Circuit Description
The linear EGR system consists of a linear EGR valve, the PCM, and its associated
wiring. The EGR valve solenoid is controlled directly by the PCM when certain conditions
have been met. The PCM contains a diode feedback circuit which dissipates energy when
the valve is cycled OFF. When the PCM grounds the valves, the diagnostic feedback
signal can determine if the valve had actually moved. DTC P0404 has been defined
to monitor the feedback signal. This diagnostic will determine if the position feedback
signal properly falls within the correct range under different valve operating conditions.
Conditions for Setting the DTC
| • | If the commanded position is greater than 80 percent, the actual
position must be within 26 counts, 10 percent (0.5 volts) of
commanded. |
| • | If the commanded position is less than 80 percent, the actual position
must be within 60 counts, 24 percent (1.1 volts) of commanded. |
| • | Two consecutive ignition cycles while the diagnostic runs with an active
fault |
DTC P0404 will set if either condition exists for greater than 10 seconds.
Important: The EGR position error is continuously checked
when the EGR is commanded ON.
Important: The EGR valve may operate at any engine coolant
temperature regardless of loop mode.
Important: When this DTC sets, some EGR functions will
be disabled for the duration of that ignition cycle. When repairs are complete, codes
must be cleared and the ignition keyed off for at least 10 seconds to allow
proper operation.
When either one of these tests have failed, a DTC will set and EGR will be disabled
for that ignition cycle. The malfunction history record will indicate which one of
these tests has failed to aid in diagnostics.
Diagnostic Aids
| • | Check for backed out or damaged terminals. |
| • | Check the tightness of the female terminal grip with a spare male terminal. |
| • | Check for B+ voltage at the E terminal on the EGR valve when the
ignition is ON. |
| • | Check the EGR 10-amp fuse in the UHJB before diagnosing this DTC. |
| • | Carbon build-up around the pintle valve may restrict pintle movement. |
| • | An open in the PCM diode feedback circuit will result in unstable valve
operation resulting in vehicle surge. |
| • | Due to moisture associated with the exhaust system, the EGR valve may
freeze and stick in extreme cold ambient conditions. |
