Applicable Systems
OBD-II
Symptoms
Alternator field terminal signal high; ECM detects field circuit short to +V; alternator may overcharge.
Possible Causes
- Field wire short to +12V
- Alternator internal field circuit failure
- ECM field driver shorted high
Troubleshooting Steps
- Step 1: Check field terminal for short to +12V
No short - Step 2: Check field wiring for chafing to +12V
No chafing - Step 3: Replace alternator if internal fault
New alternator normal - Step 4: Clear code and verify charging voltage
Voltage 13.8-14.4V
How to Reset
Clear with OBD-II scanner after repair.
Common Replacement Parts
- Alternator (OEM spec)
Frequently Asked Questions
- Q: Can field circuit cause overcharging?
Yes. If field circuit is shorted to +12V, alternator goes to full field (maximum output), causing overcharging and battery damage.
Source: SAE J2012 standard DTC list + OBD-II portal
Category: OBD-II