AutoCodes – Cadillac – P1642 Cadillac

P1642 Cadillac Code - Fan Control Relay 2 and 3 Control Circuit

Quick Answer

Ignition voltage is supplied to the Cooling Fan relay coil. Common causes include Faulty Cooling Fan Relay, Cooling Fan Relay harness is open or shorted, Cooling Fan Relay circuit poor electrical component. 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: P1642 Cadillac indicates Fan Control Relay 2 and 3 Control Circuit.
Common causes: Common causes include Faulty Cooling Fan Relay, Cooling Fan Relay harness is open or shorted, Cooling Fan Relay circuit poor electrical component.
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 3,859

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 P1642 Cadillac Description

Ignition voltage is supplied to the Cooling Fan relay coil. The Powertrain Control Module (PCM) controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be low (near 0 volts). When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high (near battery voltage). If the fault detection circuit senses a voltage other than what is expected, the fault line status will change causing the code to set.
The relay is used to control the high current flow to the cooling fan motors. This allows the PCM driver to only have to handle the relatively low current used by the relay.

OBDII Code P1642 Cadillac - Fan Control Relay 2 and 3 Control Circuit - AutoCodes.com — P1642 Cadillac Code - Fan Control Relay 2 and 3 Control Circuit

What does this mean?

What are the Possible Causes of the DTC P1642 Cadillac?

Faulty Cooling Fan Relay
Cooling Fan Relay harness is open or shorted
Cooling Fan Relay circuit poor electrical component

How to Fix the DTC P1642 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 P1642 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.