VCM Controlled Generator Diagnosis. Chevrolet S10 Pickup

For 1990-2009 cars only

Makes 🢒 Chevrolet 🢒 1998 🢒 S10 Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 VCM Controlled Generator Diagnosis

Handling ESD Sensitive Parts Notice
Engine Controls Components
UBEC Power, Grounding, Generator, And MIL
OBD II Symbol Description Notice

Circuit Description

The VCM Controlled Generator Diagnostic is designed to diagnose the generator lamp terminal. The VCM provides a voltage signal to the generator L-terminal. The generator will charge the battery whenever it receives the VCM input. The generator voltage regulator will pull the terminal input low when the engine is not running or the generator is not working properly. Any interruption in the VCM input will cause the generator to stop charging.

Diagnostic Aids

The VCM communicates to the IP through the Class 2 serial data line. Check for any Class 2 DTCs that would indicate a loss of communication between the VCM and the IP.

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

Thoroughly check any circuitry that is suspected of causing the intermittent complaint for the following conditions:

•	Backed out terminals

•	Improper mating

•	Broken locks

•	Improperly formed or damaged terminals

•	Poor terminal to wire connections

•	Physical damage to the wiring harness

•

Corrosion

•	Moisture in the connector

Test Description

If the IP voltmeter does not read near the voltage reading displayed on the DMM at the generator output terminal, the IP gauge or related IP wiring could be the problem.

If the generator L terminal pin is probed at the generator with a test lamp to B+ the generator should charge the battery. Replace the generator if it is not charging.

Step	Action	Value(s)	Yes	No
1	Was the On-Board Diagnostic (OBD) System Check performed?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Turn ON the ignition leaving the engine OFF. Observe the IP battery light. Start the engine. Did the light turn OFF?	--	Go to Step 4	Go to Step 3
3	Check for a short to ground in the Generator Control/Monitoring circuit. Did you find a problem?	--	Go to Step 8	Go to Step 9
4	Measure the voltage at the generator output terminal on the generator with a J 39200 DMM. Did the meter indicate a voltage above the specified value?	12.6 V	Go to Step 5	Go to Step 6
5	View the IP voltmeter. Did the voltmeter indicate a value above the specified value?	12.6 V	Go to Diagnostic Aids	Go to Instrument Panel Cluster (IPC) System Check
6	Turn OFF the engine. Disconnect the generator harness connector. Probe the Generator Control/Monitoring circuit at the generator with a test lamp connected to the B+ terminal. Start the engine. Measure the voltage at the generator output terminal on the generator with a J 39200 DMM. Did the meter indicate a voltage above the specified value?	12.6 V	Go to Step 7	Go to Step 9
7	Check for an open or short to ground in the Generator Control/Monitoring circuit. Did you find a problem?	--	Go to Step 8	Go to Step 10
8	Repair the circuit as necessary. Refer to Wiring Repairs . Is the action complete?	--	Go to Step 11	--
9	Replace the generator. Refer to Generator Replacement 4.3L. Is the action Complete?	--	Go to Step 11	--
10	Replace the VCM. Program the new VCM. Refer to VCM Replacement/Programming . Perform the VTD Password Learn Procedure. Refer to Password Learn . Perform the CKP System Variation Learning Procedure. Refer to Crankshaft Position System Variation Learn . Is the action complete?	--	Go to Step 11	--
11	Operate the vehicle within the conditions under which the original symptom was noted. Does the system now operate properly?	--	System OK	Go to Step 1