For 1990-2009 cars

### Description

The powertrain control module houses the barometric pressure sensor and the circuitry. The powertrain control module uses barometric pressure information in order to adjust to the changes in altitude. The scan tool displays the barometric pressure sensor reading when the ignition switch is ON and the engine is OFF.

### Condition for Running the DTC

• | The engine is running at a steady speed.

• | The engine is operating in a Closed Loop.

### Conditions for Setting the DTC

The PCM compares with the MAP sensor and checks the following data:

• | The difference between the barometric pressure and the manifold absolute pressure is 26 kPa or more.

• | The ignition is ON for 2 seconds, and the engine is cranking for 2 seconds.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time that the diagnostic fails. The Freeze Frame buffer stores this information.

• | The MIL turns OFF after three consecutive trips, during which the diagnostic runs and there are not any faults that are detected.

• | A History DTC clears after 40 consecutive warm-up cycles without a fault.

• | Use the Clear DTC Information function on the scan tool, or disconnect the PCM battery feed in order to clear the DTC.

### Diagnostic Aids

A malfunctioning MAP sensor or a skewed MAP sensor may cause a DTC P1451 to set.

Barometric pressure varies depending on the weather conditions and depending on the altitude.

If a DTC P1451 cannot be duplicated, the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was set.

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the applicable Freeze Frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.

2. This step checks for a MAP sensor fault.

3. This step determines if the fault is present.

4. This step checks that the MAP sensor is reading atmospheric pressure. Normal atmospheric pressure will be near 100 kPa at sea level. If the engine is not running, intake manifold pressure and atmospheric pressure should be the same.

Step | Action | Value(s) | 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 | Check for MAP sensor DTC P0106, for DTC P0107, or for DTC P0108. Is a MAP sensor DTC set? | -- | Go to the applicable DTC table | Go to Step 3
3 |

1. Turn ON the ignition, leaving the engine OFF.
2. Clear the scan tool information.
3. Operate the vehicle within the specified Freeze Frame conditions.

Is DTC P1451 set?

--

Go to Step 4

Go to Diagnostic Aids

4 |

1. Turn ON the ignition, leaving the engine OFF.
2. Select the MAP sensor parameter on the scan tool.

Is the barometric pressure indicated by the MAP sensor near the specified value?

100 kPa (14.5 psi)

Go to Step 5

Go to Diagnostic Aids

5 | Replace the PCM. Is the action complete? | -- | Go to Step 6 | --
6 |

1. Perform the Clear DTC Information function on the scan tool, and road-test the vehicle within the Freeze Frame conditions which set the DTC.
2. Review the scan tool data, and check the data for DTCs. The repair is complete if no DTCs are displayed.

Does the scan tool display any DTCs?

--

Go to the applicable DTC table

System OK