Test 5 EGO Always Lean (Code 41)

Fig.8 - MCU System Wiring Circuit:

CAUTION: To avoid damage to sensor, never connect an ohmmeter to sensor. Use a voltmeter with an input impedance of 10 megohms or greater.


1. Start engine and accelerate to 2000 rpm for 60 seconds, then retest to make sure that condition still exists before proceeding.

2. Disconnect jumper wire from Self-Test Trigger input circuits 201 and 60, Fig. 8.

3. With ignition key off, disconnect EGO sensor at harness, then connect a jumper wire between vehicle harness connector and EGO sensor connector.

4. Connect a voltmeter between engine block ground and metal clip of jumper wire. Make sure that there is a good connection between the two connectors.

5. With engine on and at 2000-2300 rpm, apply 9-18 inches Hg vacuum to zone vacuum switch assembly. Wait 120 seconds then observe voltmeter. If voltage is steady then alternates above and below .50 volts, proceed to step 3 under Test 9, Thermactor Air Diverter Solenoid (TAD). If voltage remained under .50 volts, proceed to the next step. If voltage remained above .50 volt, proceed to step 12.

6. Reconnect EGO sensor to vehicle harness, then disconnect Thermactor air hose at air pump.

7. Disconnect vehicle harness connector from MCU, then connect a voltmeter between engine block ground and circuit 94 of the harness connector, Fig. 8.

8. Place carburetor on high idle cam, then create a system rich condition by depressing the CVR rod and observe voltmeter.

9. If voltmeter indicates .50 volts or more, proceed to Test 6-Feedback Carburetor Actuator. If voltage is less than .50 volts, proceed to next step.

10. With ignition key off, disconnect vehicle harness from EGO sensor (MCU disconnected from harness), then connect a DVOM between engine block ground and circuit 94 of vehicle harness, Fig. 8.


NOTE: Do not touch metal portion of leads with hands while taking measurement.


11. If resistance is 1 megohm or shows an open circuit, replace EGO sensor. If resistance is greater than one megohm or less than 190,000 ohms, repair circuit 94 and retest.

12. With ignition key off, disconnect vehicle harness from EGO sensor and MCU, then connect an ohmmeter across circuit 94 of vehicle harness, Fig. 8. If resistance is less than 10 ohms, replace MCU. If resistance is 10 ohms or more, service circuit 94.