P1638 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 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 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?
- 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?
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 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 P1638 code?
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Need Help with the Code?
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Information for Specific Makes
- P1638 BMW — Throttle Valve Position Control Throttle Stuck Temporarily
- P1638 Buick — Generator 'F' Terminal Circuit Conditions
- P1638 Cadillac — Generator 'F' Terminal Circuit Conditions
- P1638 Chevrolet — Generator 'F' Terminal Circuit Conditions
- P1638 GMC — Generator 'F' Terminal Circuit Conditions
- P1638 Hyundai — Engine Control Module Malfunction
- P1638 MINI — Throttle Valve Position Control Throttle Stuck Temporarily
Frequently Asked Questions about P1638 Code
No Frequently Asked Questions about P1638 Code found.
Discuss the causes and fixes for P1638 OBDII Code
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I checked the alternator, noticed a black substance melted by the front pulley and droppings on the block.Customer had it replaced before.
I hope this helps
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