I have a 1996 F150 4x4 with the 300. Getting three codes in this order: 411, 401, 420. Need ideas on what exactly to check, how to check it, etc. I'm tired of the check engine light coming on. Any help would be great!

 

A 1996 F150 should display Pxxxx OBD-II codes. Are we to assume those codes are P0411, P0401 and P0420?

 

Yea it's just how they are displayed on my scanners.

 

IIRC the common issue for a p0420 code is usually a failing cat causing the rear 02 to not function properly


For the p0401 and 411 I'd look for vacuum leaks.

 

PO401 is a CM only code:

Diagnostic Trouble Code (DTC) P0401 indicates that Continuous Memory Self-Test has detected insufficient EGR flow.

Possible causes:

-- EGR valve stuck closed or iced.

-- EGR valve diaphragm leaks.

-- EGR valve or flow path restricted.

-- EGR vacuum hose off, plugged or leaks.

-- VPWR circuit open to EGR Vacuum Regulator (EGR V.R.) solenoid.

-- EVR circuit to PCM open.

-- EVR circuit to PCM shorted to PWR.

-- Differential Pressure Feedback EGR (D.P.F. EGR) sensor pressure hoses both off.

-- D.P.F. EGR sensor pressure hoses reversed.

-- D.P.F. EGR sensor VREF circuit open.

-- Downstream pressure hose off.

-- Downstream pressure hose plugged.

-- Damaged orifice tube assembly.

-- Damaged EGR V.R. solenoid.

-- Damaged D.P.F. EGR sensor.

-- Damaged PCM.


P0411 can be displayed in the KOEO, CM or KOER tests. When was it displayed? The definition is defined as:

DTC P0411 indicates that Secondary Air is not being diverted when requested.

Possible causes:

-- Vacuum hoses damaged.

-- AIRB/AIRD valve inoperative.

-- Air Pump inoperative.

-- AIRB/AIRD solenoids damaged.

l Visually inspect vacuum lines for disconnects in the AIR system.

l Visually inspect for proper vacuum line routing. Refer to VECI decal.

l Visually inspect Air Pump for broken or loose Air Pump Belt.


Code P0420 is a CM only code:

Diagnostic Trouble Codes (DTC) P0420 and P0421 indicate that bank 1 catalyst system efficiency is below the acceptable threshold.

Possible causes:

-- Use of leaded fuel.

-- Oil contamination.

-- Cylinder misfiring.

-- Damaged HO2S.

-- Damaged ECT sensor.

-- Downstream HO2S wires improperly connected.

-- Fuel pressure too high.

-- Damaged exhaust system pipe.

-- Damaged exhaust manifold.

-- Damaged muffler/tail-pipe assembly.

-- Damaged catalytic converter.