EGR Cooler Efficiency Below Threshold
2009-2013 Audi A3 2.0L TDI
Description
The EGR cooler is not reducing exhaust gas temperature sufficiently. This can indicate an internal leak or coolant passage blockage.
Symptoms
- Check Engine Light
- Elevated intake manifold temperature
- Increased NOx emissions
- Coolant level dropping slowly
- White smoke from exhaust (coolant)
- Sweet smell from exhaust
Common Causes
- EGR cooler internal leak
- EGR cooler coolant passage blocked
- EGR cooler fins clogged with soot
- Thermostat affecting coolant temperature
- Insufficient coolant flow through cooler
Diagnostic Steps
- Compare EGR cooler inlet and outlet temperatures
- Check coolant level and condition
- Pressure test EGR cooler
- Inspect exhaust for coolant contamination
- Monitor coolant consumption
Repair Notes
Replace EGR cooler if leaking or if efficiency cannot be restored. An internal leak can cause catastrophic engine damage from hydro-lock.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0011Intake Camshaft Position Timing Over-Advanced Bank 1
- P0012Intake Camshaft Position Timing Over-Retarded Bank 1
- P0013Exhaust Camshaft Position Actuator Circuit/Open Bank 1
- P0014Exhaust Camshaft Position Timing Over-Advanced Bank 1
- P0015Exhaust Camshaft Position Timing Over-Retarded Bank 1
P3871 on Other Vehicles
Common Questions
What does code P3871 mean on a 2009-2013 Audi A3?
P3871 stands for "EGR Cooler Efficiency Below Threshold". The EGR cooler is not reducing exhaust gas temperature sufficiently. This can indicate an internal leak or coolant passage blockage.
What are the symptoms of P3871 on a Audi A3?
Common symptoms of P3871 include: Check Engine Light, Elevated intake manifold temperature, Increased NOx emissions, Coolant level dropping slowly, White smoke from exhaust (coolant), Sweet smell from exhaust.
What causes P3871 on a 2009-2013 Audi A3?
Common causes of P3871 include: EGR cooler internal leak, EGR cooler coolant passage blocked, EGR cooler fins clogged with soot, Thermostat affecting coolant temperature, Insufficient coolant flow through cooler.