Fixing check engine light codes 420 for Ford vehicles is sometimes a problematic issue. If you are not careful, most garages will automatically recommend replacement of the catalytic (cat) converter which is really expensive. Most Ford dealers usually cover it for 80,000 km but if your vehicle has too many miles, you are out of luck.
This is the meaning of this code:
420 is actually called P0420 which means Catalyst(catalytic converter) low efficiency bank 1
Here are some quick methods of diagnosing check engine light codes 420 for Ford vehicles:
1.) Make sure your vehicle has not been filled with leaded gas or worked on the engine using silicone. The catalytic converter of this engine easily deteriorates when exposed to leaded fuel and sealants such silicone when used internally such as intake manifold engine jobs.
2.) Scan the catalytic converter oxygen sensor located after the catalytic converter. Not to be confused with the exhaust manifold (upstream) oxygen sensor, this sensor is used purely to monitor the the catalytic converter efficiency whereas the engine performance is monitored by the upstream oxygen sensor. When reading the oxygen sensor voltage, the cat sensor usually fluctuates between 0.4v to 0.6v and has a lower range of fluctuation than the upstream oxygen sensor which is about 0.1v to 0.9v. Most mechanics will usually replace the cat if both upstream and cat oxygen sensors are switching at the same rate.
The check engine light codes 420 for Ford vehicles accompanied by misfiring at acceleration sometimes is caused by a bad air mass sensor which can be serviced by cleaning the mass sensor wire elements. When the 420 code is reset after servicing the mass sensor, this code should not come back if the mass sensor is OK. Otherwise, it confirms that the cat sensor has really failed. It is also a good idea to monitor the engine vacuum/egr flow and the engine fuel trim percentage readings using your generic scanner. If not done, both of these systems can damage your cat if not repaired before making any exhaust repairs.
Finally, if the engine has no performance problem and this check engine light codes 420 for Ford comes on, don’t rely too much in testing the cat back pressure because it does not take too much contaminants to make it fail. This is especially true if you have replaced the cat previously with an aftermarket catalytic converter. However, code P0420 accompanied by no engine performance usually means a defective cat.
Check engine light codes 420 for Ford vehicle Tips:
If your Ford vehicle has run out of warranty, always use OEM cat parts only, if using an aftermarket product, make sure the vendor will guaranty it in writing. Don’t even contemplate on using a used Cat because it is a waste of time.
If your cat has failed, then the oxygen sensor connected to it is not far behind. As a matter fact this is the best time to replace the sensor if it was not done before. If silicone sealant was used in the engine and the cat has failed, replaced both upstream and cat oxygen sensors.