Code 48, EGR Flow Test Failure

Code will set if current Codes 13, 17, 42, 43, 44 and 45 are not set, history or current Codes 14, 15, 21, 22, 24, 31, 32, 34 and 75 are not set, vehicle has been in closed loop for at least 9.2 minutes, coolant temperature is 80-110°C, MAP is 50-80 kPa, engine speed 1250-1850 RPM, vehicle speed is at least 35 MPH, rear short term fuel trim is less than 135 counts, EGR commanded to maximum, system voltage at least 11 volts and all conditions have been present for at least 5 seconds.

1. Ensures EGR is allowing exhaust flow and PCM is capable of controlling EGR valve.
2. Ensures EGR valve control circuit is not shorted to ground.
3. Ensures EGR valve control circuit or ignition filter circuit is not open and PCM is not at fault.

Fig 1: Code 48 Schematic (4.0L) EGR Flow Test Failure

Fig 2: Code 48 Diagnostic Flow Chart (4.0L) EGR Flow Test Failure