P0135 Cooling fan runs all the time

Fix codeP0135 Cooling fan runs all the time

If you own a Ford Escort or Mercury tracer and encounter a situation where the radiator fans run all the time, or you have a check engine light and trouble code P0135, you may have a shorted oxygen sensor. The official definition of a P0135 is Oxygen Sensor Heater Circuit Malfunction (Bank 1 Sensor 1). That’s the sensor before the catalytic converter. Oxygen sensors have a heating element in them to speed up their ability to sense oxygen in the exhaust stream. However, if that heater shorts out, it draws more current and that can melt the electrical connector, causing another short that powers the cooling fans non-stop. Find the white electrical connector located near the PCM and check for indications of overheated plastic. If the connector is distorted in any way, repair the damage with a new pigtail connector (from Ford) and replace the shorted oxygen sensor and the problem should disappear.

© 2012 Rick Muscoplat