1989 260E Federal.
Car never goes into closed loop. No current through the EHA and O2 sensor does not oscillate. The O2 sensor was replaced and is good. O2 voltage moves up and down when I create a forced lean or rich condition. EHA shows 20ohms which is good. No duty cycle or frequency measured off of pin 3 of diag connector.
- I have a good OVP (fuses good too). Also checked with test lamp that the CIS is getting good power and ground.
- The check engine light comes on for 3 seconds as is normal during KOEO.
- I opened up the CIS case and nothing smells burnt, no cold solders and no obvious burnt components or traces.
- O2 signal is getting to the CIS computer but no closed loop (feedback) operation.
- With KOEO the O2 signal is 0V and it should be .4-.5V.

Please help.

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1972 450SL
1982 300D Turbo