Code 41:

• Code 41  - HEGO indication that the fuel system was lean for more than 15 seconds when the fuel system should have been in closed loop fuel control.
• Code 42  - HEGO indication that the fuel system was rich for more than 15 seconds when the fuel system should have been in closed loop fuel control.
• Code 43  - HEGO indicated that the fuel system was lean during WOT for more than 3 seconds.
• Code 65  - Closed loop not activated on HEGO switching.
• Code 85  - Excessive rich mixture condition corrected by adaptive fuel strategy.
• Code 86  - Excessive lean fuel mixture condition corrected by adaptive fuel strategy.

If an over-rich fuel condition is suspected or experienced, check ignition system. Burn off fuel deposits on HEGO by operating the vehicle at sustained high (legal) speeds followed by a few hard acceleration runs. This will allow the HEGO contamination to be burned off. Check the following areas:

Code 41:

• Intermittent HEGO signal (Signal or Ground circuit).
• If Code 65 also present, repair faulty HEGO circuit (Signal or Ground circuit).
• If Code 43 also present, service Code 43 first.
• Check VAF for leaks or sticking (caused by contamination or frost).
• Low fuel pressure at WOT, check fuel supply.
• Low fuel flow at WOT (pressure okay), check clogged injectors or low battery voltage.

Code 42:

• Intermittent HEGO signal (Signal or Ground circuit).
• Airflow meter indicating incorrect airflow, check for high voltage output due to sticking air vane ("flapper door").
• Excessive fuel flow, pressure regulator vacuum supply disconnected or blocked fuel return line.
• Excessive fuel flow, damaged or stuck open injector(s).

Codes 41 and 42:

• Intermittent HEGO signal (Signal or Ground circuit).
• Sticking air vane ("flapper door"), due to contamination.
• Contaminated HEGO sensor, lead or silicone fouled.

Code 43:

• Low fuel pressure at WOT, fuel pump or restricted supply.
• Low fuel flow at WOT, injectors plugged or low battery voltage (less than 11 volts).

Code 65:

• Check for faulty HEGO signal (Signal or Ground circuit).

Code 85:

• If Code 42 also displayed, service it first.
• Excessive fuel pressure, check regulator vacuum line and fuel supply line.
• Excessive fuel flow, check for damaged injector pintles or injector stuck open.

Code 86:

• If Code 41 also displayed, service it first.
• Low fuel pressure, low pressure pump or restricted fuel supply.
• Low fuel flow, clogged injectors or low battery voltage.