For 1990-2009 cars

### Circuit Description

The PCM will richen the air/fuel ratio when a high coolant temperature is monitored. Called hot fuel enrichment (HFE) this condition can cause exhaust emissions to exceed the federal emissions standards for this vehicle. This DTC is required in order to prevent HFE from being active during a skewed ECT sensor condition or during an actual cooling system condition that results in hot engine coolant. The PCM will calculate an engine coolant temperature value based on IAT, engine speed, vehicle speed and engine load. If the ECT sensor value is higher than the calculated coolant temperature during the Conditions for Running the DTC, this DTC sets and HFE is disabled.

### Conditions for Running the DTC

• | DTCs P0101, P0102, P0103, P0107, P0108, P0117, P0118, P0125, P0502, or P1108 are not set.

• | Engine coolant temperature is the same or less than 110°C (230°F) at startup.

OR

• | The engine coolant temperature is less than 104°C (219°F) anytime at startup.

• | Intake Air Temperature, Engine Load, Engine Speed and Vehicle Speed are all within a specific range.

### Conditions for Setting the DTC

The PCM determines the monitored engine coolant temperature (from the ECT sensor) is more than the calculated coolant temperature.

### Action Taken When the DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

### Conditions for Clearing the MIL/DTC

• | The DTC becomes history when the conditions for setting the DTC are no longer present.

• | The history DTC clears after 40 malfunction free warm-up cycles.

• | The PCM receives a clear code command from the scan tool.

### Diagnostic Aids

• | The most likely cause of this DTC is a cooling system problem. Perform the Electric Cooling Fan Diagnosis and also visually inspect the cooling system for problems such as restricted radiator AIR flow. Refer to Engine Cooling for more cooling system diagnostic aids.

• | The IAT sensor must indicate the actual ambient temperature to within 1 degree. If the IAT sensor is accurate the ECT sensor must be inaccurate.

| Test of the ECT sensor can be made by comparing actual coolant temperature to the ECT scan tool display.

| Obtain actual coolant temperature using a thermometer located in the engine coolant. A test of the ECT sensors resistance may also be performed.

| If the actual coolant temperature is the same as the ECT scan tool display then the engine was not allowed to cool completely. Allow the vehicle to cool and repeat the diagnostic table.

### Test Description

The numbers below refer to the step numbers on the diagnostic table:

1. Compares temperature readings of the ECT and IAT sensors.

2. Tests the temperature of the ECT sensor.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 | Are any other DTCs set? | -- | Go to applicable DTCs | Go to Step 3
3 | Verify proper operation of the ECT and IAT sensor by performing the following:

Important: Sensors must be accurate to within 1 degree. The engine must be allowed to cool completely. Depending on conditions this will take a minimum of 6 hours.

1. Allow the engine and vehicle temperature to stabilize to that of the ambient (outside) air temperature.

Allowing the vehicle to stabilize overnight will ensure the most accurate results.

2. Turn the ignition ON but DO NOT start the engine.

Using a scan tool compare the ECT and IAT sensors. If both sensors do not indicate exactly the same temperature one of the sensors is inaccurate.

Do both sensors indicate the same temperature?

--

Go to Diagnostic Aids

Go to Step 4

4 |

Important: The IAT sensor must indicate the actual ambient temperature to within 1 degree. If the IAT sensor is accurate the ECT sensor must be inaccurate.

1. Place an accurate thermometer near the location of the IAT sensor.
2. Allow the thermometer temperature to stabilize.
3. Compare the thermometer reading to the IAT sensor temperature displayed on the scan tool. Refer to Diagnostic Aids.

Is the IAT sensor responding correctly to actual ambient temperature?

--

Go to Step 5

Go to Step 6

5 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
6 | Replace the IAT sensor. Refer to Intake Air Temperature Sensor Replacement . Did you complete the replacement? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --