Applicable Systems
EMCP 4.2
Symptoms
Alternator output current fluctuating; charging system unstable; battery may not maintain charge under load.
Possible Causes
- Alternator diode failure
- Alternator belt slipping
- Battery with shorted cell
Troubleshooting Steps
- Step 1: Check alternator belt tension and condition
Belt tight, no glazing - Step 2: Measure alternator AC ripple (should be < 0.5V AC)
AC ripple < 0.5V - Step 3: Test battery with conductance tester
Battery passes load test - Step 4: Check alternator output under load (lights, AC, blower on)
Output stable under load - Step 5: Replace alternator if AC ripple high
Output stable, no ripple
How to Reset
Clear via Cat ET after alternator service.
Common Replacement Parts
- Alternator P/N: 328-3924
Frequently Asked Questions
- Q: What is alternator AC ripple?
Small AC voltage superimposed on DC output. High ripple indicates bad diodes in alternator rectifier. Can cause electrical system issues and ECM faults.
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Source: caterpillarfaultcodes.com CID list
Category: Heavy Equipment
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