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 P00B6 00: Radiator Coolant Temperature (RCT) - Engine Coolant Temperature (ECT) Not Plausible

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
RCT sensor signal | P00B3 00 | P00B4 00 | P00B4 00* | P00B6 00
Low reference | -- | P00B4 00 | P00B4 00* | P00B6 00
*Engine control module (ECM) or sensor damage may occur if the circuit is shorted to B+

### Typical Scan Tool Data

#### ECT Sensor 2

Circuit | Short to Ground | Open | Short to Voltage
--- | --- | --- | ---
Operating Conditions: The ignition is ON, or the engine is running Parameter Normal Range: Varies with ambient temperature, within a range of -39 to +120°C (-38 to +248°F)
RCT sensor signal | 150°C (302°F) | -40°C (-40°F) | -40°C (-40°F)
Low reference | -- | -40°C (-40°F) | -40°C -40°F)

### Circuit/System Description

The radiator coolant temperature (RCT) sensor is a variable resistor that measures the temperature of the radiator coolant. The ECM supplies 5 V to the RCT sensor signal circuit and supplies a ground for the low reference circuit.

The following table illustrates the difference between temperature, resistance, and voltage:

RCT | RCT Resistance | RCT Signal Voltage
--- | --- | ---
Cold | High | High
Warm | Low | Low

### Conditions for Running the DTC

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

• | The ignition has been off for greater than 8 hours before vehicle is started.

• | The ignition is ON, or the engine is running.

• | The intake air temperature (IAT) is greater than -7°C (19°F).

• | The fuel level is greater than 10 percent.

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

### Conditions for Setting the DTC

This DTC sets if one of the following conditions occurs for less than 1 s:

• | The ECM detects the RCT sensor and the ECT sensor are greater than a predetermined intake air temperature at engine start-up.

• | The ECM detects the RCT sensor is 20°C (68°F) warmer than the ECT sensor at engine start-up and the block heater has not been detected.

• | The ECM detects the RCT sensor is 20°C (68°F) warmer than the ECT sensor at engine start-up and the engine has been cranking for greater than 10 s without a fuel level sensor DTC.

### Action Taken When the DTC Sets

DTC P00B6 00 is a Type B DTC

### Conditions for Clearing the DTC

DTC P00B6 00 is a Type B DTC

### Diagnostic Aids

• | If the vehicle has sat overnight, the RCT sensor and the ECT sensor values should display within 3°C (5°F).

• | As the thermostat opens, the RCT sensor temperature should rise steadily, then stabilize once the thermostat opens completely.

• | Test the RCT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor.

• | Inspect for the correct operation of the engine cooling system and verify the correct coolant level.

• | If the condition is intermittent, allowing the vehicle to sit for greater than 8 hours with the ignition OFF, may help isolate the condition. Compare the scan tool RCT and ECT temperature sensor values at Ignition ON. The RCT sensor and the ECT sensor values should display within 3°C (5°F).

### 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, 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. Engine idling for 15 min with the A/C OFF.

Note: Depending on ambient temperature, it may take up to 4 min for the temperatures to equalize.

4. Command the engine coolant thermostat heater to 100% with a scan tool. Increase the engine speed to 3000 RPM. Observe the scan tool RCT and the ECT sensor parameters. The RCT and the ECT sensor parameters should be within 20°C (68°F).
5. 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, disconnect the harness connector at the B34B Radiator Coolant Temperature (RCT) Sensor.
2. Ignition OFF, test for less than 5 Ω between the low reference circuit terminal 2 and ground.

⇒ | If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the K20 engine control module.

3. Ignition ON, verify the scan tool B34B Radiator Coolant Temperature (RCT) Sensor parameter is -40°C (-40°F).

⇒ | If greater than the specified range, test the signal circuit terminal 1 for a short to ground. If the circuit tests normal, replace K20 Engine Control Module.

Note: If the fuse in the jumper wire opens, the signal circuit is shorted to a voltage and the sensor may be damaged.

4. Install a 1 A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 2. Verify the scan tool B34B Radiator Coolant Temperature (RCT) Sensor parameter is at 150°C (302°F).

⇒ | If less than specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.

5. If all circuits test normal, test or replace the B34B Radiator Coolant Temperature (RCT) Sensor.

### Component Testing

#### Static Test

1. Ignition OFF, disconnect the harness connector at the B34B Radiator Coolant Temperature (RCT) Sensor.

Note: A thermometer can be used to the used to test the sensor off the vehicle.

2. Test the B34B Radiator Coolant Temperature (RCT) Sensor by varying the sensor temperature while monitoring the sensor resistance. Compare the readings with the table and verify that the resistance Temperature Versus Resistance table and verify that the resistance is within 5 percent of the specification.

⇒ | If not within the specified range, replace the B34B radiator coolant temperature (RCT) sensor.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | LINK (Radiator Coolant Temperature (RCT) Sensor Replacement).

• | Control Module References for ECM replacement, setup, and programming