P2AA4
Cold Start EGR B Flow Excessive Detected
During cold start, the ECM detects that EGR channel B delivers more exhaust mass than commanded. Engine smoothness and warm-up calibration may be affected.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: hard
Symptoms
- Check engine light on
- Pinging or knocking under load
- Power loss and hesitation
- Possible rough idle
- Failed emissions inspection (NOx)
Common causes
Ordered by how often each turns out to be the cause.
- EGR valve stuck partially openCommon
- Actuator overshoots commanded positionPossible
Parts involved
- EGR Valve B
- EGR Cooler B
- EGR Diff Pressure Sensor
P2AA4 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.