Code 41 - Fuel Always Lean
After starting engine, allow at least 2 minutes of idling before testing. Disconnect "Functional Test" trigger wire. Do not block throttle open as Idle Tracking Switch will be activated and invalidate test results.
- Disconnect MCU connector and oxygen sensor. Turn all accessories off. Measure resistance between ground and MCU connector pins 3 and 23. If resistance is less than 1000 ohms in either case, repair short. If resistance is greater than 1000 ohms, go to next step.
- Check continuity between MCU connector pin 3 and oxygen sensor connector (harness side). If resistance is greater than 5 ohms, repair wire. If less than 5 ohms, go to next step.
- Reconnect MCU and oxygen sensor. Disconnect harness from Fuel Control Solenoid (FCS). Check resistance of FCS coil. Resistance should be between 28-66 ohms. If resistance is within range, proceed to next step. If resistance is not within range, replace FCS.
- Reconnect FCS and connect voltmeter to back of solenoid harness connector. Start engine and maintain a speed of 2500 RPM. Observe voltmeter after 55 seconds. If voltage is less than 10 volts, proceed to next step. If voltage is greater than 10 volts, replace MCU.
- Disconnect thermactor air supply hose from the air pump, and plug hose. Raise engine speed to 2500 RPM and hold choke 3/4 closed to force the system rich. With voltmeter still connected to FCS, observe voltage after 55 seconds. If voltage is less than 10 volts, proceed to next step. If voltage is more than 10 volts, check for lean carburetor, and thermactor air.
- Turn engine off. Disconnect oxygen sensor connector and check resistance between harness side of connector and ground. If resistance is less than 1000 ohms, replace MCU module. If greater than 1000 ohms, go to next step.
- With oxygen sensor disconnected, start engine. With engine idling, connect a jumper wire to harness side of oxygen sensor connector. Be sure this connection cannot contact ground. Connect the other end of jumper to battery positive terminal, then raise engine speed to 2500-2800 RPM. Measure voltage at FCS after 55 seconds. If voltage is less than 10 volts, replace MCU. If voltage is more than 10 volts, replace oxygen sensor.