VCM-A Chart

Intake Manifold Tuning Valve Diagnosis:

CIRCUIT DESCRIPTION
The tuning valve is activated through a relay by the Vehicle Control Module-A (VCM-A) during periods of acceleration where engine RPM is over 3000 and throttle position is over 34%.

The tuning valve relay is powered by CKT 39 and turned "ON" and "OFF" when the VCM-A grounds CKT 1387. When the relay is activated, it applies voltage from CKT 39 to CKT 1015, thus opening the tuning valve.

CHART TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.
1. This step determines if the system is functioning at the present time.
2. By cycling the tuning valve "ON" and "OFF" will determine if the tuning valve relay is operating.
3. This will determine if the tuning valve relay has ignition voltage on ignition feed circuit.
4. This will determine if the tuning valve relay has ignition voltage on ignition feed circuit to splice.
5. This step will determine if the relay related wiring to valve or the tuning valve is at fault.
6. This step will determine if the VCM-A, tuning valve relay or related wiring is at fault.

DIAGNOSTIC AIDS
Throttle Position (TP) Sensor - An intermittent TP sensor output will cause the VCM-A to receive a false input.