Jim Grant's Tech Tips
'96 GMC Jimmy, Service Engine Soon
took my '96 GMC Jimmy to a local parts store to have them diagnose why
my service engine soon light is always on. Their tool came back with a
1406 diagnostic code. They told me I would need to take it to my dealer
for service. Can you tell me what diagnostic code 1406 really means? The
vehicle runs fine and gives no indication of any problems aside from the
- Dave B.
A '96 GMC Jimmy with
that code, I'm willing to bet coffee, that there is some carbon causing
the EGR valve to stick open just a bit. There is a sensor on the EGR valve
that reports the position of the valve to the computer. More often than
not carbon deposits will cause the EGR valve to not close completely.
The computer knows this because the voltage signal from the sensor on
the EGR valve is not what it remembered it to be. As far as the computer
is concerned if it isn't where it's suppose to be then there is a problem
and the check engine light turns on. The fix is often just a cleaning.
I would also suggest installing an aftermarket EGR gasket that has a screen
to trap the carbon that causes this problem.