E046

TEST CONDITIONS
Always tested.

FAILURE CONDITIONS
Left bank fuel control block learn values differ from right bank fuel control block learn values by more than 15 counts.

ACTION TAKEN
1. ECM turns on "Engine Control System Fault" telltale;
2. ECM commands BCM to display "Service Now" message on Driver Information Center (DIC).

DESCRIPTION
The ECM controls right bank fueling based on the right side oxygen sensor and left bank fueling based on the left side oxygen sensor. Code EO46 sets when the left bank fueling differs (richer or leaner) than right bank fueling.

Likely causes of Code EO46 are
1. AIR management valves sending air to the left exhaust manifold.
2. Lean or faulty injectors on one side of the engine.
3. Cracked or fouled spark plugs.
4. Exhaust or intake manifold leak.

Notes on Fault Tree
1. Checking for the ECM's ability to control fuel delivery. If the engine has an excessive vacuum leak or is out of adjustment, the ECM may not be able to control fuel delivery. The fuel control system must be in control before diagnosing a Code EO46.
2. Checking for proper operation of the AIR management system. Code EO46 will set if AIR is being sent to the exhaust manifold. This will cause the left oxygen sensor to go lean and set a Code EO46.
3. Checking for proper operation of the AIR Divert Valve. The ECM should energize this valve sending air to the exhaust manifold.
4. Checking for proper operation of the AIR Switch Valve. The ECM should energize this valve sending air to the exhaust manifold.
5. Checking for proper ignition secondary operation. Fouled or cracked plugs may cause one bank to run richer or leaner than the other bank. Leaking or dirty injectors may also cause a fueling imbalance from bank to bank.
6. PFI chart A-4 will diagnose fuel system problems.
7. See "Notes on Intermittents" for diagnostic aids.

NOTE ON INTERMITTENTS
Select ECM data ED36 LINT and drive vehicle. If integrator value consistently rises from 128 to 150 or higher, check AIR switch valve for air being directed to exhaust manifold.

Check AIR management valve electrical connectors for corrosion or poor connection. Perform an injector balance test.