P0174 on Cadillac
System Too Lean (Bank 2)
P0174 on Cadillac vehicles indicates system too lean (bank 2). Au7o has documented this code across 4 Cadillac models — most commonly on Allante, DeVille, DTS. 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. Typical repair costs on Cadillac range from $50 to $6,000, depending on the specific model and root cause.
Common Causes of P0174
- •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
P0174 on Cadillac by Model
Cadillac Allante(1 issue)
- 4.6L Northstar V8 Head Gasket Failure (1993)1993
The 1993 Allante was one of the first vehicles to receive the Northstar V8. Early Northstars are notorious for head bolt thread pull-out from the aluminum block, causing head gasket failure. The fix requires Timesert or similar thread repair.
Cadillac DeVille(2 issues)
- Northstar V8 Excessive Oil Consumption1994-2005
Northstar 4.6L engines are known for consuming significant amounts of oil, often 1 quart per 1,000-2,000 miles. The root causes include worn piston rings, valve stem seal degradation, and the PCV system design. The Northstar was designed with tight tolerances and low-tension piston rings for efficiency, which contributes to oil consumption as the engine ages. High oil consumption is so common on Northstars that GM considered up to 1 quart per 2,000 miles "acceptable." This affects all Northstar-powered vehicles (DeVille, DTS, Seville, Eldorado).
- Northstar 4.6L V8 Head Bolt/Head Gasket Failure1994-2005
The Cadillac Northstar 4.6L V8 is infamous for head gasket failure caused by the head bolts pulling out of the aluminum engine block. The original design used steel bolts threaded directly into the aluminum block without inserts, and the threads strip over time from heat cycling. This causes coolant to enter the cylinders and exhaust gases to enter the cooling system. The issue typically occurs between 100,000-150,000 miles but can happen earlier. This is one of the most well-known engine failures in automotive history and affects every Northstar-powered Cadillac (DeVille, DTS, Seville, Eldorado). The repair requires engine removal and Time-Sert or Norm's head stud installation.
Cadillac DTS(1 issue)
- Northstar 4.6L V8 Head Bolt/Head Gasket Failure2006-2011
The 2006-2011 DTS (DeVille's successor) continues to use the Northstar 4.6L V8 with the same head bolt thread-stripping issue. GM made minor improvements to the later Northstar engines (L37 and LD8 variants) but never fully resolved the fundamental design flaw of steel bolts in aluminum threads. The DTS Northstar is slightly improved over the DeVille era but still fails at 100,000-150,000+ miles. Same symptoms, same repair as the DeVille.
Cadillac Eldorado(1 issue)
- Northstar 4.6L V8 Head Bolt/Head Gasket Failure1993-2002
The 1993-2002 Eldorado was one of the first vehicles to receive the Northstar 4.6L V8 and has the same head bolt/head gasket failure. Early Northstar engines (1993-1995) are particularly prone as the design was less refined. The Eldorado ETC (Touring Coupe) uses the high-output 300hp Northstar. Same failure mechanism and repair as all Northstar-powered Cadillacs.
Looking for P0174 on a different make?
View P0174 across all makes →Frequently Asked Questions
What does P0174 mean on Cadillac?▼
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 Cadillac specifically, this code is documented across 4 models.
What causes P0174 on Cadillac vehicles?▼
Common causes on Cadillac: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix P0174 on a Cadillac?▼
Repair costs on Cadillac range from $50 to $6,000, depending on the specific model and root cause.
Which Cadillac models have P0174 documented?▼
Au7o has documented P0174 on 4 Cadillac models: Allante, DeVille, DTS, Eldorado.