DTC 18

DTC 18 Pump Cam Reference Pulse Error:

Pump Cam Reference Pulse Error:

CIRCUIT DESCRIPTION
The optical sensor also provides a pump cam signal to the Powertrain Control Module (PCM) by counting pulses on the sensor disk located in the injection pump. The pump cam reference signal is one of the most important inputs used by the PCM for timing and start of injection.

DIAGNOSTIC TROUBLE CODE (DTC) 18 WILL SET WHEN
8 cam reference pulses missed for every crankshaft position pulse.

ACTION TAKEN (PCM will default to)
Backup fuel.

DTC 18 WILL CLEAR WHEN
The fault condition(s) no longer exist, and the ignition switch is cycled "OFF then "ON."

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step determines if it is the result of a hard failure or intermittent.
2. This step checks 5 volt reference circuits.
3. This step checks ground circuit.
4. This step checks to see if the sensor is sending a signal to the PCM and to check CKT 982 for an open.

DIAGNOSTIC AIDS
When the PCM is in backup fuel, rough idle and poor performance problems will exist. If DTC 17 is stored, there is a possible problem with CKTs 474 or 987.

^ To further aid in diagnosing "intermittents", vehicle should be test driven with coolant temps above 85°C (185°F).