Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Check Eng light-99 Ford Ranger

99 Ford Ranger 4-cyl. Check engine light is on; pulled fault code: “catalyst efficiency below threshold, bank 1.” Cat converter is new as is rest of exhaust, o2 sensors are new, and its been recently tuned up. Any suggestions?

Is It PO420 Or Close To That ?
That’s One Of The Most Commonly Found Codes When Vehicles Trigger “Check Engine”.
Lots Of Things Can Be Culprits. It’s Not Necessarily The Converter.


Did You Turn Off The CEL ?
I’d Do That And See If/How Long It Takes To Set Again.

How Much Oil Does This Vehicle Consume (qts/miles) ?


There’s Quite A Bit Of Material In This Ford Technical Service Bulletin That Includes 1997-2001 F-150s.

Scroll down TSB 01-9-7, written for Ford technicians, and you’ll find Catalyst Efficiency Monitor - Information. It talks about PO420/PO430.


Agree with @CSA X 3.

@D-Man read pages 4 and 5

straight from the horse’s mouth

Do you have an aftermarket cat?

Oil consumption (excessive oil consumption can ruin a new cat)

How is your thermostat?
Taking forever to reach operating temperature?
Never reaches operating temperature?

A sluggish/stuck open thermostat could cause problems running/passing the cat monitor

I realize the exhaust is new, but make absolutely sure there are no leaks. That could help contribute to a false cat code

I also realize you say it’s been tuned up. Nevertheless, make absolutely sure there are no misfires of any kind. Remember, not all misfires are caused by bad plugs and wires. I’ve fixed my fair share of misfires which were caused by open circuit injectors or plugged injectors.

To be clear about what I said, misfires can ruin a new cat.

Thanks guys.