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2019 CT6 3.6L Excessive Oil Consumption and P0420/P0430 Codes

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Mike T. · rep 0 · May 25, 2:50 AM · 1 replies · solved · Question

Vehicle: 2019 Cadillac CT6 3.6L Luxury

I'm experiencing significant oil consumption in my 2019 Cadillac CT6 with the 3.6L V6 engine. I'm having to add a quart of oil every 1,000 to 1,500 miles, which seems excessive for a car with only 60,000 miles on it. There are no visible leaks under the car.

Recently, the check engine light came on, and I scanned it to find P0420 (Catalyst System Efficiency Below Threshold Bank 1) and P0430 (Catalyst System Efficiency Below Threshold Bank 2). I suspect these might be related to the oil burning issue.

Has anyone else with a CT6 or a similar 3.6L engine experienced this level of oil consumption, and did it lead to catalytic converter issues? What were the solutions, and how costly were the repairs?

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 25, 2:50 AM

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ClearTheCode admin answer:

Your 2019 Cadillac CT6 3.6L experiencing excessive oil consumption coupled with P0420 and P0430 (catalytic converter efficiency codes) is a strong indication that the two issues are directly related. When an engine burns oil, the oil byproducts can contaminate and damage the catalytic converters, reducing their efficiency and triggering these codes.

Here are the common causes for oil consumption in the 3.6L engine and how it impacts the catalytic converters:

Causes of Oil Consumption:

  1. PCV System Issues: A faulty Positive Crankcase Ventilation (PCV) valve or a clogged PCV system can lead to excessive crankcase pressure, forcing oil past piston rings or valve seals. This is a common culprit.
  2. Worn Piston Rings: Over time, piston rings can wear, allowing oil to bypass them and enter the combustion chamber to be burned. This is a more serious and costly repair.
  3. Worn Valve Stem Seals: The seals around the valve stems can harden or wear out, allowing oil to leak down into the combustion chamber, especially during deceleration.
  4. Turbocharger Seal Leaks (if applicable): If your specific 3.6L has turbochargers (some CT6 models do), leaking turbo seals can cause oil to enter the intake or exhaust side.

Impact on Catalytic Converters:

  • When oil is burned, it produces ash and uncombusted hydrocarbons that coat the ceramic matrix of the catalytic converter. This coating reduces the converter's ability to store oxygen and convert harmful emissions, leading to the P0420/P0430 codes.

Repair Steps (General):

  1. Diagnose Oil Consumption: A technician will perform an oil consumption test to confirm the rate. They will also inspect the PCV system and may perform a compression or leak-down test to assess piston ring and valve seal integrity.
  2. Address Oil Consumption Root Cause: Depending on the diagnosis, this could range from replacing a PCV valve to more extensive engine work like replacing piston rings or valve stem seals.
  3. Catalytic Converter Replacement: Once the oil consumption issue is resolved, the catalytic converters will likely need replacement, as they are often permanently damaged by oil fouling.

When to see a shop:

  • Promptly. While the car may still drive, excessive oil consumption can lead to engine damage over time. More immediately, the P0420/P0430 codes indicate that your emission control system is not functioning correctly, which can lead to failed emissions tests and further damage to other components if ignored. A qualified shop can accurately diagnose both the oil consumption source and the catalytic converter health.
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