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

The ignition is ON or the engine is running.

The PCM performs a comparison with the MAP sensor checking for the following conditions:

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

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 a DTC P1451 appears in the Not Ran Since Code Cleared list, the P1451 diagnostic has not yet run. When the 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. 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 vehicle operating conditions when the DTC was first set.

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.