Fault code P00B6 – radiator coolant temperature/engine coolant temperature correlation

Fault code P00B6 is called “Radiator Coolant Temperature (CTS)/Engine Coolant Temperature (ECT) Correlation” but in different programs it may be called differently. This fault designation applies to all vehicles equipped with OBD-II.

Technical description and explained code P00B6

If you encounter code P00B6 during diagnosis, it means that the powertrain control module (PCM) has detected a mismatch in the correlated signals. The mismatch is between the radiator coolant temperature sensor (CTS) and the engine coolant temperature sensor (ECT).

To ensure that the coolant flows properly between the radiator and the engine cooling ducts. The coolant temperature in the radiator is monitored compared to the coolant temperature in the engine.

The ECT sensor design usually consists of a thermistor immersed in solid resin and housed in a metal or plastic housing. The most popular housing material is brass because of its durability.

The level of thermal resistance in the ECT sensor decreases as the coolant heats up and flows through it. This causes the ECT sensor circuit voltage to increase, after which data is sent to the PCM.

As the engine cools, the sensor resistance increases and as a result the ECT sensor circuit voltage decreases. The PCM recognizes these voltage variations as changes in engine coolant temperature.

The coolant temperature sensor in the radiator monitors coolant temperature in much the same way as the engine temperature sensor. It is usually plugged into one of the radiator tanks, but can also be installed in a pressurized coolant reservoir.

If the PCM detects voltage signals from the ECT sensor and the radiator coolant temperature sensor that differ from each other more than the maximum allowable parameter. Then code P00B6 will be stored and the Malfunction Indicator Light (MIL) may illuminate.

It may take several fault cycles with incorrect data to activate the MIL indication.

Symptoms of vehicle malfunctions

The main signal that an error P00B6 has occurred is the Malfunction Indicator Lamp (MIL) is also known as the CheckEngine Light.

It can also be warning signs such as:

1. Check engine control lamp on the control panel will light up (the code will be recorded in the memory as a malfunction).
2. The engine stalls or starts badly (especially when starting cold).
3. Floating revolutions, as well as attempts to stall at idle.
4. Overheating of the vehicle engine.
5. Incorrect or false temperature readings.
6. Increased fuel consumption.
7. Black smoke coming out of the exhaust pipe, if the mixture is rich.
8. Increased NOx emissions may be seen with lean mixture.
9. Abnormal operation of the cooling fans.

Error P00B6 is not a serious error, the car will be able to start and continue driving. But it’s better to solve it as soon as possible, because improper heat exchange can lead to more serious consequences.

Factors that can cause this error code

The error code P00B6 can mean that one or more of the following problems have occurred:

• The radiator coolant temperature sensor (CTS) has failed.
• Defective engine coolant temperature sensor (ECT).
• Contamination of the sensors.
• Coolant temperature sensor circuit is broken.
• The wiring harness or connector for the coolant temperature sensors is damaged.
• Blown fuse.
• Insufficient coolant level.
• Sometimes the cause is a faulty PCM module.

How to fix or reset OBD-2 code P00B6

Some suggested steps for troubleshooting and fix the error code P00B6:

1. Read all stored data and error codes with an OBD-II scan tool. To find out when and under what circumstances error P00B6 appeared.
2. Clear the error codes from the computer memory and test-drive the vehicle to find out if error P00B6 appears again.
3. Check the coolant level (engine should be cold).
4. Visually inspect the electrical wiring and connections to the coolant temperature sensors for looseness or damage. Repair as necessary.
5. If the CTS or ECT sensor has failed, replace it.
6. Inspect the fuse, if it is blown, replace it.
7. Clear the error code from the computer memory again, and test-drive the vehicle to see if the problem is resolved.

Diagnose and repair of problems

The first step in troubleshooting error P00B6, is to review the technical service bulletins (TSB). For known problems with a particular vehicle.

Perform a thorough visual inspection to check the wiring for obvious defects such as scratches, scuffs, exposed wires or burn spots. Next, check connectors and connections for safety, corrosion, and contact damage.

Be sure to carefully check the integrity of the wire harnesses and secure any loose wires. If you find a burned wire, solder it and make sure it is properly insulated.

Check coolant and thermostat

Make sure the coolant level is correct, both in the radiator (when cold) and in the coolant overflow tank. Make sure that there are no leaks and that the sealed cap is working properly.

If there is not enough coolant in the system, the engine may not warm up properly. Because if the temperature sensor is not in contact with the coolant, it will not read the temperature.

Using a non-contact thermometer, or a real-time streaming scan tool, check to see if the engine is warming up properly. Normally, the upper radiator hose should stay relatively cold until the thermostat opens. After that, it will warm up quickly.

If the thermostat is open, the coolant will leak constantly, preventing the engine from reaching operating temperature. This can also be the cause of fault code P00B6.

Use a thermometer or diagnostic tool to check the engine temperature after 10-15 minutes of operation. If the temperature does not reach the operating temperature, check the CTS sensor.

Check the CTS and ECT sensors

Visually check the sensors for damaged wiring or connectors and repair if necessary. Then connect an OBD2 scanner, if the radiator temperature is excessively high, about 284°F, this is not normal.

Disconnect the sensors and see if the reading drops, like 50°F. If it does, the sensor is probably faulty, shorted internally, causing a low resistance signal to be sent to the PCM.

But, if you want to be completely sure it’s the sensor and not the wiring, you can do a test. Check the resistance of the sensor against ground with an ohmmeter. The resistance of a normal sensor will vary slightly from car to car.

But basically, if the engine temperature is about 200 degrees Fahrenheit, the resistance will be about 200 ohms. At temperatures around 0°F, the resistance will be over 10,000 ohms.

With this test, you will be able to determine if the resistance of the sensor matches the temperature in the system. If it doesn’t match the radiator temperature, you probably have a faulty sensor.

On which vehicles does this problem occur most frequently

Fault code P00B6 can occur on different vehicles but there are statistics on which brands this occurs most often. Here is a list of some of them:

• Chevrolet (Aveo, Cruze, Express)
• Opel (Corsa, Insignia)
• Volkswagen (Polo)

Fault code P00B6 can sometimes be found with other errors. The most common are the following: P00B1, P00B2, P00B3, P00B4, P00B5.

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