DTC 17

DTC 17 - Spark Reference Circuit:

Ignition Control Module Wiring Circuit:

Circuit Description:

The spark reference signal (CKT 647) is used by the PCM to improve ignition timing accuracy during crank and at engine speeds of up to 1200 RPM. The spark reference circuit allows the use of ignition control mode below 400 RPM, eliminating the need to utilize module mode during startup, and also allows the PCM to calculate true crankshaft position in 1/6 the time that use of the fuel control reference signal would permit.

During normal operation, the PCM uses the spark reference signal to control ignition timing until the engine speed exceeds 1200 RPM, at which time the fuel control reference signal (CKT 430) is used. When conditions for setting DTC 17 exist, the fuel reference signal is used by the PCM to control ignition timing advance. This condition will cause module mode to be used for ignition timing advance below 400 RPM and IC ignition timing to be degraded below 1200 RPM. DTC 17 will be set if:

^ The engine is running.
^ The PCM detects 150 fuel control reference pulses (50 crank revolutions), and no spark reference pulses.
^ Engine RPM is below 1200.

DTC 17 does not illuminate the MIL (Service Engine Soon).

Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.
1. Verifies that CKT 647 is not shorted to ground or open in the ignition jumper harness.
2. If a window on the harmonic balancer is interfacing with the 18x Hall-effect switch, the ignition control module will ground the spark reference signal. Starter may have to be bumped several times to obtain a voltage reading.
3. Voltage reading should be lower than that obtained with engine not running indicating a pulsed reference signal.

Diagnostic Aids:

An intermittent may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation.

Check for:
^ Backed out connector terminals or broken down insulation in CKT 647.
^ If connections and harness check OK, try monitoring voltage on CKT 647 with DVM while moving the related wiring harness and connectors with the engine idling. This may help to isolate the location of the malfunction.