For 1990-2009 cars

### Circuit Description

This code will set if the output of the heater core coolant sensor indicates a probable short circuit or an open in the sensor or the associated wiring harness, or a malfunction of the automatic temperature controller (ATC).

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 |

1. Disconnect the heater core coolant temperature sensor connector from the automatic temperature controller (ATC) harness.
2. Examine the wiring from the sensor to the connector and examine the connector for any signs of damage.
3. Measure the resistance between the heater core coolant temperature sensor connector terminals.

Is there any sign of damaged wiring or connector, or is the resistance outside the specified value at 20-25°C (68-77°F)?

2,100-2,600 ohms

Go to Step 2

Go to Step 3

2 | Repair the damaged wiring or the connector, or replace the heater core coolant temperature sensor as required. Is the repair complete? | -- | System OK | --
3 |

1. Turn ON the ignition, with the engine OFF.
2. Measure the voltage between the 2 heater core coolant temperature sensor connector terminals on the ATC harness.

Does the voltage measure less than the specified value?

4 V

Go to Step 7

Go to Step 4

4 | Inspect the terminals on the heater core coolant temperature sensor connector. Is any problem found with the connector? | -- | Go to Step 5 | Go to Step 6
5 | Repair the connector terminals or replace the heater core coolant temperature sensor or ATC as required. Is the repair complete? | -- | System OK | --
6 |

1. Reconnect the heater core coolant temperature sensor to the ATC harness.
2. Turn ON the ignition, with the engine OFF.
3. Observe the temperature display area.

Does this display indicate the continuing presence of a code 3 condition?

--

Go to Step 9

System OK

7 |

1. Pull the ATC from the instrument panel, leaving the wiring harness connected.
2. Measure the voltage between terminals A13 and B9 by backprobing the connectors.

Does the voltage measure less than the specified value?

4 V

Go to Step 9

Go to Step 8

8 |

1. Trace the wiring from controller terminals A13 and B9 to the coolant temperature sensor connector terminals on the ATC harness connectors.
2. Repair any open or high resistance found in the wiring or connector terminals.

Is the repair complete?

--

System OK

--

9 | Replace the ATC. Refer to Heater and Air Conditioning Control Replacement . Is the repair complete? | -- | System OK | --