Contour Enthusiasts Group Archives Forums General Troubleshooting Old Sensors gone and the light goes on

I have a 96 Contour 2.5 It keeps throwing a code P0156 which is the circuit for the downstream bank 2 sensor. I have replaced the sensor twice. All the other sensors have been replaced. Cleaned the upper intake and throttle body, not to mention the totally crudded egr valve passages, and checked the wiring going to the sensor. I cannot find anything wrong what so ever. You reset the computer and take off in it, the light will stay off till you turn it off and then restart it. After you restart it you go down the road a mile and it comes back on. When the light comes on the exhaust starts stinkin. So I know that if I drive it with the light on it will mess up my new oxygen sensors and tune-up from running rich. Im so fed up now I am debating on ramming it in the garage and leave it. Has anybody had this problem or could it just be the computer is bad and not throwing a code for it being bad. I have run out of ideas. Please can anybody help?

Blaze

Oxygen sensor codes don't necessarily mean that the oxygen sensor is bad.

The rear oxygen sensor monitors the cat. In this case, the pre cat in the exhaust manifold. If the rear oxygen sensor is switching nearly as rapidly as the front oxygen sensor, it is assumed that the cat is not working very well. I suspect that this may be your problem, so you need to investigate it a bit more.

�· Disconnected sensor
�· Pinched, shorted, corroded wiring or pins
�· Crossed sensor wires
�· Exhaust leaks
�· Contaminated or damaged sensor
�· Chafed/damaged wiring


Also where did you buy the sensor?

The reason I changed the sensors is because I gave it a tune-up. I figured it needed it and after looking at how black the plugs were it really needed it. The check engine light was on before I tuned it up. After it threw the code I then replaced the same oxygen sensor again and nothing changed. I am thinking there is a break in the wires somewhere. The ford dealer told me that it isnt a CAT code, it means that somewhere it is unplugged or the wiring is broke. Does anyone know where and if there is a big connector in the harness for this oxygen sensor. The service manual shows me the upstream one, but not the downstream one. It looks like it runs over the transmission, but I loose sight of it after it goes up the engine. Thanks

Blaze

Do an overlay to the pcm and the power supply for the heater. Get you a wiring diagram, use heat shrink with crimp connectors (don't solder), route your wiring carefully and use some conduit in the tight areas.


Want to know why you don't solder oxygen sensor wiring?

why?

An oxygen sensor measures the difference in concentration of oxygen in the exhaust stream and the surrounding air. It works with a minute quantity of air. Access to the exhaust stream is easy - stick a probe in it. Access to the surrounding air isn't so easy. When the sensor is new, the surface is clean. Drive it a few miles and a film starts to build up. after 10 or 20,000 miles, the outside has enough of a film that oxygen doesn't get to the sensor anymore. So the outside air is sensed by drawing air through the wires from the pcm. Remember all the connectors in the engine compartment have seals on them. And all the wiring is crimped. Air can pass through the crimps and in the small spaces around the wire strands. So the outside air is measured with air that comes from inside the pcm, drawn through the wires and pumped out by the oxygen sensor. The pumping action is accomplished by the heat of the sensor - air around it expands and draws air from the wiring... interesting, huh? If you solder the wires, the solder will fill the spaces that the air moves through and it will set a code for a lean condition...

Weird!!