P1199 Radiator Temperature Sensor Voltage Too Low

The “P1199 Radiator Temperature Sensor Voltage Too Low Code” is an OBD-II diagnostic trouble code that appears when the Engine Control Module (ECM) detects an unusually low voltage reading from the radiator temperature sensor.

By continuously measuring the coolant temperature, the sensor assists the ECM in regulating the engine’s operating temperature within the optimal range. In this article I am going to explain why this code appears and how to fix it smoothly.

A radiator temperature sensor voltage that is too low indicates that your car’s cooling system is not operating properly.

This can be caused by a faulty thermostat, an insufficient coolant level, or an electrical fault in the radiator temperature sensor itself. To fix this problem, you should first check the coolant level and add more as needed.

Understanding The P1199 Error Code

The P1199 code specifically points to an issue where the voltage signal from the radiator temperature sensor falls below a predetermined threshold.

Can indicate a malfunction or deterioration in either the sensor itself, the wiring connecting it to the ECM, or even potential problems with the ECM’s ability to interpret the sensor’s signals accurately.

When the ECM receives a voltage reading that is too low from the radiator temperature sensor, it triggers the P1199 code and typically illuminates the Check Engine Light on the vehicle’s dashboard.

Ignoring this code and its underlying issue can lead to various problems, such as engine overheating, reduced fuel efficiency, and potential long-term damage to the engine components.

Effectively diagnosing and resolving the P1199 error code is essential for maintaining proper engine performance, preventing engine damage, and ensuring the vehicle operates at its optimal efficiency.

What is the Radiator Temperature Sensor?

P1199 Radiator Temperature Sensor Voltage Too Low

The Radiator Temperature Sensor, also known as the Engine Coolant Temperature (ECT) sensor or Coolant Temperature Sensor (CTS), is a vital component within a vehicle’s engine management system.

Its primary function is to monitor and provide real-time feedback on the temperature of the engine coolant. This information is critical for maintaining the engine’s operating temperature within a safe and efficient range.

The sensor is typically located in or near the engine’s cooling system, often attached to the engine block, cylinder head, or in close proximity to the radiator.

It’s exposed to the circulating coolant, allowing it to accurately measure the temperature fluctuations as the engine operates.

Also Read: P1283 Idle Select Signal Invalid

Symptoms of a P1199 Error Code

Reduced Fuel Efficiency:

A malfunctioning Radiator Temperature Sensor can cause the engine to operate in suboptimal conditions, which may result in decreased fuel efficiency.

If the ECM doesn’t receive accurate temperature data, it might not adjust the air-fuel mixture optimally, leading to increased fuel consumption.

Check Engine Light Illumination:

When the ECM detects a low voltage reading from the Radiator Temperature Sensor, it triggers the P1199 error code and illuminates the check engine light on the dashboard. This serves as an indicator to the driver that something is amiss within the cooling system or engine management.

Poor Performance:

The inaccurate temperature readings caused by the low voltage condition can lead to compromised engine performance.

You might notice sluggish acceleration, reduced power output, and a general lack of responsiveness from the engine.

Erratic Cooling Fan Operation:

The cooling fans, which help regulate engine temperature, may exhibit irregular behavior. They might turn on more frequently than usual or fail to engage when needed, leading to potential overheating concerns.

Fluctuating Temperature Gauge:

If your vehicle has a temperature gauge on the dashboard, you might notice erratic temperature readings or fluctuations that don’t align with the actual engine conditions. This can be a sign of the sensor’s inaccurate voltage readings.

Difficulty Starting the Engine:

In extreme cases, the low voltage condition might affect the engine’s ability to start smoothly. If the ECM is receiving inconsistent temperature data, it could disrupt the engine’s starting process.

Causes of a Low Radiator Temperature Sensor Voltage

Here are some common culprits that can lead to a low Radiator Temperature Sensor voltage:

Faulty Radiator Temperature Sensor:

Causes of a Low Radiator Temperature Sensor Voltage

Over time, sensors can degrade or malfunction due to wear and tear. A malfunctioning sensor might not provide accurate voltage readings, leading to the P1199 code. This could be due to internal component failure or damage caused by exposure to extreme temperatures.

Wiring Issues:

Damaged or corroded wiring connecting the Radiator Temperature Sensor to the Engine Control Module (ECM) can disrupt the voltage signal. Frayed, broken, or corroded wires can cause intermittent or low voltage readings, triggering the P1199 code.

Poor Electrical Connections:

Loose or poor electrical connections at the sensor or within the wiring harness can result in voltage irregularities. These connections may become compromised over time due to vibrations, exposure to the elements, or improper installation.

ECM Malfunction:

The Engine Control Module (ECM) interprets the voltage signals from various sensors, including the Radiator Temperature Sensor.

If the ECM itself is malfunctioning, it might misinterpret the sensor’s signals, leading to erroneous codes like P1199.

Coolant Leakage or Air Bubbles:

A low coolant level, air bubbles trapped in the cooling system, or improper coolant mixture can affect the sensor’s ability to accurately measure temperature. Inaccurate coolant readings can result in erroneous voltage signals.

Coolant Temperature Sensor Circuit Issues:

Apart from the sensor itself, issues within the sensor circuit can lead to low voltage readings. This can include issues with ground connections, short circuits, or open circuits.

Faulty Cooling Fans:

Cooling fans help regulate engine temperature. If the cooling fans are malfunctioning, the engine might run hotter than usual, causing the Radiator Temperature Sensor to detect lower temperatures than expected.

Also Read: P1194 Incorrect Or Irrational Performance Has Been Detected For The Pwm

How To Fix P1199 Fault Code: Step By Step Process

P1199 Radiator Temperature Sensor Voltage Too Low

Check for Symptoms:

Start by identifying any symptoms associated with the P1199 code, such as engine overheating, poor performance, or illuminated Check Engine Light. This will provide context for your diagnostic process.

Use OBD-II Scanner:

Connect the OBD-II scanner to the vehicle’s OBD-II port (usually located beneath the dashboard near the driver’s seat). Retrieve the diagnostic trouble codes (DTCs), including the P1199 code.

Note down any freeze frame data, which provides information about the conditions under which the code was triggered.

Inspect Radiator Temperature Sensor:

Locate the Radiator Temperature Sensor. Refer to the vehicle’s repair manual if needed. Check the sensor’s wiring and connector for any signs of damage, corrosion, or loose connections. Repair or replace as necessary.

Test the Sensor’s Voltage:

With the engine off, use a multimeter to measure the voltage output of the Radiator Temperature Sensor. Compare the measured voltage with the manufacturer’s specifications for the sensor. If the voltage is significantly lower than the specified range, the sensor may be faulty and require replacement.

Inspect Wiring and Connections:

Inspect the wiring harness connected to the Radiator Temperature Sensor for any visible damage, fraying, or breaks. Check the ground connection to ensure it’s securely connected to the engine block.

Check Cooling System:

Inspect the coolant level in the radiator and reservoir. Low coolant levels can affect the sensor’s accuracy. Look for any signs of coolant leakage that might be affecting the sensor’s readings.

Test Cooling Fan Operation:

Ensure the cooling fans are operating properly. Run the engine and observe if the cooling fans engage when the engine reaches operating temperature. A malfunctioning cooling fan system can lead to inaccurate temperature readings.

Diagnose ECM and Circuit Issues:

If all previous steps don’t reveal the issue, it might be necessary to diagnose potential ECM or circuit problems. Consult the vehicle’s repair manual or seek professional assistance for these advanced diagnostics.

Clear DTCs and Test:

If you’ve replaced or repaired any components, clear the DTCs using the OBD-II scanner. Test-drive the vehicle to ensure that symptoms have been resolved and the Check Engine Light remains off.

Frequently Asked Questions

1. What does the P1199 error code mean?

The P1199 error code signifies that the Radiator Temperature Sensor Voltage is Too Low.

2. What symptoms might I experience if my vehicle triggers the P1199 code?

Symptoms of the P1199 code include engine overheating, reduced fuel efficiency, and an illuminated Check Engine Light.

3. Can I continue driving with the P1199 code activated?

It’s not advisable to continue driving with the P1199 code activated, as it can lead to engine issues and damage.

4. Can I diagnose and fix the P1199 code myself?

While DIY diagnosis and repair are possible, seeking professional help is recommended for accurate resolution.

5. Is the P1199 code specific to certain vehicle makes and models?

The P1199 code is a standardized OBD-II code, present in various vehicle makes and models.

Ect Sensor

If you’re in the market for a reliable and accurate engine monitoring system, then an ECT Sensor could be the perfect solution.

An ECT Sensor (also known as an Engine Coolant Temperature Sensor) is a device used to measure the temperature of a vehicle’s coolant fluid.

This information can be used by your car’s computer to adjust fuel/air mixture and ignition timing, ensuring optimal performance and efficiency.

The ECT sensor works by measuring the electrical resistance between two terminals on its body. As coolant flows through the sensor, it causes changes in that resistance which are picked up by the computer and translated into actual temperature readings.

One of the primary benefits of using an ECT sensor is that it allows for more precise control over how much gasoline is burned at any given time according to current operating conditions.

By accurately gauging how hot or cold your engine’s running environment is, your car can adjust its fuel injection rate accordingly – resulting in both improved performance and economy when compared to traditional carburetor systems.

What is the P1199 Radiator Temperature Sensor Voltage Too Low Code

If your car’s check engine light is on, it can cause an alarm. But the problem could be something minor, like a faulty sensor or component. One such diagnostic trouble code that may appear is P1199 Radiator Temperature Sensor Voltage Too Low.

This sensor helps regulate coolant flow and engine temperature by sending readings back to the computer so that adjustments can be made as needed.

If there’s not enough voltage from this sensor, then there won’t be accurate readings coming back to the computer – resulting in either too much or too little cooling taking place in relation to actual conditions.

How Can I Tell If My Vehicle Has a Low Radiator Temperature Sensor Voltage

If you suspect that your car has a low voltage reading from its radiator temperature sensor, there are a few ways you can check and diagnose it.

First off, if your car has an onboard diagnostic system (OBD), you should check for any trouble codes related to the cooling system or engine temperature.

These codes may provide information about what is causing the low voltage reading. Additionally, testing the resistance of the sensor itself will help determine whether or not it is functioning properly.

A faulty sensor could result in inaccurate readings which would lead to incorrect temperatures being reported by your car’s computer system.

What Causes the P1199 Radiator Temperature Sensor Voltage Too Low Code to Be Triggered

The radiator temperature sensor is designed specifically to measure the temperature of the coolant contained within your vehicle’s cooling system.

This data is relayed back to the engine control unit (ECU) which then uses it to adjust things like ignition timing and fuel injection accordingly so that your engine can run at its optimal performance level while keeping temperatures safe.

When this particular trouble code is activated, however, it means that something has gone wrong with either the sensor itself or one of its associated components—which can range from wiring issues all the way up to an ECU malfunction.


As the P1199 Radiator Temperature Sensor Voltage Too Low Code code flashes on the digital dashboard, it unveils that your radiator isn’t working efficiently as it is supposed to.

In this article I have journeyed into the realms of potential problems, symptoms, and causes and how to fix the issue all by yourself.

And so, as you stand at the crossroads of the P1199 code, remember that this code speaks a language of caution, urging you to delve into the heart of your vehicle’s health.