AutoCodes – Lexus – P1123 Lexus

P1123 Lexus Code - Coolant Flow Control Valve Position Sensor Circuit High

Quick Answer

This system uses an electric pump to supply hot coolant stored in the heat storage tank into the cylinder head of the engine, in order to optimize engine starting combustion and reduce the amount of unburned gas that is discharged while the engine is started. Common causes include Coolant Flow Control Valve, Faulty Coolant Flow Control Valve Position Sensor, Coolant Flow Control Valve Position Sensor harness is open or shorted. 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: P1123 Lexus indicates Coolant Flow Control Valve Position Sensor Circuit High.
Common causes: Common causes include Coolant Flow Control Valve, Faulty Coolant Flow Control Valve Position Sensor, Coolant Flow Control Valve Position Sensor harness is open or shorted.
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 3,111

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Intermediate (2 / 3)

What is this?

Table of contents Created and updated by William Orellana on Dec 10, 2021

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code P1123 Lexus Description

This system uses an electric pump to supply hot coolant stored in the heat storage tank into the cylinder head of the engine, in order to optimize engine starting combustion and reduce the amount of unburned gas that is discharged while the engine is started. Before the engine starts, the Engine Control Module (ECM) operates the electric water pump to direct the hot coolant in the heat storage tank into the engine, in order to heat the cylinder head (this process is called preheat mode). The duration of the operation of the electric water pump is variable, depending on the temperature of the cylinder head. During the normal operation of the engine, the water valve opens the passage between the cylinder head and the heater and closes the passage between the cylinder head and the tank. During preheat mode in which the cylinder head is heated, the water valve opens the passage between the tank and the cylinder head, in order to allow the coolant to flow from the tank to the cylinder head. At this time, in order to warm up the intake port quickly before the engine is started, the coolant flows in the reverse direction.
The water valve for the Coolant Heat Storage (CHS) system, which is located at the heater hoses, controls the coolant passages to the engine, heater core, and the CHS tank in accordance with the operating conditions of the system.
The water valve consists of a water valve, valve position sensor, and valve control motor. The potentiometer, which is coupled coaxially to the water valve, converts the valve position into voltage and transmits it to the ECM in the form of a position signal.

OBDII Code P1123 Lexus - Coolant Flow Control Valve Position Sensor Circuit High - AutoCodes.com — P1123 Lexus Code - Coolant Flow Control Valve Position Sensor Circuit High

What does this mean?

What are the Possible Causes of the DTC P1123 Lexus?

Coolant Flow Control Valve
Faulty Coolant Flow Control Valve Position Sensor
Coolant Flow Control Valve Position Sensor harness is open or shorted
Coolant Flow Control Valve Position Sensor circuit poor electrical connection
Faulty Engine Control Module (ECM)

How to Fix the DTC P1123 Lexus?

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 P1123 Lexus 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 P1123 Lexus code?

Need more information on how to fix the P1123 Lexus code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the P1123 Lexus code diagnosed by a professional: Find a repair shop in your area

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 P1123 Lexus Code

1. What does the OBDII code P1123 mean on a Lexus?

P1123 indicates a problem with the Coolant Flow Control Valve Position Sensor Circuit, specifically a high voltage signal detected by the engine control module (ECM).

2. What are the common symptoms of code P1123 in a Lexus?

Symptoms may include an illuminated check engine light, inconsistent cabin heating, engine overheating, or reduced fuel efficiency.

3. What causes the P1123 code to appear on a Lexus?

Common causes include a faulty coolant flow control valve, damaged wiring or connectors in the sensor circuit, or a malfunctioning position sensor.

4. Can driving with the P1123 code damage my Lexus?

Driving with this code may lead to engine overheating or inefficient engine operation, which can cause long-term damage if not addressed promptly.

5. How can I diagnose the P1123 code on my Lexus?

Start by inspecting the coolant flow control valve, checking for damaged wiring or corroded connectors, and testing the position sensor for proper operation.

6. How do I fix the P1123 code on a Lexus?

Repairs may involve replacing the coolant flow control valve, repairing or replacing damaged wiring, or replacing the position sensor if it's faulty.

7. How much does it cost to fix the P1123 code on a Lexus?

Repair costs vary depending on the issue but typically range from $150 to $500, including parts and labor.

8. Can I reset the P1123 code without fixing the problem?

Resetting the code without addressing the root cause may temporarily clear the check engine light, but the code will likely return.

9. What tools are needed to diagnose and repair the P1123 code on a Lexus?

You'll need an OBDII scanner, a multimeter for electrical testing, and possibly basic hand tools to access and inspect components.

10. Is the P1123 code specific to Lexus vehicles?

While P1123 is a generic OBDII code, its description and troubleshooting steps are specific to Lexus models with a coolant flow control valve system.

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