P00B7 – Engine Coolant Flow Low/Performance (Chevrolet)

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By Reinier (Contact Me)
Last Updated 2024-03-31
Automobile Repair Shop Owner
CodeFault LocationProbable Cause
P00B7 Engine Coolant Flow Low/Performance
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Table of Contents

  1. What Does Code P00B7 Mean?
  2. Where is the P00B7 sensor located?
  3. What are the common causes of code P00B7?
  4. How expensive is it to fix code P00B7?
  5. What are the symptoms of code P00B7?
  6. What are common solutions to code P00B7?
  7. How serious is code P00B7?
  8. How do you troubleshoot code P00B7?
  9. Get Help with P00B7

What Does Code P00B7 Mean?

OBD II fault code is a generic trouble code that is defined by carmaker Chevrolet as P00B7 – “Engine Coolant Flow Low/Performance”, or sometimes as P00B7 – “Radiator Coolant Temperature (RCT) Insufficient Flow”, and is set when the PCM (Powertrain Control Module) detects an insufficient flow of coolant through one or more cooling radiators.

Note that in the context of code P00B7, the PCM compares the signal voltages from two or more coolant temperature sensors within a cooling system to determine the rate of coolant flow through one or more of the four separate cooling systems on Chevy Volt hybrid vehicles.

Background/tech notes

Although all hybrid vehicles have multiple cooling systems, none is as complicated as the four cooling systems that serve various components on Chevy Volt models. In addition to the three separate liquid cooling systems that serve the internal combustion engine, HV battery pack, and power electronics, there is also a separate cooling loop that uses gaseous refrigerant to help cool the coolant that regulates the temperature of the HV battery pack.

As a practical matter, the cooling systems on Chevy Volt vehicles are far too complex to provide a comprehensive description of each system here. However, we can do the next best thing, which is to describe the function of some of the most critical components that can cause not only one or more cooling systems to stop working as expected when they fail but can also cause potentially fatal damage to the systems they control or regulate. Let us start with the-

Three-way coolant flow control valve

This valve is controlled by the Hybrid Powertrain Control Module 2, and its function is to direct coolant to the radiator, the heat exchanger, or the bypass circuit, depending on the temperature of the HV battery pack. Several coolant temperature sensors and battery temperature probes monitor both the ambient temperature and the temperature of the HV battery, and if battery heating is required in low temperatures is required, Hybrid Powertrain Control Module 2 will activate a dedicated electrically operated coolant pump and move the three-way valve to position “A”. This allows coolant to flow through dedicated channels in the battery housing to raise the battery’s temperature.

If battery cooling is required, the control module will set the three-way valve to position “B” to allow coolant to pass through the dedicated refrigerant heat exchanger, which cools the coolant to a point where it can effectively absorb heat from the HV battery.

When the HV battery’s temperature is stable, the control module will set the three-way valve to position “C”, which allows coolant to flow freely between the HV battery’s casing and the radiator. If the coolant flow is unrestricted the circulation of the coolant will maintain the HV battery’s temperature stable and within an acceptable range.

NOTE: While the three-way valve is not a common failure point, there are several reasons why it could stop working as expected, with damaged wiring and open circuits being the most common reasons for the valve not working.

Debris filter

The HV battery’s cooling circuit incorporates a debris filter. The function of this filter is to protect the dedicated coolant pump that “drives” the HV battery’s coolant circuit against damage caused by scale, rust, and other solid particulate matter in the coolant that develops in this cooling system over time.

NOTE: Clogging and plugging of this filter is extremely common on vehicles that are poorly maintained. To prevent this from occurring, the coolant in the engine and other cooling systems must be replaced strictly per the manufacturer’s recommendations. It’s worth noting that if the debris filter is clogged or restricted, the part of the radiator that supports the HV battery’s cooling system will show an almost immediate (and steep) rise in temperature after the vehicle has been operating for a few minutes. See the “Location” section below for details on which part of the radiator serves the HV battery’s cooling system. If this section of the radiator heats up very quickly, it is almost certain that the debris filter is blocked or restricted.

Radiator cooling fans

NOTE: It is unlikely that the failure of one or both radiator cooling fans will cause just one part of the radiator to heat up significantly more than any other part, as would happen when the debris filter or three-way valve fails.

In practice, the failure of one or both radiator cooling fans will set one or more trouble codes that relate directly to the operation of the cooling fans. Bear in mind, though, that radiator cooling fan failures could cause the uneven heating of a shared radiator.

Where is the P00B7 sensor located?

This diagram shows the layout and arrangement of the conglomerate of radiators that regulate the temperatures of not only the internal combustion engine in Chevy volt hybrids but also the temperature of the transmission and power electronics.

It is important to note that while the HV battery cooling/heating and power electronics cooling systems appear to share a common radiator, this radiator is in fact two separate radiators that each has its own expansion tank/coolant reservoir, as shown in the image below-

What are the common causes of code P00B7?

NOTE #1: The most common causes of code P00B7 on Chevy Volt vehicles are many and varied, but it should be noted that since the definition(s) of code P00B7 (Engine Coolant Flow Low/Performance / Radiator Coolant Temperature (RCT) Insufficient Flow) does not indicate which of the four cooling systems is/are affected, determining the exact root cause(s) of code P00B7 on Chevy Volt vehicles can sometimes be challenging even for professional mechanics.

NOTE#2: Only three of the four cooling systems on Chevy Volt vehicles use conventional coolant. The fourth cooling system, which keeps the transaxle cool, uses the transmission fluid as coolant.

Nonetheless, some common causes of code P00B7 on Chevy Volt vehicles could include one or more of the following-

  • Low coolant levels
  • The use of incorrect, unsuitable, or degraded coolant
  • Damaged, burnt, shorted, corroded, or disconnected wiring or connectors almost anywhere in any cooling system
  • Faulty or malfunctioning HV battery pack coolant pump
  • One or more defective or malfunctioning coolant temperature sensors
  • Blocked or restricted debris filter in the HV battery pack’s cooling system (Common on poorly maintained vehicles)
  • Defective, malfunctioning, or stuck three-way coolant flow control valve that routes coolant through the radiator, the heat exchanger, or the bypass circuit
  • Defective or malfunctioning thermostat
  • Failed or failing Hybrid Powertrain Control Module 2, but note that since is a rare event, the fault must be sought elsewhere before any control module is replaced or reprogrammed

TIP: One way to narrow down the search for possible causes of this code is to use an infrared-based thermometer to take readings of the temperature differences between the radiators serving the HV battery pack and the power electronics. As a general rule of thumb, these readings should be within about 10-15 degrees of each other after the vehicle has been driven for about 30 minutes, although there are exceptions to this rule. Nonetheless, if a large temperature difference exists, the system that is the hottest will usually be the system with the fault or defect. See the section on “location” for details on how the various cooling radiators are arranged.

How expensive is it to fix code P00B7?

Due to the high number of possible causes of code P00B7 on Chevy Volt vehicles, it is not possible to provide accurate estimates of repair costs here, since repair costs are entirely dependent on a) the nature of the problem, and b) the system that is affected.

Also, bear in mind that because of the complexity of the cooling systems on Chevy Volt vehicles, diagnosing the problem could take several hours, which will significantly increase the final repair bill.

Based on the above, the best course of action to follow would be to consult several repair shops with proven experience in diagnosing cooling system issues on Chevy Volt vehicles to obtain repair estimates that include all costs, as well as all fees, taxes, and levies that may be payable in your location. Failing to do this could leave you with a repair bill that may be far higher than you are willing or prepared to pay.

What are the symptoms of code P00B7?

The symptoms of code P0078 on Chevy Volt vehicles depend on which cooling system is affected, but some common symptoms could include one or more of the following-

  • Stored trouble code and an illuminated warning light
  • Depending on both the nature of the problem and the affected cooling system, multiple additional trouble codes may be present along with P00B7, with the most common additional codes relating to the HV battery pack’s temperature, or its state of charge
  • Abnormal temperature readings on the temperature gauge on the dashboard
  • The vehicle may not “power on”
  • Failure of the HV battery pack could occur if its temperature cannot be regulated effectively
  • Failure of the power electronics could occur if its temperature cannot be regulated effectively

What are common solutions to code P00B7?

Some possible solutions could include one or more of the following-

  • Inspect all coolant hoses and replace damaged or suspect hoses as required
  • Locate and repair coolant leaks as required
  • Replace the debris filter in the HV battery pack’s cooling system, but be aware that significant coolant losses may occur during the filter replacement
  • Replace coolant with fresh coolant of the correct grade and formulation (50/50 Dexcool or other GM6277M compliant coolant, but be aware that air will enter the cooling systems; all trapped air must be purged strictly according to OEM service procedures. Failing to follow such instructions could cause one or more cooling systems to stop working, which if it happens, could cause serious and even fatal damage to major components or systems

WARNING: To prevent damage to the vehicle’s cooling systems, we do NOT recommend that non-professional mechanics attempt any diagnostic or repair procedures other than the few options listed here because of the very complex nature of the overall cooling systems on Chevy Volt vehicles.

 

How serious is code P00B7?

All instances of code P00B7 should be considered serious and should be investigated and resolved without undue delay. Ideally, the vehicle should not be driven or operated while code P00B7 remains unresolved because of the high likelihood that serious and even fatal damage could occur to major components, including the internal combustion engine, HV battery pack, the power electronics, and the transaxle.

How do you troubleshoot code P00B7?

Because of the complex nature of the overall cooling system of Chevy Volt vehicles, we do NOT recommend that non-professional mechanics attempt ANY diagnostic or repair procedure on ANY part of ANY cooling system on the vehicle.

The possibility of causing even inadvertent damage to cooling system components is extremely high, but the biggest danger lies in the possibility that ill-considered or incorrect testing of some components could cause serious personal injuries or even instant death through electrocution by the high-voltage system.

Based on the above, we strongly recommend that you seek professional assistance with diagnosing and resolving any issues with the cooling systems on Chevy Volt vehicles.

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