A 2013 Cadillac ATS arrived with a check engine light and a scanner showing P0171, P0299, P06DE, P2270, and P2097. Seeing lean codes mixed with a turbo underboost and an oil pressure control circuit fault usually means someone is about to spend a long time checking wiring. I see this exact combination in the diagnostic platform we build, and it perfectly illustrates why treating codes in isolation leads to wasted time.
Here is how our own data breaks down the root causes for this specific vehicle and code cluster.
The link between lean conditions and underboost
The engine in this vehicle is the 2.0L LTG Turbo. When codes P0171 (System Too Lean), P2270 (O2 Sensor Signal Stuck Lean), and P0299 (Underboost) appear together, our platform ranks a PCV system failure or intake vacuum leak as the most likely culprit at 90 percent probability.
These engines are highly prone to vacuum leaks from brittle plastic PCV hoses, intake manifold components, or the valve cover diaphragm. Constant heat cycles bake the plastic until it cracks, allowing unmetered air into the engine. That unmetered air triggers the lean condition for P0171 and forces the downstream oxygen sensor to report a consistently lean state for P2270. It also disrupts the Mass Airflow sensor readings, which leads to incorrect boost calculations and the P0299 underboost code.
The fix often involves replacing the PCV hose assembly (OEM parts 12673868 or 12681589) or addressing leaks from the active motor mount vacuum line under the intake manifold. This matches the known issues in TSB PI0940A for 2013 to 2015 ATS 2.0L and 2.5L models. The recommended diagnostic steps are straightforward. Visually inspect the hoses, listen for hissing at idle, smoke test the intake system, and monitor your Short-Term and Long-Term Fuel Trims.
The Mass Airflow sensor factor
Ranked next at 70 percent probability is a dirty or faulty Mass Airflow sensor. If the sensor is contaminated with oil or debris, it under-reports the actual volume of air entering the engine. The Powertrain Control Module then commands too little fuel, resulting in the P0171 lean code.
A faulty MAF sensor also indirectly affects the turbocharger performance and boost pressure calculations, contributing to the P0299 code. Cleaning the MAF sensor (ACDelco 213-4693 is common here) is an inexpensive diagnostic step. Monitor the MAF readings with a scan tool, and try unplugging it as a diagnostic test to see if the engine behavior changes.
The isolated oil pressure fault
Code P06DE stands out from the rest. It specifically indicates an issue with the engine oil pressure control circuit. On the LTG engine, this means the Engine Control Module cannot effectively control the variable displacement oil pump.
Our system ranks this cause at 60 percent probability, and it is generally completely unrelated to the intake and fuel system faults. The failure points are typically the oil pump solenoid itself or its wiring harness. The wiring harness can suffer from oil intrusion or heat damage. That damage can travel through the wire insulation and eventually affect the ECM connector. To test this, you need to measure the mechanical oil pressure, thoroughly inspect the oil pump solenoid wiring harness, and monitor the solenoid duty cycle with your scan tool.
Direct turbocharger system leaks
If the intake vacuum and MAF check out, we look at direct turbocharger system boost leaks or a diverter valve failure, ranked at 50 percent probability. P0299 can be caused by leaks within the charge air system, specifically the charge air cooler pipes, intercooler, and their connections.
The turbocharger diverter valve on the compressor housing can also fail due to a torn diaphragm, or it can become stuck open, preventing the turbo from building adequate boost pressure. The correct approach here is to smoke test the charge air system, visually inspect the pipes and diverter valve, check the wastegate actuator rod for binding, and monitor the requested versus actual boost pressure.
Do you see this cluster of codes often on the 2.0L LTG, and do you tackle the vacuum leaks or the oil pressure circuit first?