DTC 56 - Injection Pump Calibration Resistor Error: Notes

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1994 GMC Yukon, 1994 GMC Suburban, 1994 GMC Pickup, 1994 GMC Cab & Chassis, and 1994 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.

The PCM uses a calibrated resistor mounted internally in the injection pump to determine fuel rates. The resistor value is stored in the PCM memory. If the PCM memory has been disturbed or the PCM has been replaced, the PCM will relearn the resistor value on the next ignition cycle.

DTC 56 will set when PCM has lost it's memory and is unable to read a resistor value on the next ignition cycle. Possible poor performance problem. PCM will default to the MIL will light and, a current and history DTC 56 will set. PCM will default to the lowest fuel table.

NOTE: Test numbers refer to numbers on diagnostic chart.

This step determines if DTC 56 is the result of a hard failure.