. Plastic intake material softens under coolant exposure (especially Dex-Cool); gasket erodes and leaks coolant into the lifter valley, mixing with oil. Catastrophic if undetected.
Common Symptoms
- coolant loss with no external leak
- milky oil
- overheating
- sweet smell from exhaust
- rough idle
How to Fix
Replace LIM gasket with updated Fel-Pro MS98003T (improved metal-reinforced design) — $400-$800 at independent. Replace upper intake plenum at the same time if cracked. Drain Dex-Cool and refill with Zerex G-05 or compatible HOAT. Inspect oil for coolant contamination at every change; milky oil means immediate teardown.
Sources for this issue (1)
Same 3800 V6 LIM-gasket failure mode as Park Avenue — extremely widespread in 1995-2005 LeSabres. Coolant migrates past degraded plastic-and-rubber gasket into the valley, contaminating engine oil. Owners commonly first notice low coolant with no visible leak; by the time milky oil appears, bearings may already be damaged.
Common Symptoms
- coolant loss
- milky oil
- overheating
- sweet exhaust smell
- rough idle
How to Fix
LIM gasket job is the same: Fel-Pro MS98003T or similar updated design — $400-$800. Replace UIM plenum if cracked, and drain Dex-Cool. Many shops will replace the EGR stovepipe gasket and throttle body gasket while everything is apart.
Sources for this issue (1)
P0174 code reference
General diagnostic-code context. The code alone does not confirm a cause for your vehicle; use the applicable issue card and its sources.
Frequently asked questions
What does P0174 mean on a Buick?
P0174 stands for "System Too Lean (Bank 2)." P0174 means the engine computer detected that the air-fuel mixture on Bank 2 (the side of the engine with cylinder 2) is running too lean — too much air relative to fuel. The computer monitors this through the oxygen/air-fuel sensors and fuel trims; when it has to add a large amount of extra fuel to compensate and still can't reach the target, it flags the mixture as too lean. A lean condition can cause rough idle, hesitation, or misfires, and over time can raise combustion temperatures. Because it's Bank 2 specific, an unmetered air leak on that bank or a fuel delivery shortfall is typical. On Buick it is documented across 2 models: Park Avenue, LeSabre.
What are the most common causes of P0174?
The most common causes of P0174 are: Vacuum or intake air leak (hoses, gaskets, PCV), Dirty or failing mass airflow (MAF) sensor, Weak fuel pump or restricted fuel filter (low fuel pressure), Clogged or underperforming fuel injectors, Leaking intake manifold or throttle body gasket, Faulty or contaminated oxygen / air-fuel sensor, Exhaust leak upstream of the oxygen sensor, Stuck-open EGR valve. The specific cause varies by vehicle.
How much does it cost to fix P0174 on a Buick?
Published repair estimates on Buick range from $400 to $1,200 depending on the model and root cause. If an issue mentions a recall or campaign, check your VIN with the manufacturer or NHTSA and confirm eligibility and coverage with a dealer.
Looking for P0174 on a different make?
View P0174 across all makes →Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.