Diagnostic Aids

An intermittent condition may be caused by poor or loose connection at ECM. This could cause a code to be falsely set.

Check all throttle body vacuum hoses and EGR valve. Check MAP sensor vacuum hose for leaks or restrictions. ECM will periodically turn off the EGR VSV when EGR is enabled in closed loop operation. Code 51 will set if corresponding manifold pressure change is less than a calibrated value, determining that a fault exists in the EGR system.

Fig 1: Code 51 Schematic Exhaust Gas Recirculation Circuit

Fig 2: Code 51 Flow Chart Exhaust Gas Recirculation Circuit