For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P00B7 00: Engine Coolant Flow Insufficient

### Circuit/System Description

The engine control module (ECM) monitors the temperature of the radiator coolant temperature (RCT) sensor. The engine coolant thermostat heater is controlled by the ECM. The ECM controls the engine coolant thermostat heater with a pulse width modulated (PWM) signal. The ECM compares the radiator coolant temperature (RCT) sensor to the engine coolant temperature (ECT) sensor in order to regulate coolant flow through the radiator.

### Conditions for Running the DTC

• | DTCs P00B3 00, P00B4 00, P0112 00, P0113 00, P0117 00, or P0118 00 are not set.

• | The engine run time is greater than 300 s.

| or

• | The engine coolant temperature (ECT) sensor is greater than 106°C (223°F).

• | The DTC runs once per ignition cycle when the above conditions are met.

### Conditions for Setting the DTC

The ECM detects the difference between the RCT sensor and the ECT sensor is greater than 30°C (68°F) when the ECT sensor is warmer than 117°C (242°F).

### Action Taken When the DTC Sets

DTC P00B7 00 is a Type B DTC

### Conditions for Clearing the DTC

DTC P00B7 00 is a Type B DTC

### Diagnostic Aids

• | The engine coolant thermostat heater has a mechanical fail-safe in case of an electrical condition with the thermostat heater. The mechanical thermostat will open at approximately 104°C (220°F). The mechanical thermostat will cycle from approximately 104°C (220°F) to approximately 98°C (208°F).

• | A resistance condition in the RCT sensor circuits may cause this DTC. This condition results in a greater voltage on the RCT sensor signal circuit, which is interpreted by the ECM as a colder RCT.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTC P00B3 00, P00B4 00, P0117 00, P0118 00, P0480 00, P0481 00, P0597 00, P0598 00, or P0599 00 should not be set.

⇒ | If a DTC is set, refer to Diagnostic Trouble Code (DTC) List - Vehicle for further diagnosis.

2. Verify the coolant in the radiator surge tank is at the correct level and there are no engine coolant leaks. Refer to Cooling System Draining and Filling and Loss of Coolant.
3. Verify the engine cooling fan operates. Refer to Cooling Fan Inoperative.

Note: Depending on ambient temperature, it may take up to 4 min for the temperature to decrease less than the specified value.

4. Engine idling for 15 min with the A/C OFF.
5. Command the Engine Coolant Thermostat Heater to 100% with a scan tool. Increase the engine speed to 3000 RPM. Observe the scan tool ECT sensor parameters. The temperature should decrease to less than 85°C (185°F).
6. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the freeze frame / failure records data.

### Circuit/System Testing

1. Ignition OFF, inspect the cooling system for the following conditions:

• | Weak coolant solution

• | Obstructed radiator air flow or bent radiator fins

• | Blocked cooling system passages

• | Radiator hoses that are restricted, collapsed, or deteriorated

• | Damaged water pump

• | Loss of cooling system pressure

• | Leaking surge tank cap

• | Leaking radiator hoses

• | Cylinder head or an engine block that is cracked or plugged

2. If you find any of the above conditions, repair as necessary.
3. If all conditions test normal, replace the E41 Engine Coolant Thermostat Heater.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Engine Coolant Thermostat Replacement.