Exhaust Pressure Control Valve High
Table of contents
- Possible Causes
- How To Fix
- Tech Notes
- Cost To Diagnose
- When is the code detected
- Possible Symptoms
- Description
P0478 AUDI Possible Causes
- Faulty Exhaust Back Pressure Valve
- Exhaust Back Pressure Valve harness is open or shorted
- Exhaust Back Pressure Valve circuit poor electrical connection
How do I fix code P0478 AUDI?
Check the “Possible Causes” listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector’s pins.
Tech Notes
- Check the Exhaust Back Pressure Valve (EBPV) butterfly valve is opening and closing freely and not sticking. If it seems to move freely you can then check the connector and circuit for the EBPV solenoid.
Cost of diagnosing the P0478 AUDI code
The cost of diagnosing the P0478 AUDI code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle’s make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
When is the code detected
Problems with either the Exhaust Back Pressure (EBP) Device or the tube between the exhaust manifold and the EBP sensor can be detected during the exhaust back pressure step test, in which the Engine Control Module (ECM) commands and then measures a specific preprogrammed pressure and then measures time for pressure decay during the engine running test.
If the ECM detects an Exhaust Back Pressure (EBP), Engine Oil Temperature (EOT) or Intake Air Temperature (IAT) sensor fault it will disable the exhaust back pressure regulator.
Possible Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
P0478 AUDI Description
Exhaust Back Pressure Regulator – Is a variable position valve that controls exhaust back pressure during cold ambient temperatures to increase cab heat and decrease the amount of time needed to defrost the windshield. The Engine Control Module (ECM) uses the measured exhaust back pressure, (ambient) intake air temperature, engine oil temperature and engine load to determine the desired exhaust back pressure. Valve position is controlled by switching the output signal circuit to 12 volts inside the ECM. On/off time is modulated from 0 to 99 % dependent upon the exhaust back pressure desired.
Upon each initial engine start-up, the ECM exercises the exhaust back pressure valve by commanding it to cycle on and off once. If upon start-up the temperature of intake air sensed by the Intake Air Temperature (IAT) sensor is < 37°F (5°C) and the oil temperature sensed by the Engine Oil Temperature (EOT) sensor is between 32°-140°F (0-60°C) it will continue to keep the back pressure valve partially closed. As the oil temperature rises during engine operation, the ECM will control the valve in response to the rising oil temperature.
