AutoCodes – Buick – P2603 Buick

P2603 Buick Code - Auxiliary Coolant Pump Circuit High

Quick Answer

The auxiliary coolant pump and cooling fan system provides a measure of prevention against fuel vaporization due to excessive engine temperatures. Common causes include Faulty Auxiliary Coolant Pump Relay, Blocked pump control passage, Faulty Auxiliary Coolant Pump. 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: P2603 Buick indicates Auxiliary Coolant Pump Circuit High.
Common causes: Common causes include Faulty Auxiliary Coolant Pump Relay, Blocked pump control passage, Faulty Auxiliary Coolant Pump.
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 1,210

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 Jan 19, 2019

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P2603 Buick Description

The auxiliary coolant pump and cooling fan system provides a measure of prevention against fuel vaporization due to excessive engine temperatures. The Engine Control Module (ECM) commands the auxiliary or after boil coolant pump ON when the engine coolant temperature exceeds a calibrated value after engine shut down. The ECM applies ground to the coil side of the auxiliary pump relay. This energizes the coil and applies voltage directly to the pump motor through the switch side of the relay. When the auxiliary coolant pump is activated, coolant is drawn from radiator and pumped into the engine through a tee in the engine coolant inlet pipe. As the colder temperature coolant is drawn into the engine warmer coolant is expelled from the engine and back to the radiator. Removing high temperature coolant from the engine after shut down helps prevent vaporization of the fuel that remains in the fuel injectors and fuel rail during a hot soak.

OBDII Code P2603 Buick - Auxiliary Coolant Pump Circuit High - AutoCodes.com — P2603 Buick Code - Auxiliary Coolant Pump Circuit High

What does this mean?

What are the Possible Causes of the DTC P2603 Buick?

Faulty Auxiliary Coolant Pump Relay
Blocked pump control passage
Faulty Auxiliary Coolant Pump
Auxiliary Coolant Pump harness is open or shorted
Auxiliary Coolant Pump circuit poor electrical connection

How to Fix the DTC P2603 Buick?

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 P2603 Buick 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.

Frequently Asked Questions about P2603 Buick Code

1. What does the OBDII code P2603 Buick indicate?

The P2603 Buick code indicates a problem with the auxiliary coolant pump circuit, specifically that the circuit voltage is higher than expected. This could mean there is an electrical issue such as a short to power.

2. What are common symptoms of the P2603 Buick code?

Symptoms may include overheating of the engine, the auxiliary coolant pump not operating, an illuminated check engine light, and possibly reduced engine performance if the vehicle enters a protective mode.

3. What can cause the P2603 code to appear in a Buick?

Causes for the P2603 code can include a faulty auxiliary coolant pump, damaged wiring or connectors in the pump circuit, or a problem with the engine control module (ECM) providing incorrect signals.

4. How is the P2603 Buick code diagnosed?

Diagnosis involves using a scan tool to read the fault code and examining the auxiliary coolant pump and its circuitry. This includes checking for damaged wires, testing voltage levels, and ensuring connectors are secure and not corroded.

5. What repairs can fix the P2603 code?

Repairs might include replacing the auxiliary coolant pump, repairing or replacing damaged wiring or connectors, or in some cases, replacing or reprogramming the engine control module.

6. Is it safe to drive a Buick with the P2603 code?

Driving with the P2603 code can lead to engine overheating and should be avoided. It is advisable to address the issue promptly to prevent potential engine damage.

7. How urgent is it to address a P2603 Buick code?

It is fairly urgent to address the P2603 code because continuing to drive with an ineffective coolant system can lead to engine overheating and more severe engine damage.

8. Could the P2603 Buick code affect the vehicle's fuel economy?

Yes, if the engine is overheating or if the ECM places the engine in a protective mode, it can affect the vehicle's overall performance and fuel efficiency.

9. What tools are needed to diagnose the P2603 Buick code?

Tools needed for diagnosis may include a digital multimeter, a scan tool, and basic hand tools to access the auxiliary coolant pump and wiring.

10. Are there any preventive measures to avoid the P2603 code in Buicks?

Regular maintenance of the cooling system, including periodic checks of the coolant levels, pump operation, and inspection of wiring and connectors, can help prevent issues related to the P2603 code.