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

Check fuses for power to ECU.
Spin them in their holders or test each one with a test lamp on BOTH sides to ground.

ECU fuse is the OVP fuse i thought. I opened the fuse box and none are labeled ECU or anything close to that. All fuses look good in the under hood fuse box. Any other suggestions please?

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1972 450SL
1982 300D Turbo

Looks good means nothing on Benz fuses..you want to test each side w/test light.

I will see if I can bring up schematic..........

I just tested all the fuses yet again with a test light. probed both ends with test lamp. They are all ok. In any case none of them are labeled for ECU or anything close to engine management. I thought it was the OVP that powered the CIS. Also please note that i tested the connector to the CIS for ground and power and it was good, power is getting to the ECU (CIS).

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1972 450SL
1982 300D Turbo

Fuse 7 OK ????

Looking at another angle... Are you running NORMAL water temp? I have had a few American cars not go into closed loop because of a faulty engine coolant thermostat. They were running too cool.

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.

Running at normal operating temp (>80C)

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1972 450SL
1982 300D Turbo

I don't even get current through the EHA with KOEO (spec is 20mA). Same no current with engine running. My first thoughts were a burnt out EHA but it ohms out to 20ohms. I also get no signal (V, freq or duty cycle) off of pin 3 of the diagnostic round connector.

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1972 450SL
1982 300D Turbo

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