Technical Description of OBD-II Trouble Code
The circuit for the Radiator Coolant Temperature Sensor is registering a high reading.
What does that mean?
This diagnostic trouble code (DTC) is applicable to all OBD-II vehicles, including Mercedes, Vauxhall, Nissan, BMW, Mini, Chevy, Mazda, Honda, Acura, Ford, etc.
The cooling system is an essential part of your vehicle’s engine system. It not only monitors the engine’s temperature but also regulates it. This is achieved through various electrical and mechanical components such as the Coolant Temperature Sensor (CTS), radiator, water pump, thermostat, etc.
The Engine Control Module (ECM) uses the values from the CTS to accurately monitor and regulate the engine’s temperature. Different temperatures require different air/fuel mixtures, so it is crucial for the CTS to function within the desired ranges. Most CTS sensors are Negative Temperature Coefficient sensors, meaning their resistance decreases as the temperature rises. Understanding this is helpful for troubleshooting.
The ECM triggers the P00B1 code and associated codes when it detects a condition outside the specific electrical range of the CTS or its circuit. The ECM may detect an intermittent issue (P00B5) that comes and goes. In my experience, the culprit is often mechanical, but electrical faults can also be the cause.
The P00B4 code is set when the ECM detects a high specific electrical value within the radiator CTS or its circuit. It is one of five related codes: P00B1, P00B2, P00B3, P00B4, and P00B5.
What is the severity of this DTC?
This code is considered moderately severe. The severity will depend on the symptoms and how the fault is affecting your vehicle’s performance. Since the functionality of the CTS directly influences the engine’s air/fuel mixture, it is important not to ignore this issue. Neglecting it could lead to expensive engine repairs.
Here is an example of a radiator coolant temperature sensor:
What are some of the symptoms of the code?
Symptoms of a P00B4 diagnostic code may include:
What are some of the common causes of the code?
Possible causes for this code include:
What are some P00B4 troubleshooting steps?
Check for any technical service bulletins (TSBs) related to your vehicle. Having access to a known fix can save time and money during diagnosis.
Tools
Here are some tools you may need when diagnosing or repairing the radiator coolant temperature sensor circuits and systems:
Safety Tips
NOTE: ALWAYS verify and record the integrity of your battery and charging system before further troubleshooting.
Basic Step #1
If this code is set, the first thing to do is inspect the radiator coolant temperature sensor for any obvious signs of damage. These sensors are typically mounted in the radiator or along the coolant lines/hoses, but they can also be found on the cylinder head or other locations. Refer to your service manual for the exact location.
NOTE: When diagnosing or repairing anything related to the cooling system, make sure the engine is completely cooled down before proceeding.
Basic Step #2
Test the sensor. Since the internal resistance of the sensor changes with temperature, you will need to determine the desired resistance/temperature (refer to the manual). Using a multimeter, test the resistance between the pins of the radiator CTS. Any reading outside the desired range indicates a defective sensor that should be replaced.
NOTE: Over time and exposure to the elements, the plastic of these sensors can become brittle. Be careful not to damage the connectors during diagnosis or repair.
Basic Tip #3
Check for leaks. Ensure that the sensor is not leaking around its seal. A leak here can cause erratic readings as air enters the system. Replacing the gaskets/seals is usually inexpensive and easy. Regardless of whether it is the root cause of your problem or not, it should be addressed before proceeding.
NOTE: Refer to your service manual to determine the specific antifreeze/coolant to be used. Using the wrong type can cause internal corrosion, so make sure to use the correct product.
Basic Step #4
Pay special attention to the routing of the CTS harness, considering its location. These sensors and their corresponding harnesses are exposed to extreme heat and the elements. Damaged wiring is a common issue, so repair any wiring that is broken or melted.
Basic Step #5
Clean the CTS. If possible, remove the sensor from the vehicle to inspect for any debris or residue that could affect its ability to provide accurate readings.
