I have a 87 Max where I am trying to test the 3 wire O2 sensor circuit before I replace the sensor. The car has 60K miles and has poor fuel mileage. The cyl head temp sensor connection was repaired and the ECM flashes 44 code that it is operating correctly in mode 3. But, the ECM does not flash the proper code that the O2 circuit is operating correctly in operating mode 1, so there is a problem here. One of the tests the manual says to check for is ground back through the harness with the O2 connector disconnected. But if you check the circuit diagram the harness returns this lead back to pin 152 on the ECM computer , not to ground. I measured open circuit on this lead. I understand the case of the O2 sensor is grounded, but this is on the sensor side. Should this harness lead be to ground or to the computer?
- posted
15 years ago