B1872: Turn Signal Power Circuit High Voltage
The B1872 code indicates that the vehicle's control module (typically the Front Electronic Module or FEM in Ford vehicles) has detected an abnormally high voltage on the power supply circuit for the turn signals and hazard lights. This circuit provides positive current to the turn indicators and emergency flashers. A 'short to battery' means the power wiring is in direct contact with a constant positive voltage source, due to damaged insulation, a corroded connector, or an internal module failure. The FEM monitors this circuit and expects normal switching behavior; when it detects continuous voltage when it shouldn't be present, it logs this manufacturer-specific fault code.
1. Commonly Affected Makes
2. Most Common Causes
- Turn signal power circuit shorted to a battery wire or constant positive voltage circuit
- Damaged, crushed, or deteriorated insulation on the power circuit wiring or connector
- Defective turn signal relay or flasher with internally welded or stuck contacts
- Internal failure of the Front Electronic Module (FEM) or lighting control module
- Aftermarket electrical modifications (alarms, trailer wiring, accessories) with incorrect connections
- Corrosion in connectors causing bridging between power terminals
3. Symptoms You Will Notice
- Turn signals or hazard lights may be inoperative, stay on constantly, or flash rapidly
- Check Engine Light or warning indicator on the dashboard may illuminate
4. Step-by-Step Diagnosis
Scan the vehicle for all stored codes and note freeze frame data
Visually inspect the turn signal power circuit wiring and connectors for damage, corrosion, or shorts
Check the turn signal relay or flasher for proper operation and signs of welded contacts
Test for constant voltage on the power circuit with a multimeter when the signals are off
If wiring and relay are okay, suspect an internal FEM fault and perform module self-test or replacement
5. Frequently Asked Questions
Is it safe to drive?▼
Driving is possible but not recommended because inoperative or erratic turn signals and hazard lights pose a safety risk. Have the issue diagnosed and repaired promptly.
How much does it cost to fix?▼
Repair costs typically range from $100 to $400, depending on the cause. A simple wiring repair may cost $100-$200, while replacing the FEM can run $300-$800 including labor.