AutoCodes – Generic – P1637

P1637 Code - Generator L-Terminal Circuit

Quick Answer

The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and one destination) into the Powertrain Control Module (PCM). Common causes include Faulty Generator (Alternator), Generator harness is open or shorted, Generator circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: P1637 indicates Generator L-Terminal Circuit.
Common causes: Common causes include Faulty Generator (Alternator), Generator harness is open or shorted, Generator circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 34,959

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Sep 04, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1637 Description

The L-terminal circuit from the generator is a discrete circuit (a discrete circuit has no splices and only one source and one destination) into the Powertrain Control Module (PCM). The PCM applies ignition voltage to the generator L terminal circuit. A small amount of current flows from this circuit through the generator windings to create a magnetic field which starts the generator process. When the generator is at operating speed and producing voltage, a solid state switch for the L terminal circuit in the generator opens and the PCM detects that the initial startup current flow has stopped.
The PCM expects to detect low voltage on the L terminal circuit prior to the generator rotating at operating speed and conversely expects the circuit to be at ignition voltage potential when the generator is operational.

OBDII Code P1637 - Generator L-Terminal Circuit - AutoCodes.com — P1637 Code - Generator L-Terminal Circuit

What does this mean?

What are the Possible Causes of the DTC P1637?

Faulty Generator (Alternator)
Generator harness is open or shorted
Generator circuit poor electrical connection
Powertrain Control Module (PCM) programming
Faulty Powertrain Control Module (PCM)

How to Fix the DTC P1637?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the P1637 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the P1637 code?

Need more information on how to fix the P1637 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P1637 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

P1637 Audi — CAN Data Bus Electronic CE No Signal
P1637 Buick — Generator L-Terminal Circuit
P1637 Cadillac — Generator L-Terminal Circuit
P1637 Chevrolet — Generator L-Terminal Circuit
P1637 GMC — Generator L-Terminal Circuit
P1637 Mitsubishi — Malfunction of Memory Backup
P1637 Volkswagen — CAN Data Bus Electronic CE No Signal

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about P1637 Code

1. What are the common symptoms of OBDII code P1637 (Generator L-Terminal Circuit)?

The common symptoms of code P1637 include dim or flickering headlights, a dead battery, issues with electrical components, and the illumination of the battery light on the dashboard.

2. What are the possible causes of OBDII code P1637?

The possible causes of code P1637 include a faulty generator (alternator), damaged wiring or connectors in the generator circuit, a defective generator control module, or a weak battery.

3. How can I diagnose the Generator L-Terminal Circuit issue causing OBDII code P1637?

To diagnose the issue, you can start by checking the wiring and connectors in the generator circuit for any damage or corrosion. You can also test the generator output voltage and inspect the generator control module for any signs of malfunction.

4. Can I still drive my vehicle with OBDII code P1637 triggered?

It is not recommended to drive your vehicle with a triggered P1637 code, as it can lead to further electrical issues and potential stalling of the vehicle due to a failing generator.

5. How can I repair OBDII code P1637 on my own?

If you have experience with automotive electrical systems, you can attempt to repair the issue by replacing the faulty generator, repairing or replacing damaged wiring or connectors, or replacing the generator control module.

6. Will resetting the OBDII code P1637 make it go away permanently?

Resetting the code may temporarily clear the dashboard light, but if the underlying issue causing the code is not fixed, it is likely to reappear once the system detects the problem again.

7. Is it safe to continue driving if the battery light is illuminated along with code P1637?

Driving with the battery light on and code P1637 triggered is not recommended, as it indicates a potential issue with the charging system that can lead to a dead battery and loss of power while driving.

8. Can a P1637 code be caused by a weak battery?

Yes, a weak or failing battery can sometimes trigger the P1637 code, as the charging system may be working harder to compensate for the battery's lack of power, leading to issues with the generator circuit.

9. How much does it typically cost to repair OBDII code P1637 at a professional repair shop?

The cost of repairing code P1637 can vary depending on the underlying issue, but it may range from $200 to $600 at a professional repair shop, including parts and labor.

10. Can OBDII code P1637 affect the performance of my vehicle?

Yes, code P1637 can affect the performance of your vehicle, especially if it leads to a failing generator or charging system, which can result in electrical issues, stalling, and difficulty starting the vehicle.