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Code 41 - Fuel Always Lean

Run engine at 2000 RPM for 1 minute, then retest to ensure code still appears. If code still appears, disconnect jumper wire from Self-Test connector and proceed.

CAUTION: To prevent damage to the oxygen sensor, never connect ohmmeter to the sensor. Use DVOM with more than 10 megohms input impedance.
  1. Turn ignition off. Disconnect oxygen sensor, then connect a jumper wire from oxygen sensor to vehicle harness. Connect DVOM between engine block and jumper wire. Start engine and run at 2000 2300 RPM while applying 9-18 in. Hg to vacuum switch assembly. Wait 2 minutes, then check voltmeter. If voltage remains below 0.5 volts, go to next step. If voltage remains above 0.5 volts, go to step 4). If voltage alternates above and below 0.5 volts, go to step 13).
  2. Reconnect oxygen sensor to vehicle harness, then disconnect Thermactor air hose at pump. Disconnect MCU connector and connect DVOM between MCU connector pin 3 and engine ground. Place carburetor on high idle cam, then depress CVR rod on top of carburetor to force system rich. If voltage is less than 0.5 volts, go to next step. If greater than 0.5 volts, proceed to step 5).
  3. Turn ignition off. Disconnect oxygen sensor from vehicle harness (with MCU still disconnected). Connect ohmmeter between MCU connector pin 14 and ground. If resistance is 5 ohms or less, proceed with test. If resistance is more than 5 ohms, repair circuit.
  4. With ignition off, disconnect MCU harness connector and oxygen sensor. Connect ohmmeter to oxygen sensor connector (vehicle harness side) and MCU connector pin 3. If resistance is less than 5 ohms, proceed with test. If greater than 5 ohms, repair circuit. Check for a grounded oxygen sensor circuit by connecting an ohmmeter from MCU connector pin 3 to ground. If resistance is less than 1000 ohms, repair circuit. If resistance is 1000 ohms or more, replace oxygen sensor.
  5. Reconnect all wiring, then start engine and run on low step of fast idle cam. Disconnect harness from feedback motor (FBCA) on carburetor. Let engine run 2 minutes, then apply at least 15 in. Hg vacuum to zone switch assembly. Connect a known good feedback motor (with shaft fully depressed) to vehicle harness. While observing motor shaft, disconnect PCV hose from carburetor. If shaft does not extend, go to next step. If shaft extends within 10-15 seconds, reconnect PCV and Thermactor hoses and go to step 9).
  6. Turn ignition off. Disconnect MCU harness connector and feedback motor connector. Use an ohmmeter to check continuity of circuits from feedback connector to MCU connector. If resistance is more than 5 ohms in any circuit, repair circuit. If less than 5 ohms in all circuits, go to next step.
  7. Connect 1 ohmmeter lead to FBCA terminal 687 (terminal that connects to Gry/Yel wire of harness) and other ohmmeter lead to each of 4 outside FBCA terminals in turn. Measure resistance of each FBCA winding. If all resistances are 50-175 ohms at room temperature or above, proceed with test. If any winding is more or less than 50 175 ohms, replace FBCA motor.
  8. Connect 1 ohmmeter lead to engine ground. Check all circuits in feedback harness connector (except Gry/Yel) for continuity with ground. If resistance is more than 1000 ohms in all circuits, go to next step. If not, repair circuit.
  9. With ignition off, connect ohmmeter lead to feedback motor case (FBCA) and other lead to terminal 687 of motor. If resistance is less than 190,000 ohms, replace motor. If greater than 190,000 ohms, go to next step.
  10. Remove feedback motor from carburetor. Check for sticking shaft or dirt. Connect harness to motor and turn ignition on. Shaft should extend, then retract when ignition is turned off. If motion is uneven or shaft rotates, replace motor. Reinstall motor in carburetor.
  11. Turn ignition off and disconnect vehicle harness from TAD solenoid. Connect an ohmmeter across TAD solenoid leads. If resistance is 50-100 ohms, go to next step. If not, replace TAD solenoid.
  12. Disconnect MCU connector and TAD connector. Measure resistance between ground and pin 10 in MCU connector. If less than 1000 ohms, repair circuit. If more than 1000 ohms, reconnect MCU and go to next step.
  13. Check connections and operation of TAD solenoid and valve. If wiring and hoses are properly connected, check for carburetor leaks, hose routing errors, and operation of bowl vent solenoid.
Fig 1: Fuel Always Lean Test Connections
G206
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