For 1990-2009 cars

### Description

The barometric pressure (BARO) sensor and circuitry are located inside of the powertrain control module (PCM). The PCM uses the barometric pressure information in order to compensate for altitude changes. The BARO sensor reading is displayed on a scan tool when the ignition switch is On and the engine is off.

### Condition for Running the DTC

The engine is running in Closed Loop.

### Conditions for Setting the DTC

• | The engine is operating in the Fuel Cut-off mode.

• | The difference between the observed barometric pressure reading and the manifold absolute pressure (MAP) sensor reading is not within a specified value.

• | The above conditions are met for 5 seconds or more.

### Action Taken When the DTC Sets

• | The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.

• | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

### Conditions for Clearing the MIL/DTC

• | The MIL turns off after 3 consecutively passing trips without a fault present.

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

• | Perform the scan tool Clear DTC Information function.

### Diagnostic Aids

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

The barometric pressure varies depending on the weather conditions and the altitude.

If the DTC P1451 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P1451 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If DTC P1451 appears in the Not Ran Since Code Cleared list, the P1451 diagnostic has not yet run. When DTC P1451 does not appear in the Not Ran Since Code Cleared list, the P1451 diagnostic has run. If the MIL is NOT illuminated, and there is no Pending DTC Status in DTC Information, the P1451 diagnostic has passed. The DTCs MUST be cleared in order to view the Current Status of the Not Ran Since Code Cleared list. DO NOT forget that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for Current or Pending status in order to determine the outcome of the diagnostic test involved.

If a DTC P1451 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC was first 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 store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool 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. When 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 DTC P1408. Is DTC P1408 set? | -- | Go to DTC P1408 Manifold Absolute Pressure (MAP) Sensor Circuit | 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 Freeze Frame conditions as specified.

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 MAP sensor display or the barometric pressure reading at approximately the specified value?

100 kPa

Go to Step 5

Go to Diagnostic Aids

5 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | Go to Step 6 | --
6 |

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

Are any DTCs displayed on the scan tool?

--

Go to Diagnostic Trouble Code (DTC) List

System OK