Fix P0299: Mechanic’s solutions that WORKED

Code Code P0299: Turbocharger/Supercharger “A” Underboost Condition indicates that the turbocharger or supercharger is not providing the expected boost pressure to the engine. This can result from various issues, including a faulty turbocharger, sensor problems, air or exhaust leaks, or software-related issues.

P0299 quick overview

Meaning	Code P0299: Turbocharger/Supercharger “A” Underboost Condition
Is it serious?	Yes, it can affect engine performance and fuel efficiency.
Possible causes	– Faulty or worn turbocharger – Boost pressure sensor malfunction – Intercooler leaks or blockages – Intake air leaks – Exhaust restrictions – Wastegate issues – PCM/ECU software update needed
How to diagnose?	Check for Fault Codes: Use a diagnostic scanner to retrieve and document fault codes. Inspect Turbocharger: Examine the turbocharger for wear, damage, or signs of malfunction. Test Boost Pressure Sensor: Verify the operation of the boost pressure sensor. Inspect Intercooler: Check for leaks or blockages in the intercooler. Examine Intake System: Inspect the intake system for air leaks. Check Exhaust System: Look for exhaust restrictions or obstructions. Inspect Wastegate: Ensure the wastegate is functioning properly. Software Update: Consider updating the PCM/ECU software if recommended. Test Drive: Take the vehicle for a test drive to assess performance and check if the code returns.

Code P0299 indicates that the turbocharger or supercharger is not providing the expected boost pressure to the engine. This can result from various issues, including a faulty turbocharger, sensor problems, air or exhaust leaks, or software-related issues. It’s essential to diagnose and address the root cause to prevent engine performance issues and improve fuel efficiency.

How to fix P0299 – learn from mechanics

I looked into P0299 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Ford

Vehicle Information:

• Make: 2005 Ford
• Model: F-250 Super Duty XLT
• Year: 2005
• Engine: 6.0L

Issue + Repair History:
The vehicle experienced the following issues:

• MIL (Check Engine Light) coming on every 150 miles with P0299 code.
• Previously had P2287 (ICP fault) and P0400 (EGR flow) codes.
• Repairs included replacing the ICP sensor and wiring pigtail for P2287.
• Cleaning the EGR system and EGR valve for P0400.
• Replacing the EGR valve again for sticking.
• Disassembling and cleaning turbo vanes.

Other OBD2 Codes + Test Results:

• No other OBD2 codes mentioned.

What People Suggest to Fix Issue:
Community suggestions included:

• Checking the cam pivot hole in the unison ring for wear.
• Inspecting the intake and exhaust system for leaks.
• Ensuring the PCM has the latest calibration.
• Checking EBP, MAP, and BARO psi readings.
• Verifying that the intercooler is not plugged.
• Checking for aftermarket programmers.
• Replacing the VGT actuator.
• Checking for binding in the turbo linkage.
• Inspecting the condition of the unison ring and center housing for rust or damage.
• Looking for exhaust leaks causing the P0299 code.

Final Fix:
The final fix involved:

• Disassembling the turbo again.
• Finding a notch in the unison ring.
• Replacing the entire assembly with a remanufactured unit, including the center housing and unison ring.
• No MIL (Check Engine Light) issues reported after the replacement.

Case #2: Audi

Vehicle Information:

• Make: 2008 Audi
• Model: A3
• Engine: 2.0L

Issue + Repair History:
The vehicle had the following issue:

• MIL (Check Engine Light) with Code P0299 (Boost Pressure Regulation).
• A P1602 code (Power Supply B + Terminal 30) was also present.

Other OBD2 Codes + Test Results:

• P0299: Boost Pressure Regulation Control Range
• P1602: Power Supply B + Terminal 30

What People Suggest to Fix Issue:
Community suggestions included:

• Checking for common issues with the Turbocharger Recirculation Valve, including rubber splits.
• Updating the valve with the latest part.
• Checking for TSB (Technical Service Bulletins) related to the issue.

Final Fix:
The final fix involved:

• Identifying a torn diaphragm in the boost pressure regulation valve.
• Replacing the valve.
• Clearing the codes.
• Testing the vehicle, and all is good now.

The P1602 code related to the power supply was also mentioned, but it was suggested to fix it first to ensure proper voltage supply to PCM-controlled circuits.

The issue was successfully resolved by replacing the boost pressure regulation valve.

Case #3: Chevrolet

Vehicle Information:

• Make: 2004 Chevrolet
• Model: Silverado 2500 HD
• Engine: 6.6L

Issue + Repair History:
The truck had the following issues:

• Code P0045 (T/C solenoid circuit fault).
• Code P0299 (T/C underboost) also appeared after driving for a while.
• The truck experienced a lack of power at times.

Other OBD2 Codes + Test Results:

• P0045: T/C solenoid circuit fault
• P0299: T/C underboost

What People Suggest to Fix Issue:
Community suggestions included:

• Checking the wiring harness around the driver’s side for chafing that could cause the P0045 code.
• Repairing the lower DTC (P0045) first and then rechecking the P0299.
• Replacing the fuel filter, as restricted filters can cause various issues, including low power and altered shift points.
• Taking the truck for a hard test drive with several wide-open throttle runs to potentially clear the P0299 code.

Final Fix:
The final resolution involved:

• Advising the customer to drive the truck more aggressively to get the turbo to work.
• This approach seemed to keep the MIL (Check Engine Light) off.
• It was also discovered that the truck was still under warranty, so any further problems would be addressed by the dealer.

The specific cause of the issues was not mentioned, but the recommendation was to address the lower DTC (P0045) first and observe the truck’s performance.

Case #4: Porsche

Vehicle Information:

• Make: 2009 Porsche
• Model: Cayenne Turbo S
• Engine: 4.8L

Issue + Repair History:
The vehicle had the following issues:

• Initially had 4 codes, with P1248 being cleared, but P1248 kept coming back.
• Boost gauge on the dash didn’t move or show any pressure.
• Set code P0299 (Turbocharger under boost) after test driving.

Other OBD2 Codes + Test Results:

• P1248: Initially present but cleared.
• P0299: Turbocharger under boost (appeared after test drive).

What People Suggest to Fix Issue:
Community suggestions included:

• Starting with a smoke test on the induction system to check for leaks in the charge line.
• Checking the pressure sensors to ensure they are reading correctly.
• Investigating vacuum lines for damage.
• Inspecting for leaks in the intake system or a cracked intercooler.
• Recommending the use of a Drive Pro scanner or a Porsche PWIS tester for diagnostics on the Porsche Cayenne.
• Considering vacuum leaks as a potential cause of the issue.
• Performing a smoke test for underboost diagnosis.

Final Fix:
The final resolution involved:

• Performing a smoke test on the induction system.
• Identifying a seized turbo, specifically on the right side.
• Recommending the replacement of both turbos, along with oil feed lines and hardware.
• Waiting for customer approval for the recommended repairs.

The issue was attributed to a seized turbo, and the recommendation was to replace both turbos to address the problem.

Case #5: Volkswagen

Vehicle Information:

• Make: 2006 Volkswagen
• Model: Jetta 2.0T
• Engine: 2.0L

Issue + Repair History:
The vehicle had the following issues:

• Code P0299 (Turbo underboost) cleared 2 weeks ago but returned.
• Code P2293 (Fuel pressure regulator) also appeared this time.
• The engine was running and operating normally.
• The customer mentioned that the issue occurred on the freeway at high speeds.

Other OBD2 Codes + Test Results:

• P0299: Turbo underboost
• P2293: Fuel pressure regulator

What People Suggest to Fix Issue:
Community suggestions included:

• Investigating the turbo recirculating valve (N249) and checking for a broken diaphragm.
• Checking for worn cam lobes on the intake camshaft, which could affect the high-pressure fuel pump.
• Replacing the high-pressure fuel pump and cam follower if wear is found.
• Replacing the N249 valve with the redesigned part (part# 06H 145 710 D).
• Checking for turbo pipe leaks, wastegate operation, and vacuum pipe integrity.

Final Fix:
The final resolution involved:

• Identifying a broken diaphragm in the turbo recirculating valve (N249).
• Replacing the N249 valve with the redesigned part (part# 06H 145 710 D).
• Checking for a worn cam lobe on the intake camshaft, which could affect the high-pressure fuel pump.
• Recommending further inspection and potential replacement of the high-pressure fuel pump and cam follower if wear is found.
• Ensuring the fuel pressure is within the normal range.
• Considering other factors such as electrical fuel pump in the fuel tank, fuel pump control module, and turbo pipe leaks.

The issue was addressed by replacing the N249 valve, and further inspection and potential repairs were recommended for the fuel pressure regulator and high-pressure fuel pump if necessary.

Advice	Diagnostic Step Description
Check for turbo recirculating valve (N249)	Inspect the N249 valve for a broken diaphragm.
Investigate intake camshaft wear	Examine the intake camshaft for worn lobes affecting the high-pressure fuel pump.
Replace high-pressure fuel pump and cam follower	If wear is found on the cam lobe, consider replacing the high-pressure fuel pump and cam follower.
Verify fuel pressure	Ensure that the fuel pressure is within the normal range.
Check for turbo pipe leaks	Inspect turbo pipes for splits or leaks.

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