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Engine-Codes – GMC – P1538 GMC

P1538 GMC Code - A/C Request Circuit High Voltage

Quick Answer

The P1538 GMC diagnostic trouble code (DTC) indicates a problem with the A/C request circuit having high voltage. Common causes include Faulty A/C request circuit wiring, Defective A/C request circuit sensor, ECM software issue. Severity is Low - monitor the vehicle and repair when practical. The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.

What it means
P1538 GMC indicates A/C Request Circuit High Voltage.
Common causes
Common causes include Faulty A/C request circuit wiring, Defective A/C request circuit sensor, ECM software issue.
Severity
Low - monitor the vehicle and repair when practical.
Can I drive?
The vehicle can usually be driven if no severe symptoms are present, but symptoms should be checked before extended driving.
What is this?
Table of contents Created and updated by William Orellana on Sep 10, 2024
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Code P1538 GMC Description

The P1538 GMC diagnostic trouble code (DTC) indicates a problem with the A/C request circuit having high voltage. This code is specific to GMC vehicles and is typically related to issues within the air conditioning system. The A/C request circuit is responsible for sending signals to the vehicle's engine control module (ECM) to activate the air conditioning compressor when the A/C system is turned on.

OBDII Code P1538 GMC - A/C Request Circuit High Voltage
P1538 GMC Code - A/C Request Circuit High Voltage

Common Causes of P1538 GMC

  1. Faulty A/C request circuit wiring
  2. Defective A/C request circuit sensor
  3. ECM software issue
  4. Electrical short or open circuit in the A/C request circuit
  5. Incorrect refrigerant pressure

Symptoms of P1538 GMC

  1. Air conditioning system not cooling effectively
  2. A/C compressor cycling on and off frequently
  3. A/C compressor not engaging at all
  4. Check Engine Light illuminated
  5. Decreased fuel efficiency

How to Fix P1538 GMC

  1. Perform a thorough inspection of the A/C request circuit wiring and connectors for any signs of damage or corrosion. Repair or replace any damaged wiring or connectors.
  2. Test the A/C request circuit sensor to ensure it is functioning correctly. Replace the sensor if necessary.
  3. Check for any software updates for the ECM related to the A/C system. Update the ECM software if needed.
  4. Test the A/C system for correct refrigerant pressure and recharge the system if necessary.
  5. Clear the DTC and reset the ECM to see if the issue persists. If the code returns, further diagnostics may be needed to pinpoint the exact cause of the high voltage in the A/C request circuit.

Cost to Fix P1538 GMC

The cost of repairing a P1538 GMC code can vary depending on the specific cause of the issue. On average, you can expect to pay anywhere from $100 to $500 for parts and labor. It's important to note that diagnostic time and labor rates at auto repair shops can vary, so it's best to get a quote from a trusted mechanic before proceeding with the repair. Additionally, the cost may also be influenced by the location, make and model of the vehicle, and the type of engine.

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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 P1538 GMC Code

1. What does the OBDII code P1538 mean on a GMC vehicle?

P1538 indicates a problem with the A/C Request Circuit, specifically high voltage detected in the circuit.

2. What are the common symptoms of code P1538 in a GMC?

Symptoms may include the A/C system not engaging, reduced cooling performance, and the check engine light illuminated.

3. What causes the P1538 code to appear?

Common causes include a faulty A/C request switch, damaged wiring or connectors in the A/C circuit, or issues with the HVAC control module.

4. Can I still drive my GMC with a P1538 code?

Yes, but the A/C system may not function properly, which could affect comfort in hot weather.

5. How do I diagnose the P1538 code on my GMC?

Use a scan tool to confirm the code, inspect the A/C request switch, wiring, and connectors for damage, and test circuit voltage.

6. What repairs can fix the P1538 code?

Repairs may include replacing the A/C request switch, repairing or replacing damaged wiring or connectors, or recalibrating the HVAC control module.

7. Is the P1538 code related to the vehicle’s engine performance?

No, P1538 specifically pertains to the A/C system and does not directly affect engine performance.

8. How much does it cost to fix the P1538 code on a GMC?

Costs vary depending on the issue but typically range from $100 to $300 for diagnosis and repair.

9. Can a blown fuse cause the P1538 code?

Yes, a blown fuse in the A/C system circuit can cause high voltage issues and trigger this code.

10. Should the A/C system be recharged if code P1538 appears?

Recharging the A/C system may not resolve this code unless the issue is directly related to refrigerant pressure affecting the circuit.

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