DTC 18, Pump Cam Reference Pulse Error: Notes
WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 1995 GMC Yukon, 1995 GMC Suburban, 1995 GMC Pickup, 1995 GMC Cab & Chassis, and 1995 GMC C3500 HD. However, it is still accessible from the selected car via links, so may be relevant.
Optical sensor also provides a pump cam signal to PCM by counting pulses on sensor disk located in injection pump. Pump cam reference signal is one of the most important inputs used by PCM for timing and start of injection. DTC 18 will set when 8 cam reference pulses are missed for every crankshaft position pulse. PCM will default to backup fuel.
NOTE:
Test numbers refer to numbers on diagnostic chart.
- This step determines if DTC 18 is result of a hard failure or an intermittent condition.
- This step checks 5-volt reference circuits.
- This step checks ground circuit.
- This step checks if sensor is sending a signal back to PCM and if an open is present in cam signal circuit.