Technical Description of OBD-II Trouble Code
Low/Performance Engine Coolant Flow
What does that signify?
This generic powertrain diagnostic trouble code (DTC) is commonly found in many OBD-II vehicles, including Chevy, Audi, Ford, VW, and others. However, it appears to be more frequently detected in Chevrolet / Chevy vehicles such as Sonic, Aveo, Malibu, Spark, etc.
Whenever I have encountered a code P00B7, it indicates that the powertrain control module (PCM) has identified a discrepancy in the signals between the radiator coolant temperature sensor and the engine coolant temperature (ECT) sensor. This discrepancy may lead the PCM to conclude that the flow of engine coolant is restricted.
To ensure that coolant is flowing properly between the radiator and the engine cooling passages, the temperature of the coolant in the radiator is sometimes compared to the temperature of the coolant in the engine.
Here is an example of an engine coolant temperature sensor:
The design of the ECT sensor typically involves a thermal resistor that is dipped in a hard resin and sealed in a metal or plastic housing. Brass is commonly used for these housing materials due to its durability. In most cases, the ECT sensor is threaded so that it can be screwed into a coolant passage in the engine intake manifold, cylinder head, or block. The thermal resistance in the ECT sensor decreases as the coolant warms and flows across it, resulting in an increased ECT sensor circuit voltage at the PCM. As the engine cools, the sensor resistance increases and the ECT sensor circuit voltage to the PCM decreases. The PCM interprets these voltage fluctuations as changes in engine coolant temperature. Actual engine coolant temperature and input data from the ECT sensor affect functions such as fuel delivery and ignition timing strategy.
The radiator coolant temperature sensor monitors coolant temperature in a similar manner to the ECT sensor. It is usually inserted into one of the radiator tanks but can also be fitted into 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 by more than the maximum allowable parameter, a code P00B7 will be stored and a malfunction indicator lamp (MIL) may illuminate. Multiple drive cycles with a failure may be required for MIL illumination.
What is the severity of this DTC?
Since ECT sensor input is crucial for fuel delivery and ignition timing strategy, it is important to address the conditions contributing to a stored code P00B7 with urgency.
What are some of the symptoms of the code?
Symptoms of a P00B7 engine code may include:
What are some of the common causes of the code?
Possible causes for this engine code may include:
What are some P00B7 troubleshooting steps?
Before attempting to diagnose any stored ECT sensor related codes, it is important to ensure that the engine is full of coolant and not overheating. The engine must be filled with the proper coolant and should not overheat under any circumstances. It is also recommended to cold crank the engine and allow the thermostat to open while observing the temperature gauge or scanner data display.
To diagnose a code P00B7, you will need a reliable source of vehicle information, a diagnostic scanner, a digital volt/ohmmeter (DVOM), and an infrared thermometer with a laser pointer. Start by visually inspecting the wiring and connectors of the ECT sensor and radiator coolant temperature sensor system if the engine is not overheating.
Connect the scanner to the vehicle diagnostic port to retrieve all stored codes and freeze frame data. Write down this information as it may be helpful during the diagnosis. Clear the codes and test-drive the vehicle to see if the code is reset.
Your vehicle information source will provide you with wiring diagrams, connector pin-out charts, component testing specifications, and connector views. These resources will assist you in testing individual circuits and sensors using the DVOM. Test individual system circuits using the DVOM only after disconnecting the PCM and all related controllers to prevent controller damage. Connector pin-out charts and wiring diagrams are particularly useful for testing individual circuit voltage, resistance, and continuity.
Here is how to test the radiator coolant temperature sensor and the ECT sensor:
Here is how to probe for reference voltage and a ground at the radiator coolant temperature sensor and ECT sensor:
Here is how to test the radiator coolant temperature sensor and ECT sensor signal voltage:
If the individual sensor signal circuits reflect the correct degree of voltage at the sensor connector, test the individual signal circuits at the PCM connector using the DVOM. This will help identify any open circuit between the sensor in question and the PCM.
If all other possibilities have been exhausted and all radiator coolant temperature and ECT temperature sensors and circuits are within specifications, you may consider the possibility of PCM failure or a PCM programming error.
