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Old 11-20-2002, 01:29 AM
dordal dordal is offline
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Join Date: Jul 2002
Posts: 30
W124 O2 Sensor Problem

Here is one for the smart minds: Computer tells me there is an O2 sensor problem. Two codes: 'Incorrect voltage from 02 sensor' and 'Heater amps too high/shorted'.

There is _no_ current to the O2 heater, and a continuity check finds an open circuit from pin 7 of the fuel pump relay, where the schematic says the O2 heater is connected. That would lead me to think there is a break in the wire, but that seems _very_ unlikely.

Meanwhile, the 02 sensor itself is reading only 0.1V, even after being heated up by exhaust. Normally I'd say its a bad sensor, but I just replaced it in April and it has less than 10K miles on it. Its an OEM sensor.

Any ideas? Is there a fuse on the heater wire that might have blown? I didn't see anything during 3+ hours of inspection.

The car is a 93 300E.
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