Problem: The vehicle was brought to the
shop because the MIL was on and the gas mileage was down. There
were no noticeable drivability issues.
Details: The technician pulled two DTCs:
P2196 (Lack of H02S-11 Switch, Sensor Indicates Rich) and P2198
(Lack of H02S-21 Switch, Sensor Indicates Rich). First he checked
the fuel pressure – it was at specifications. The fuel pressure
regulator was not leaking fuel into the vacuum line. The air
filter was new and the oil was not overfilled. With the scan tool
connected, he monitored the PIDs for the oxygen sensors. They
respond to vacuum leaks, but stayed around 900 millivolts.
Next, he connected an injector tester and performed a flow test.
He found several injectors that were flowing too much fuel.
Confirmed Repair: The technician replaced
the full set of injectors, cleared the codes and test drove the
vehicle. The oxygen sensor responded normally and the DTCs did
not return. Vehicle fixed!