Powertrain Controls - ECM/PCM

Diagnostic Trouble Code (DTC) 16:

Distributor Ignition System Circuit:

CIRCUIT DESCRIPTION
The distributor ignition system supplies two timing inputs to the Powertrain Control Module (PCM), a high resolution signal (180 pulses per one crankshaft revolution) and a low resolution signal (4 pulses per one crankshaft revolution). The PCM can determine if one of the timing inputs is not being received by comparing the two inputs. If the PCM detects the high resolution timing pulse without detecting the low resolution timing pulse, this Diagnostic Trouble Code (DTC) will set.

The reference signals toggle between 0 and 5 volts as the camshaft turns. Therefore, an open, a short to voltage, a short to ground, or a defective sensor inside the distributor can prevent the voltage from pulsing at the PCM.

DTC 16 WILL SET WHEN
The PCM detects 720 high resolution timing pulses before any low resolution pulses are detected.

ACTION TAKEN (PCM WILL DEFAULT TO)
DTC 16 will be stored in the PCM memory, but will not turn "ON" the Malfunction Indicator Lamp (MIL). Fuel pump and injector operation will be disabled.

DTC CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. If the engine starts at this point, DTC 16 is intermittent.
2. This test will determine if the PCM is sending out a signal to the distributor for processing. If this signal is not available or is shorted to ground or voltage, the distributor cannot ground it to produce reference pulses.
3. If a DTC 41 and/or 42 is also set with a DTC 16, and no external fault can be found, replace the PCM. If only DTC 16 is set and distributor connections are OK, replace the distributor.

DIAGNOSTIC AIDS
DTC 16 will set if the high and low resolution signal circuits are shorted to each other. Before replacing any components, make sure these circuits are not shorted together. If DTC 16 does not reset and the vehicle still does not start, refer to Diagnostic Charts/A Charts/Chart A-3. Related Tests, Information and Procedures

NOTE: When equipped with Opti-Spark distributor, if components must be replaced, check distributor vent system. Refer to Diagnostic Charts/C Charts/Chart C-4C. Chart C-4C Distributor Vent System Check

When an intermittent DTC 16 occurs, a misfire may be apparent. To locate an intermittent, use the Tech 1 scanner's Snapshot feature and try to duplicate the conditions under which the misfire is present. When reviewing the captured data, watch for any abnormal high and low resolution timing pulses. Refer to Diagnosis by Symptom/Cuts Out and Misses. Cuts Out/Misses