AutoCodes – Cadillac – P1639 Cadillac

P1639 Cadillac Code - PCM 5 Volt Reference Voltage Circuit Condition

Quick Answer

The Powertrain Control Module (PCM) uses the 5-volt reference 2 circuit as a sensor feed for the A/C refrigerant pressure sensor. Common causes include Sensor using 5 volt reference line shorted to ground, Circuit short to ground. 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: P1639 Cadillac indicates PCM 5 Volt Reference Voltage Circuit Condition.
Common causes: Common causes include Sensor using 5 volt reference line shorted to ground, Circuit short to ground.
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 8,240

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
Comments
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Code P1639 Cadillac Description

The Powertrain Control Module (PCM) uses the 5-volt reference 2 circuit as a sensor feed for the A/C refrigerant pressure sensor. The PCM monitors the voltage on the 5-volt reference 2 circuit.

OBDII Code P1639 Cadillac - PCM 5 Volt Reference Voltage Circuit Condition - AutoCodes.com — P1639 Cadillac Code - PCM 5 Volt Reference Voltage Circuit Condition

What does this mean?

What are the Possible Causes of the DTC P1639 Cadillac?

Sensor using 5 volt reference line shorted to ground
Circuit short to ground

How to Fix the DTC P1639 Cadillac?

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 P1639 Cadillac 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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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.