8206noco.fm Page 198 Thursday, July 2, 1998 1:19 PM
SYMPTOM RELATED DIAGNOSTICS BUFFERED RPM (TACH DRIVE OUTPUT)
Figure 318 — Diagnostic Procedure Flowchart
Test 2 When performing electrical tests, it is important to wiggle wires and connectors to identify intermittent connection problems.
Checking for 12 volts and ground to tachometer 1. Turn the ignition key to the OFF position. 2. Disconnect the J1B connector from the V-MAC II module.
This diagnostic procedure starts from a customer complaint that the tachometer is not working.
3. Disconnect the tachometer connector. 4. Connect the serial link jumper into the serial communication port.
Checking for an external fault
5. On the harness side of the tachometer connector, check for 12 volts on the supply line.
1. Turn the ignition key to the OFF position.
6. Disconnect the serial link jumper.
2. Disconnect all external units at the buffered RPM external tie point (located near the accessory bus).
7. Check for continuity from the tachometer ground line to a good ground.
Test 1
3. Start the engine.
If the tachometer is now working, there is a short in the external harness or component. Locate and repair the short. Retest to be sure the problem has been corrected. If the tachometer still does not work, proceed to Test 2.
Page 198
If both supply and ground are present, proceed to Test 4. If 12-volt supply or ground are not present, locate and repair the missing supply or ground. Retest to be sure the problem has been corrected.
