Audi S8 5.2L V10 Engine Power Loss and Exhaust Issues: A Diagnostic Approach

Experiencing a sudden loss of power in your Audi S8 5.2l V10 can be concerning, especially when accompanied by unusual exhaust behavior. This article delves into a real-world scenario where an Audi S8 owner faced these exact problems, providing a breakdown of the diagnostic process and potential areas of concern. If you are troubleshooting similar symptoms in your Audi S8 5.2L V10, understanding these diagnostic steps and fault codes can be invaluable.

Understanding the Symptoms: Power Loss and Uneven Exhaust

The owner of a 2007 Audi S8 reported a significant decrease in engine power. Alongside this, they noticed that exhaust gases were predominantly exiting from the left side (driver’s side in a LHD vehicle), with minimal output from the right side. This uneven exhaust flow is a critical symptom, suggesting a potential imbalance in engine operation between cylinder banks of the 5.2L V10 engine. The initial steps taken by the owner included replacing the ECM relay, fuel pump relay, and spark plugs, indicating a proactive approach to address common culprits. However, these actions did not resolve the issue, necessitating further diagnosis.

Diagnostic Trouble Codes (DTCs) Analysis: Unveiling the Faults

To gain deeper insights, a Ross-Tech VCDS scan was performed, revealing a comprehensive list of Diagnostic Trouble Codes (DTCs) across various modules. While numerous modules reported malfunctions, the engine modules (01-Engine and 11-Engine II) contained the most pertinent fault codes directly related to the performance issues. Let’s analyze the key DTCs from the engine modules:

Engine Control Module (ECM) Faults: Address 01 & 11

The scan revealed multiple faults, with some recurring in both engine modules, suggesting widespread electrical or sensor-related problems. Here’s a breakdown of the critical engine-related DTCs:

• 000802 – Engine Speed Sensor (G28) P0322 – No Signal: This fault indicates a failure or lack of signal from the Engine Speed Sensor (G28). This sensor is crucial for determining engine RPM and crankshaft position, essential for ignition and fuel injection timing. A missing signal can lead to severe performance issues and even prevent the engine from starting.
• 001112 – Evap System Purge Control Valve (N80) P0458 – Short to Ground: This points to an electrical short in the Evaporative Emission (EVAP) System Purge Control Valve (N80). While EVAP system issues primarily relate to emissions, a short circuit can indicate broader electrical problems within the engine management system.
• 005173 – Secondary Air Pump Relay (J299) P1435 – Short to Ground: Similar to the EVAP valve, this fault suggests a short circuit in the Secondary Air Pump Relay (J299). The secondary air pump aids in cold starts by reducing emissions. Again, the “short to ground” is a recurring theme, hinting at potential wiring harness or grounding issues.
• 005634 – Power Supply Terminal 30 P1602 – Voltage too Low: This is a significant fault, indicating low voltage at Terminal 30, which is a main power supply terminal. Low voltage can cause a multitude of issues with electronic components and sensors throughout the vehicle, including the engine control system.
• 005715 – Please check DTC Memory of ABS Controller P1653: This fault is a general request to check the ABS controller’s DTC memory and often appears when there are broader communication or power supply issues affecting multiple modules.
• 012312 – Valve for Exhaust Flap 1 (N321) P3018 – Short to Ground & 012322 – Valve for Exhaust Flap 2 (N322) P3022 – Short to Ground: These faults, related to the exhaust flap valves (N321 and N322), again indicate electrical short circuits. Exhaust flaps control backpressure and noise levels, and malfunctions can affect engine performance.
• 004199 – Intake Air Switch-Over Valve (N335) P1067 – Short to Ground: Another “short to ground” fault, this time for the Intake Air Switch-Over Valve (N335). This valve is part of the variable intake manifold system, optimizing airflow at different engine speeds. Malfunctions can impact engine breathing and performance.
• 005153 – Secondary Air Injection Solenoid Valve (N112) P1421 – Short to Ground: Continuing the pattern, this fault points to a short circuit in the Secondary Air Injection Solenoid Valve (N112), another component related to the secondary air injection system.
• 005494 – Right Engine Mount Solenoid Valve (N145) P1576 – Short to Ground & 005490 – Left Engine Mount Solenoid Valve (N144) P1572 – Short to Ground: Faults related to both left and right engine mount solenoid valves, both indicating “short to ground.” These valves control the active engine mounts, and while not directly related to engine performance in terms of power delivery, electrical faults here reinforce the pattern of widespread electrical issues.
• 006435 – Please Check DTC Memory of ECU Number 2 P1923: Similar to the ABS controller DTC check, this fault prompts checking the DTC memory of ECU Number 2 (Engine Control Unit II), again suggesting potential communication or system-wide issues.
• 008199 – Intake Manifold Flap; Bank 2 P2007 – Stuck Closed: This fault indicates a mechanical issue with the intake manifold flap on Bank 2 (typically the left bank in V engines). A stuck closed flap can restrict airflow to that cylinder bank, leading to reduced power and uneven exhaust flow, directly correlating with the reported symptoms.
• Oxygen (Lambda) Sensor Heating Circuit Faults (Multiple – B3 S1, B3 S2, B4 S1, B4 S2 – Short to Ground): Several oxygen sensor heating circuit faults, all indicating “short to ground,” further emphasize the electrical issues. Oxygen sensors are critical for fuel mixture control, and heater circuit faults can affect their accuracy and engine performance.

Communication and Voltage Issues Across Modules

Beyond the engine modules, numerous other modules reported “No Signal/Communication” or “Lower Limit Exceeded” faults, particularly related to voltage supply (Terminal 30) and communication bus issues (CAN Gateway, Roof Electronics, etc.). These widespread communication and voltage faults are crucial context. They strongly suggest a systemic electrical problem rather than isolated sensor failures. The “Voltage too Low” and “Short to Ground” errors across multiple systems point towards a potential issue with the vehicle’s power distribution, grounding, or battery/charging system.

Potential Causes and Diagnostic Path for the Audi S8 5.2L V10

Based on the symptoms and the extensive DTC list, particularly the recurring “Short to Ground,” “No Signal,” and “Voltage too Low” errors, several potential causes emerge:

1. Electrical System Faults: The prevalence of “Short to Ground” faults strongly indicates a wiring harness issue, a faulty ground connection, or potentially a problem within the ECU itself causing shorts. A thorough inspection of the engine wiring harness, ground points, and power supply circuits is essential.
2. Voltage Supply Issues: The “Voltage too Low” DTC and numerous communication faults suggest a potential problem with the battery, alternator, or voltage regulator. A voltage drop can cause various electronic components to malfunction and trigger a cascade of DTCs. Testing the battery’s health and the charging system’s output is crucial.
3. Intake Manifold Flap (Bank 2) Mechanical Failure: The “Intake Manifold Flap; Bank 2 Stuck Closed” DTC is highly relevant to the uneven exhaust symptom. A stuck flap on one bank would restrict airflow, leading to reduced combustion and exhaust output from that side. Physical inspection and testing of the intake manifold flaps are necessary.
4. Engine Speed Sensor (G28) Failure: The “Engine Speed Sensor No Signal” DTC is critical for engine operation. A faulty G28 sensor can directly cause power loss and running issues. Testing or replacing this sensor should be considered.

Next Steps for Diagnosis:

1. Detailed Electrical Inspection: Focus on checking wiring harnesses for damage, chafing, or corrosion, especially around areas where multiple “Short to Ground” faults are indicated. Verify ground connections are clean and secure.
2. Voltage and Charging System Test: Measure battery voltage at rest and during cranking. Test alternator output to ensure proper charging voltage.
3. Intake Manifold Flap Inspection: Access and visually inspect the intake manifold flaps, particularly on Bank 2, to check for binding or damage.
4. Engine Speed Sensor (G28) Test: Test the G28 sensor’s signal output using an oscilloscope or multimeter. Consider replacement if faulty.
5. Professional Diagnostic Assistance: Given the complexity and the number of fault codes, seeking professional diagnostic help from a qualified Audi technician is highly recommended. They possess specialized tools and expertise to pinpoint the root cause effectively.

Conclusion: Seeking Expert Audi Diagnosis

Diagnosing power loss and exhaust issues in an Audi S8 5.2L V10, especially with a multitude of DTCs, requires a systematic and thorough approach. While initial steps like replacing relays and spark plugs are common first actions, the extensive fault codes in this case point towards more complex underlying electrical and mechanical problems. The combination of “Short to Ground” faults, voltage issues, and intake manifold flap malfunction strongly suggests a need for expert Audi diagnosis to accurately pinpoint and resolve the root cause of the Audi S8 5.2L V10 engine problems.