Here is a tutorial to fix Ford Focus Mechanical CEL Heater,the problem will cause the check engine light on.

 

What You Need?

Strong drill
1/2″ drill bit
Vise (preferably)
Crescent wrench
Anti-seize copper sealant
Jack and jack stands

 

Procedures:
1) First off, you need to check how many o2 sensors you have.

2) If you have THREE like in the picture, you will need to buy TWO packages of these:

There should be two anti-foulers in each package. Get these exact ones. You can find them at Pep Boys, Kragen and most auto parts stores. If you only have TWO o2 sensors in your exhaust manifold, then you will only need one package.

3) Now, you’ll need a 1/2″ drill bit, a vise and a fairly strong drill. Make sure your drill bit is sharp. You will need to drill a 1/2″ hole using the drill bit through the anti-fouler, essentially opening up the hole that already present. For people that have THREE o2 sensors on their header, you will need to drill two of these anti-foulers. YOU NEED TO DRILL ALL THE WAY THROUGH THE ANTI-FOULER, OTHERWISE THE o2 SENSOR WILL NOT SCREW ONTO IT.

 

4) Ok, so now you will want to disconnect and unscrew the #2 and #3 o2 sensors from the car. For those that only have two o2 sensors, you only need to disconnect the last sensor. You’ll need to jack up your car to access the #3 o2 sensor, so take car doing that. Put it under a jack stand or two.

5) Take one drilled anti-fouler and screw it on top of an un-drilled anti-fouler. Use some anti-seize on the threads. Now screw the #3 o2 sensor on top of the the drilled anti-fouler. Use some anti-seize on these threads as well, but don’t overdo it and slop it all over the sensor. Screw this double anti-fouler assembly into the header bung, using anti-seize on the threads again. (For those of you that just have two o2 sensors, do this step for the #2 sensor; you are done)

6) Now take the other anti-fouler you drilled and install that on the #2 o2 sensor, using anti-seize. Here’s how it should look:

And just for clarification, do NOT put any anti-foulers on your primary o2 sensor. That one monitors your engine and has nothing to do with emissions. LEAVE IT ALONE!!

7) Make sure everything is tightened down. Unplug the battery for 10 mins. Plug it back in, lower the car from the jacks and take it for a spin. Hopefully you have the same luck as me and your CEL should not come on again.