P1638 GMC Code - Generator 'F' Terminal Circuit Conditions
Quick Answer
The Powertrain Control Module (PCM) uses the generator field duty cycle signal circuit to monitor the duty cycle of the generator. 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
- P1638 GMC indicates Generator 'F' Terminal Circuit Conditions.
- 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.
Code P1638 GMC Description
The PCM monitors the state of the generator field duty cycle signal circuit. When the key is in the RUN position and the engine is OFF, the PCM should detect a duty cycle near 0 percent. However, when the engine is running, the duty cycle should be between 5-100 percent. The PCM monitors the PWM signal using a key ON test and a RUN test. During the tests, if the PCM detects an out of range PWM signal, DTC P1638 will set. When the DTC sets, the PCM will send a class 2 serial data message to the instrument panel cluster (IPC) to illuminate the charge indicator.
What are the Possible Causes of the DTC P1638 GMC?
- 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 P1638 GMC?
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 P1638 GMC 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.
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Frequently Asked Questions about P1638 GMC Code
1. What are the common symptoms of OBDII code P1638 GMC?
- Common symptoms include issues with the vehicle's charging system, such as a dead battery, dimming lights, or difficulty starting the engine.
2. What causes the OBDII code P1638 GMC to trigger?
- The code is typically triggered by faults in the generator 'F' terminal circuit, which may be caused by a faulty generator, damaged wiring, or poor electrical connections.
3. How can I diagnose the generator 'F' terminal circuit issues related to P1638 GMC?
- Use a multimeter to test the generator 'F' terminal for proper voltage output and check for any loose or damaged wiring connections.
4. Can a bad battery cause the OBDII code P1638 GMC to appear?
- Yes, a weak or failing battery can sometimes trigger this code due to its impact on the vehicle's electrical system and charging capabilities.
5. Are there any specific repair tips for fixing OBDII code P1638 GMC?
- Ensure that all wiring connections related to the generator 'F' terminal are secure and free of corrosion. Consider replacing the generator if it is found to be faulty.
6. Is it safe to continue driving with the OBDII code P1638 GMC present?
- It is not recommended to drive with this code active, as it may lead to further electrical system issues and potential stalling of the vehicle.
7. Can I reset the OBDII code P1638 GMC on my own?
- Yes, you can reset the code using an OBDII scanner or by disconnecting the vehicle's battery for a few minutes. However, it is important to address the underlying issue causing the code to prevent it from reoccurring.
8. How much does it typically cost to repair OBDII code P1638 GMC?
- The cost of repairs can vary depending on the specific issue causing the code, but it may range from around $100 for simple wiring repairs to $500 or more for a new generator.
9. Will OBDII code P1638 GMC affect my vehicle's performance?
- Yes, this code can affect the performance of your vehicle, especially in terms of its charging capabilities and overall electrical system functioning.
10. How urgent is it to address OBDII code P1638 GMC?
- It is important to address this code promptly to prevent potential damage to the vehicle's electrical system and ensure reliable operation of the charging system.
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