P00B6 Radiator Coolant Temperature / Engine Coolant Temperature Correlation

P00B6 Radiator Coolant Temperature / Engine Coolant Temperature Correlation

OBD-II DTC Datasheet

Correlation between radiator coolant temperature and engine coolant temperature

What does this mean?

This Generic Powertrain Diagnostic Trouble Code (DTC) is commonly applied to many OBD-II vehicles. This may include many automakers, but oddly enough, this DTC seems to be more common on Chevrolet / Chevy and Vauxhall vehicles.

Every time I came across a P00B6 diagnostic, it meant that the powertrain control module (PCM) detected a mismatch in the correlated signals between the radiator coolant temperature sensor and the engine coolant temperature (ECT) sensor.

To ensure that the coolant flows properly between the radiator and the engine cooling passages, the temperature of the coolant in the radiator is sometimes monitored against the temperature of the coolant in the engine.

The ECT sensor design typically consists of a thermistor immersed in hard resin and housed in a metal or plastic case. Brass is the most popular of these body materials due to its durability. In most cases, the ECT sensor is threaded so that it can be screwed into a coolant passage in an engine's intake manifold, cylinder head, or block. The level of thermal resistance in the ECT sensor decreases as the coolant heats up and flows through it. This results in an increase in voltage in the ECT sensor circuit at the PCM. As the engine cools, the resistance of the sensor increases and as a result, the voltage of the ECT sensor circuit (on the PCM) decreases. The PCM recognizes these voltage fluctuations as changes in engine coolant temperature. Fuel delivery and spark advance strategy are functions that are affected by the actual engine coolant temperature and input from the ECT sensor.

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

If the PCM detects voltage signals from the ECT sensor and the coolant temperature sensor that differ from each other by more than the maximum allowable parameter, a P00B6 code will be stored and a malfunction indicator lamp (MIL) may illuminate. It may take multiple driving cycles with failure to illuminate the MIL.

Example of a radiator coolant temperature sensor:

What is the severity of this DTC?

Since the ECT sensor input is critical to fuel delivery and ignition timing, conditions that contribute to the persistence of the P00B6 code must be addressed urgently.

What are some of the symptoms of the code?

Symptoms of a P00B6 engine code may include:

• Excessively rich exhaust
• Handling issues
• Poor idle quality
• Severely reduced fuel efficiency

What are some of the common causes for the code?

Reasons for this engine code may include:

• Defective ECT sensor
• Defective radiator coolant temperature sensor
• Insufficient coolant level
• Short circuit or open circuit or connectors
• Bad PCM or PCM programming error

What are some steps to troubleshoot the P00B6?

Before attempting to diagnose any stored codes associated with an ECT sensor, make sure the engine is full of coolant and not overheating. Before proceeding, the engine must be filled with the correct coolant and under no circumstances should it overheat.

Diagnosing a P00B6 code will require a valid vehicle information source, a diagnostic scanner, a digital volt / ohmmeter (DVOM), and an infrared thermometer with a laser pointer.

The next step, if the engine is not overheating, should be a visual inspection of the wiring and connectors of the coolant temperature sensor and the radiator coolant temperature sensor.

Prepare to retrieve all stored codes and freeze frame data by connecting the scanner to the vehicle's diagnostic port. As soon as you get this information, write it down as it may be useful as you continue to diagnose. Then clear the codes and test drive the vehicle to make sure the code is cleared.

Your vehicle information source will provide you with wiring diagrams, connector pinouts, component test specifications, and connector types. These things will help you test individual circuits and sensors with DVOM. Check individual system circuits with DVOM only after disconnecting the PCM (and all associated controllers). This will help protect against damage to the controller. Connector pinout diagrams and wiring diagrams are especially useful for checking the voltage, resistance, and / or continuity of individual circuits.

How to check the radiator coolant temperature sensor and the coolant temperature sensor:

• Find the correct component testing procedures / specifications and wiring diagram in your vehicle information source.
• Disconnect the sensor under test.
• Place DVOM on the Ohm setting
• Use DVOM test leads and component test specifications to test each sensor.
• Any sensor that does not meet manufacturer's specifications should be considered defective.

How to measure the reference voltage and ground at the radiator coolant temperature sensor and the coolant temperature sensor:

• Key on and engine off (KOEO), connect the positive test lead of the DVOM to the reference voltage pin of each sensor connector (test one sensor at a time)
• Use negative test lead to test the ground pin of the same connector (at the same time)
• Check reference voltage (typically 5V) and ground at individual sensor connectors.

How to check radiator coolant temperature sensor and ECT sensor signal voltage:

• Reconnect the sensors
• Test the signal circuit of each sensor with the positive test lead from the DVOM.
• The negative test lead must be connected to the ground pin of the same connector or to a known good motor / battery ground.
• Use an infrared thermometer to check the actual coolant temperature on each sensor.
• You can use the temperature and voltage chart (found in the vehicle information source) or the data display on the scanner to determine if each sensor is working properly.
• Compare the actual voltage / temperature with the desired voltage / temperature
• Each sensor should reflect the actual temperature or voltage of the coolant. If any of these do not work, suspect that it is faulty.

Check the individual signal circuits at the PCM connector if the individual sensor signal circuits reflect the correct voltage level at the sensor connector. This can be done using DVOM. If the sensor signal found at the sensor connector is not present on the corresponding PCM connector circuit, there is an open circuit between the sensor in question and the PCM. 

Only after exhausting all other possibilities and if all radiator coolant temperature and ECT temperature sensors and circuits are within specifications, can you suspect a PCM failure or PCM programming error.

• Finding technical service bulletins (TSBs) that are applicable to vehicle make and model, symptoms and stored codes can help you diagnose.

Related DTC discussions

• 2011 Chevy Aveo P00B6P00B6 Radiator Coolant Temperature / Engine Coolant Temperature Correlation. Can anyone tell me what this code means and why I can't find it? ... 

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