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 Descriptors

DTC P00B7: Radiator Coolant Temperature (RCT) Insufficient Flow

### Circuit Description

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

### Conditions for Running the DTC

• | DTCs P00B3, P00B4, P00B6, P0116, P0117, and P0118 are not set.

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

| OR

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

• | The DTC runs continuously 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 45°C (113°F) when the ECT sensor is warmer than 117°C (242°F).

### Action Taken When the DTC Sets

DTC P00B7 is a Type B DTC.

### Conditions for Clearing the MIL/DTC

DTC P00B7 is a Type B DTC.

### Diagnostic Aids

• | The thermostat 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 Cooling Schematics

#### 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, P00B4, P00B6, P0117, P0118, P0480, P0481, P0597, P0598, and P0599 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 cooing fan operates. Refer to Cooling Fan Inoperative.
4. Engine idling for 15 minutes with the A/C OFF.

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

5. Command the Engine Coolant Thermostat Heater to 100 percent with a scan tool. Increase the engine speed to 3,000 RPM. Observe the scan tool ECT sensor parameter. 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

- | Radiator hoses

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

⇒ | If you find any of the above conditions, repair as necessary.

2. If all conditions test normal, replace the engine coolant thermostat heater.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Engine Coolant Thermostat Replacement