Jim Grant's Tech Tips
'95 Ford Crown Vic, Engine Warning Light Always On
Ford Crown Vic runs fine but the engine warning light has been on since
last year. My code reader for the OBDII system indicates the code P0401,
which indicates a low EGR flow. The EGR valve, the relay and the coolant
sensor were replaced. I read at a car web site that the EGR sensor lines
are very narrow and require cleaning with a coat hanger and vacuum cleaner
to get out the carbon build up and was told that Ford has a lousy EGR
system. Do you have any ideas on the problem? I have a mechanical background
and understand auto electronics and repair, I just dont want to
keep replacing parts.
The computer code that youre referring to is most often the result
of a restricted passage in the EGR system. The Exhaust Gas Recirculation
(EGR) system feeds exhaust gases back to the engine. The original purpose
of this system was to reduce a rather nasty exhaust emission. Overtime
engineers found that with proper operation the EGR system would not only
reduce emissions, it would also reduce spark knock and improve fuel economy.
The computer in your vehicle has the ability to calculate the flow rate
of exhaust gases through the EGR system. If the flow rate drops, the computer
alerts the driver with the check engine warning light. I regret to inform
you that much of what you have replaced does not cause a low rate of flow
in the EGR system. The most common cause is restriction in the passages
for the system. The fix is likely a good cleaning of the plumbing for
the EGR system.