Generator L-Terminal Circuit
2004-2007 Buick Rainier 4.2L I6
Description
The PCM detected a fault on the generator (alternator) L-terminal circuit. The PCM applies ignition voltage to the L-terminal to initiate generator operation. When the generator reaches operating speed, the L-terminal current stops. The PCM monitors this circuit for opens and shorts. Note: The MIL will NOT illuminate for this code (non-emissions DTC).
Symptoms
- Battery warning light on dashboard
- Dim or flickering headlights
- Battery draining
- Electrical system issues
- Difficulty starting
Common Causes
- Faulty generator/alternator (internal regulator)
- Open or shorted L-terminal wiring
- Non-OEM aftermarket alternator not communicating properly
- Corroded connector
- PCM failure (rare)
Diagnostic Steps
- Test generator output voltage and current
- Inspect L-terminal wiring from generator to PCM
- Check for proper voltage on L-terminal (low with key on/engine off, ignition voltage when running)
- Test with OEM alternator if aftermarket is installed
- Inspect connector for corrosion
Repair Notes
Test alternator output. If using aftermarket alternator, verify it communicates the 5V reference properly (OEM alternators recommended). Check L-terminal wiring.
Related Codes
Other Powertrain Codes
- P0001Fuel Volume Regulator Control Circuit/Open
- P0002Fuel Volume Regulator Control Circuit Range/Performance
- P0003Fuel Volume Regulator Control Circuit Low
- P0004Fuel Volume Regulator Control Circuit High
- P0010Intake Camshaft Position Actuator Circuit/Open Bank 1
- P0011Intake Camshaft Position Timing Over-Advanced Bank 1
- P0012Intake Camshaft Position Timing Over-Retarded Bank 1
- P0013Exhaust Camshaft Position Actuator Circuit/Open Bank 1
- P0014Exhaust Camshaft Position Timing Over-Advanced Bank 1
- P0015Exhaust Camshaft Position Timing Over-Retarded Bank 1
P1637 on Other Vehicles
Common Questions
What does code P1637 mean on a 2004-2007 Buick Rainier?
P1637 stands for "Generator L-Terminal Circuit". The PCM detected a fault on the generator (alternator) L-terminal circuit. The PCM applies ignition voltage to the L-terminal to initiate generator operation. When the generator reaches operating speed, the L-terminal current stops. The PCM monitors this circuit for opens and shorts. Note: The MIL will NOT illuminate for this code (non-emissions DTC).
What are the symptoms of P1637 on a Buick Rainier?
Common symptoms of P1637 include: Battery warning light on dashboard, Dim or flickering headlights, Battery draining, Electrical system issues, Difficulty starting.
What causes P1637 on a 2004-2007 Buick Rainier?
Common causes of P1637 include: Faulty generator/alternator (internal regulator), Open or shorted L-terminal wiring, Non-OEM aftermarket alternator not communicating properly, Corroded connector, PCM failure (rare).