Fix P00B7: Mechanic’s solutions that WORKED

The code P00B7: Engine Coolant Flow Performance points out a fault related to engine coolant flow performance. While not extremely serious, it can lead to reduced engine power and should be addressed to prevent potential issues. This fault code is typically associated with radiator issues, air pockets in the cooling system, problems with the PCM-controlled radiator fan, faulty thermostats, or other cooling system component failures.

P00B7 quick overview

Description	P00B7: Engine Coolant Flow Performance
Is it serious?	This code is typically not extremely serious, but it can lead to reduced engine power and should be addressed to prevent potential issues.
Possible causes	– Radiator issues, including cracks or coolant flow problems – Air pockets in the cooling system – PCM-controlled radiator fan not functioning correctly – Faulty thermostat or thermostat operation – Cooling system component failures
How to diagnose?	Inspect the radiator for cracks or flow problems. Properly bleed the cooling system to eliminate air pockets. Verify the operation of the PCM-controlled radiator fan. Check the thermostat and its operation. Inspect other cooling system components for failures. Consider performing a block test to check for combustion gas in the cooling system.

How to fix P00B7 – learn from mechanics

I looked into P00B7 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Ford

Vehicle Information: 2008 Ford F-350 Super Duty Lariat 6.4L

Issue + Repair History: The customer requested a DPF/CAT delete with an Edge racing program. However, the instrument cluster/message center displayed a low-power mode warning that would reset when the truck was turned off but reappear after 30-40 minutes. The only diagnostic trouble code (DTC) found was P00B7. The customer also mentioned that the truck had been stolen, and a door module was installed.

Other OBD2 Codes + Test Results: P00B7 – Coolant system performance (no detailed description available)

Suggestions to Fix Issue:

1. Requested PIDs (Parameter IDs) for further diagnosis.
2. Considered the possibility of a PCM reflash, as some of these trucks were recalled for it.
3. Checked coolant level and condition, as well as the radiator cap.
4. Monitored engine coolant temperature (ECT) to determine thermostat performance.
5. Replaced thermostats if ECT exceeded 170.6°F.
6. Suggested additional testing if necessary.

Final Fix: The issue was resolved by following the procedure outlined by Arren Connors. The thermostats were replaced, resulting in improved fuel economy from 20L/100kms to 16L/100kms. The specific details of the code P00B7 were not available, but the thermostat replacement addressed the performance issue.

Case #2: Ford

Vehicle Information: 2008 Ford F-450 Super Duty XL 6.4L

Issue + Repair History: The truck initially came in with low power and the SES (Service Engine Soon) light on due to the EGR temperature sensor (EGRt sensor) issue. The EGR was cleaned, and the EGRt temp sensor2 on the right-hand exhaust pipe was replaced. All TSBs (Technical Service Bulletins) and reflashes were performed at the dealer, resolving the problem temporarily. However, it returned with a reduced power light and the following trouble codes: P0529 and P00B7.

Other OBD2 Codes + Test Results: P0529 – Cooling fan circuit intermittent P00B7 – Cooling system low flow

Suggestions to Fix Issue:

1. Check for exhaust leaks in the manifolds and ensure that the turbochargers are operational, as exhaust leaks and inoperative turbos can raise EGRt temperature readings, leading to reduced power.
2. Provide test results and diagnostic information for more accurate responses.
3. Examine the harness at the firewall where it connects to the motor for broken wires, as there is a TSB related to broken wires causing low-pressure codes, EGR codes, and boost pressure codes.
4. Inspect the boost pressure sensor for blockage; if it resembles a MAP sensor, suspect harness damage.
5. Check the thermostat for possible issues, as a broken thermostat spring can trigger the P00B7 code.

Final Fix: The issue was resolved by replacing the thermostat, as the spring was found to be broken. Additionally, the clutch fan was replaced due to an internal short that would act up only when wet. These actions addressed the reduced power and trouble codes P0529 and P00B7.

Case #3: Chevrolet

Vehicle Information: 2014 Chevrolet Sonic LS 1.8L

Issue + Repair History: The customer complained of overheating and the MIL (Malfunction Indicator Lamp) illuminated with fault codes P00B7 (coolant flow insufficient) and P0118 (ECT circuit high). The vehicle lacks a temperature gauge, relying on a warning light. During testing, there was a significant difference between the radiator temperature sensor and ECT (Engine Coolant Temperature) sensor readings. ECT reached 240°F, while the radiator temp sensor only reached about 130°F. Although the ECT is in a plastic housing, readings at the rear of the head and coolant hose with a thermal imager matched actual ECT readings. The radiator remained cool, and the fans were operational. No hot air was produced. The water pump was inspected, expecting a possible impeller problem, but no obvious issue was found. The thermostat had been replaced in October 2018, according to the customer.

Other OBD2 Codes + Test Results: None mentioned.

Suggestions to Fix Issue:

1. Check the radiator temp sensor, as it may be a two-wire sensor, and the diagnostic tree is straightforward.
2. Verify if there’s no hot air in the HVAC vents.
3. Ensure power and ground to the thermostat, as a 100% command with a cold radiator indicates the PCM (Powertrain Control Module) is attempting to open the thermostat but it may not be functioning correctly.
4. Investigate the ECT sensor wiring for an intermittent open circuit or issues with the sensor itself. Confirm if the ECT and radiator sensors agree after a cold soak.
5. Remove the thermostat (if possible) to check for flow; if flow is restored, it suggests a failing thermostat. Aftermarket thermostats are known for this issue.

Final Fix: The issue was resolved by replacing the thermostat, which was found to be faulty. Testing revealed that the thermostat was not opening from heat as it should, leading to the temperature discrepancies and overheating. After replacing the thermostat, the vehicle operated correctly, and the temperature readings were consistent between the radiator and ECT sensors.

Case #4: Ford

Vehicle Information: 2008 Ford F-350 Super Duty XL 6.4L

Issue + Repair History: The truck experienced an issue where the check engine light and wrench light would come on, and the PCM would reduce engine power. The codes retrieved were P00B7 for engine coolant flow performance. This code appeared after a PCM reprogramming recall had been performed at the dealer. The technician followed pinpoint test K, which stated that the engine coolant temperature (ECT) should be at 170 degrees F or less at steady idle. However, the ECT was consistently around 197 degrees F. The thermostat was replaced, the cooling system was refilled using a vacuum fill adapter, and a test drive was conducted. The problem persisted, and the lower radiator hose remained cool, with the right side of the radiator staying cold to the touch. Subsequently, the water pump, radiator, and radiator cap were replaced, and the vacuum system was used to fill the cooling system. After these repairs, the truck did not experience reduced power again. However, the ECT still showed a temperature above 170 at steady idle.

Other OBD2 Codes + Test Results: None mentioned.

Suggestions to Fix Issue:

1. Investigate the possibility of a radiator issue, as a cracked radiator could cause improper cooling system efficiency.
2. Ensure that the cooling system is bled properly to eliminate air pockets.
3. Check the PCM-controlled radiator fan for proper operation. Perform a manual test with scan tools to verify its functionality.
4. Examine the PCM connectors and pins for tightness and a good connection, as intermittent codes following a PCM reprogramming recall may be related to loose connections.
5. Consider the possibility of other vehicles experiencing similar issues and compare the findings.

Final Fix: The issue was resolved after replacing the radiator. It was noted that the cooling system did not leak much, only about half a gallon or less, and once the coolant level dropped below the crack in the radiator, it stopped leaking. However, the cooling system did not pressurize as expected. Fixing the radiator addressed the problem, and the truck no longer experienced reduced power. The technician also observed that the sensitivity of the PCM had increased with the new flash, which led to more precise temperature monitoring. The ECT of the truck fluctuated less and stayed within a smaller temperature range after the radiator replacement. The customer did not report any further issues with the vehicle.

Advice	Brief Description of Diagnostic Step
Check for radiator issues	Investigate the radiator for cracks or other cooling system problems.
Properly bleed the cooling system	Ensure the cooling system is thoroughly bled to eliminate air pockets.
Verify PCM-controlled radiator fan operation	Use scan tools to manually test and confirm the operation of the PCM-controlled radiator fan.
Inspect PCM connectors and pins	Check PCM connectors and pins for tightness and a good connection, especially after PCM reprogramming.
Consider radiator replacement	If other measures fail, consider replacing the radiator to address the issue.